Journal of Genetic Counseling, Vol. 6, No, 4, 1997

Update and Review: Maternal Serum Screening Kelly E. Ormond1'2

Maternal serum levels of alpha fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) can be used to screen pregnancies for neural tube defects, Down syndrome, Trisomy 18, and pregnancy complications. This article summarizes the most recent information regarding maternal serum screening, including genetic counseling issues. KEY WOKDS: maternal serum screening; alpna-tetoprotein.

INTRODUCTION

A screening program provides a low risk way to obtain information which might be useful to participants. Screening programs should enable treatment of the identified condition, or decision-making regarding further testing or actions based on screening information. Criteria for screening should include: a disease that is relatively frequent within the populations to be screened, a disease that is severely impairing or fatal, and some beneficial intervention must be feasible based on screening outcomes. A screening test should be highly sensitive and specific, and have a relatively high predictive value (as defined below). Screening programs should involve prompt testing and follow-up, include an educational component, and be voluntary. Finally, in order for a screening test to be effective, the benefits should outweigh the costs, both financial and psychological. 'University of Vermont College of Medicine, Department of Pediatrics, Burlington, Vermont. Correspondenceshould be directed to Kelly Ormond, Northwestern Memorial Hospital, 333 E. Superior (Suite 1565), Chicago, Illinois 60611.

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Screening can lead to four possible outcomes: (1) true positive result—screening correctly identifies person as affected with condition, (2) false positive—screening incorrectly identifies an unaffected person as affected, (3) true negative—screening correctly identifies person as unaffected, and (4) false negative—screening incorrectly identifies an affected person as unaffected. Good screening measures maximize the number of true positive and negative results, while minimizing the false positive and negative results. Sensitivity is defined as the proportion of individuals affected by a condition who have a positive test result (true positives/all those with the disease). Sensitivity indicates how accurate a measure is in identifying those with a certain condition. False negative results occur when an affected individual receives a negative result and is therefore not detected by screening; good screening measures have low false negative rates. For example, if a screening measure is 95% sensitive, it correctly identifies 95/100 cases, and the false negative rate is 5/100 (5%). Specificity is defined as the proportion of those unaffected persons who have a negative test (true negatives/all those without disease). Specificity indicates how accurate a screen is in identifying those without a specific condition. False positive results occur when an unaffected person receives a positive screening result; diagnostic testing is often required to separate true positives from false positives. If a screening measure is 95% specific, this means that 95% of unaffected persons will receive a negative result, and that 5% of unaffected persons will have an initial positive (or false positive) result. Positive predictive value is the proportion of persons with a positive screening test who actually are affected with the condition screened for (true positives/all positives). Positive predictive value considers the prevalence of a condition in the population screened. As the prevalence of the condition decreases, the false positive rate increases and positive predictive value decreases; as the prevalence of a condition increases, so does the positive predictive value of a positive screen. For example, as a woman's age increases, so does the positive predictive value of an increased risk for Down syndrome on maternal serum screening. Sensitivity and specificity are inversely related, and as one increases, the other decreases. Screening tests must find a balance between a high rate of sensitivity and specificity. Most screening produces a significant number of false positives in order to maximize detection while minimizing false negatives.

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MSAFP AND THE DETECTION OF NTDS In the United States, neural tube defects (NTDs) occur in about 12/1000 births and can be detected prenatally. However, 90-95% of all NTDs occur in families without a positive history, so most pregnant women are not offered diagnostic testing. Therefore, screening is most effective when offered to all pregnant women, particularly those in the low risk groups who would not otherwise be offered testing, rather than merely targeting women with a positive family history of an NTD. Elevated levels of alpha-fetoprotein (AFP) in amniotic fluid samples are associated with the presence of neural tube defects (NTDs), including spina bifida and anencephaly (Brock and Sutcliffe, 1972). AFP is known to cross the placenta (Brock et ai, 1973) and since the 1970s, maternal serum alpha-fetoprotein (MSAFP) has been used to screen for NTDs during pregnancy (Wald and Cuckle, 1977). In 1985, the American College of Obstetricians and Gynecologists (ACOG) recommended that all pregnant women should be offered MSAFP screening for NTDs (ACOG, 1985). Since that time, MSAFP screening for NTDs in low risk women has become common obstetrical practice. MSAFP is detectable in the first trimester and increases until 3032 weeks gestation. AFP values are converted from raw data into "Multiples of the Median" or "MOMs." Maternal weight, insulin-dependent diabetes, the presence of multiple gestations and maternal race also affect the calculation of MSAFP medians. Although AFP is detectable earlier, median values are typically reported from 14-21 weeks gestation. The best time for detecting NTDs by measuring MSAFP appears to be 16-18 weeks gestation (Wald and Cuckle, 1977). A small proportion of laboratories perform screening analysis even after 22 weeks gestation, although the reliability of screening at this later date is not well documented (Palomaki et al, 1993). In a pregnancy affected with an NTD, MSAFP levels are typically elevated. However, the MSAFP values in unaffected pregnancies significantly overlap with levels in pregnancies affected with an NTD (Fig. 1). Maternal weight has an effect on the calculation of MSAFP because increased plasma volume in larger women can dilute the amount of AFP present and, if not corrected for, might lead to a mistakenly low calculation of the AFP value. Conversely, AFP concentrations may be falsely elevated in smaller women. Disregarding a woman's weight could potentially lead to misclassifying a pregnancy as high or low risk for an NTD (Adams et al., 1984).

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Fig. 1. Distribution of MSAFP levels in Down syndrome, unaffected and open spina bifida pregnancies. Reproduced with permission from Wald and Cuckle (1988).

Women who have insulin-dependent diabetes (IDDM) have, on average, lower AFP levels, but also have an elevated risk for NTD during pregnancy (Milunsky et al, 1982). Without statistical correction for diabetic status, a number of NTDs might be missed in this high risk group. AFP levels and risk for NTDs are not affected by gestational diabetes, and no correction is necessary for these women. Multiple gestation is associated with increased levels of AFP and other analytes. A section on twin pregnancy and maternal serum screening is presented later in this article. African-American women have a tendency toward a higher level of AFP (10-15% higher than Caucasian women), but have a lower prevalence of NTDs. MSAFP is also slightly increased in women of Asian background, and slightly decreased in Hispanic women (Crandall et al, 1983; Benn et al, 1997). By correcting for maternal race, a more accurate risk assessment can be given. Elevated MSAFP levels suggest an increased risk for NTDs such as open spina bifida or anencephaly, and follow-up is recommended (see below). To maximize detection of affected pregnancies and minimize false positive results, MSAFP cutoffs are established at 2.0 or 2.5 MOM, depending on the screening center. At a cutoff of 2.0 MOM, approximately 5% of those screened will have an initial positive result; at 2.5 MOM, 4% will screen positive. At these cutoffs, sensitivity is approximately 80-90% for open spina bifida and greater than 90% for anencephaly (Wald and

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Cuckle, 1977; Milunsky et al, 1989). It is difficult to detect closed spina bifida since MSAFP levels are often not elevated. In addition, 75-90% of open ventral wall defects (e.g., omphalocele or gastroschisis) are detected, depending on the MSAFP cutoffs used by a screening center (Palomaki et al., 1988). Sensitivity is greater for gastroschisis than for omphalocele, regardless of cutoff chosen (Palomaki et al, 1988). Other reasons for elevated MSAFP include but are not limited to: the underestimation of gestational dates, multiple gestation pregnancy, fetal demise, congenital nephrosis, polycystic kidneys, renal obstructions, esophageal atresia, duodenal obstruction, teratoma, cystic hygroma, hydrops, fetal skin disorders, oligohydramnios, placental anomalies, maternal tumor, and fetal chromosome abnormalities (Burton, 1988; Thomas and Blakemore, 1990).

Management of Women with an Elevated MSAFP Screen

The protocol for managing an elevated MSAFP varies. Generally, an ultrasound is performed to assure correct gestational dating and the presence of a viable singleton pregnancy. Approximately 40% of the time, gestational dating is incorrect (usually underestimated), and the MSAFP value is recalculated if discrepant by more than 1-2 weeks (Canick and Knight, 1992). As routine dating ultrasounds become more common in practice, the false positive rate is expected to decrease (Wald et al., 1992). Because spina bifida decreases the biparietal diameter (BPD) of a fetus, dating by this measurement significantly increases the detection of spina bifida by yielding an apparently earlier gestational age and making the MSAFP value appear even higher (Wald et al., 1980). When a multiple gestation pregnancy is present, the MSAFP reading is interpreted to reflect this (see section on twin pregnancy). For women with a normal recalculation based on ultrasound dating, no further testing is recommended. When gestational dates are confirmed by ultrasound, MSAFP can be repeated in women with an initial MSAFP of 2.0-2.99 MOM. MSAFP levels tend to regress toward the mean of their group as gestational age increases (Knight et al., 1988). For pregnancies affected with an NTD, this regression would result an increase in MSAFP level from the first draw, while for unaffected pregnancies it usually results in a decrease in MSAFP level. Thirty to forty percent of women with an initially elevated MSAFP will have a normal level on repeat sample; this significantly lowers their risk of NTD (Burton, 1988). No further testing is indicated in this group of women.

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Women who have an initial level of MSAFP greater than 3.0 MOM or a repeat MSAFP level greater than 2.0 MOM are offered a high resolution (level II) ultrasound examination by an experienced sonographer to screen for anencephaly, spina bifida, and other fetal defects. Currently, there is controversy over whether amniocentesis is indicated after an elevated MSAFP and normal level II ultrasound. On one hand, the diagnosis of NTDs is highly accurate via amniocentesis (99% detection), as it measures both amniotic fluid AFP levels (AFAFP) and acetylcholinesterase (AChE). In addition, about 1% of pregnancies with an "unexplained" elevated MSAFP have aneuploidy, particularly those women with MSAFP greater than 2.5 MOM (Feuchtbaum et al, 1995). There is also an increased risk of aneuploidy when an NTD or abdominal wall defect is present (Harmon et al, 1995). On the other hand, when optimal views of the fetal spine and skull are obtained by an experienced sonographer via high resolution ultrasound, some perinatologists feel this decreases the risk of NTD by at least 95% (Nadel et al, 1990). Based on this low remaining risk, some feel that amniocentesis is not warranted when level II ultrasound appears normal (Nadel et al, 1990; Stiller et al, 1990; Benacerraf, 1993; Sepulveda et al, 1995; Thiagarajah et al, 1995). Amniocentesis may be more strongly considered when ultrasound does not allow optimal visualization, or if the MSAFP is significantly elevated (e.g., 35 MOM or greater) (Benacerraf, 1993). Other centers will perform amniocentesis for AFAFP analysis, but will not perform fetal karyotyping because of the lower risk of fetal aneuploidy (Stiller et al, 1990). Each center must decide what is appropriate and apprise women of their options and the related risks and benefits of each option. When spina bifida or anencephaly is detected and the pregnancy is continued, the patient is often followed by perinatologists. Cases of anencephaly are uniformly fatal, most often within the first days or weeks of life. For spina bifida, the prognosis is more variable. Some researchers recommend the fetus with spina bifida be delivered by cesarean section prior to the onset of labor (Luthy et al, 1991), although it is controversial to what degree this might lessen neurological damage. In many cases, surgery can be performed within 24 hours after birth to close the spinal column, and a shunt can be placed if necessary. Most infants with spina bifida will have some degree of paralysis below the anatomical level of the lesion, including difficulties with walking and bowel/bladder control. Some infants with spina bifida have developmental delays secondary to hydrocephalus (Cochrane et al, 1996). It is important to remember that NTDs can be associated with aneuploidy or other syndromes, and determining the etiology of an NTD is necessary to providing correct recurrence risk counseling. Psychological support of families who choose to continue a pregnancy after an abnormality is detected can help facilitate parental adjustment.3 3 An

excellent resource for families continuing a pregnancy with spina bifida is "Now that you've been told your baby has spina bifida" (NSGC, 1993).

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Recurrence Risks The recurrence risk for an NTD is related to the general population frequency; in the United States, the frequency is 1-2/1000 births. In places such as the United Kingdom, which have a higher general population incidence, the recurrence risks will be increased above those presented below (Wald and Cuckle, 1977). When there is a history of a prior pregnancy with an isolated NTD, or if either parent has an NTD, the recurrence risk is 2-4%. With two affected first degree relatives (usually two children), this risk increases to 5-10%. For second-degree relatives, the recurrence risk is approximately 1%, and for third-degree relatives, the risk is approximately the same as the general population risk (Toriello and Higgins, 1983). When an NTD is associated with other anomalies, it is important to consider other syndromes in the differential diagnosis, as a syndromic etiology may significantly change the recurrence risk. Folic Acid Supplementation Recent studies have suggested that folic acid taken preconceptionally and in the first trimester of pregnancy can decrease both the occurrence and recurrence of NTDs, perhaps by up to 50-70% (CDC, 1992). All women, regardless of a prior history of NTD, should consume the recommended daily allowance (RDA) of 0.4 mg folic acid per day both preconceptionally and throughout the first trimester of pregnancy; this is the amount of folic acid found in most multivitamins. Women with a family history of NTD should consume the RDA of 0.4 mg/day of folic acid on a regular basis, even when not contemplating pregnancy. Several months prior to planning a pregnancy they should speak with their health care practitioner about starting 4.0 mg/day of folic acid preconceptionally and continuing this dosage throughout the first trimester (CDC, 1992; Baty et al, 1996). SCREENING FOR ANEUPLOIDY WITH MATERNAL SERUM SCREENING Screening for Down Syndrome in Women Under 35 Years of Age Most babies with Down syndrome are born to women under 35 years old; while women over 35 are becoming pregnant more frequently, only 5-10% of pregnant women are 35 years of age or older. Therefore, offering diagnostic testing based on maternal age alone will detect approximately 20-30% of fetuses with Down syndrome (Haddow et al, 1992). Women under 35 years of

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age are considered at lower risk for aneuploidy and are not routinely offered diagnostic testing. Maternal serum screening can identify younger women whose risk for Down syndrome is equal to or greater than the risk of a 35-year-old woman. Such women can then be offered diagnostic testing. When introduced in the 1980s, serum screening for Down syndrome examined levels of MSAFP alone. Decreased levels of MSAFP (0.7 MOM or less) have been associated with increased risks for Down syndrome (Merkatz et al, 1984; Cuckle et al, 1984). However, there is considerable overlap between MSAFP levels of an unaffected fetus and a fetus with Down syndrome (Fig. 1). Screening combines the MSAFP level with the woman's age to achieve a risk calculation (Knight et al, 1988). A cutoff is chosen to differentiate women not at increased risk versus women at high risk on the basis of the serum screening. As with screening for NTDs, the cutoffs are chosen to maximize sensitivity and minimize the false positive rate. While each laboratory may use a different cutoff, it is usually equivalent to a mid-trimester risk of 1/270 for Down syndrome, the same risk as a 35-year-old woman. Other laboratories choose a cutoff of approximately 1/190 in order to maintain an initial positive rate of 5%. With MSAFP alone, screening detects approximately 25% of Down syndrome in women under 35 years of age, with an initial positive rate of about 5% (NERGG, 1989). Additional markers are available which increase the sensitivity of maternal serum screening for Down syndrome without increasing the false positive rate. Screening programs utilize various combinations of markers, most commonly MSAFP, human chorionic gonadotropin (hCG) (Bogart et al, 1987) and unconjugated estriol (uE3) (Canick et al, 1988). "Double Screening" typically utilizes combinations of MSAFP and hCG with age, as hCG seems to be a better predictive marker than uE3 in Down syndrome screening. The sensitivity of double screening which utilizes AFP and hCG is approximately 55%, and has an initial positive rate of approximately 5% (Mooney et al, 1994). Using "Triple Marker Screening" (MSAFP, uE3, and total hCG) and a cutoff equivalent to a 1/270 mid-trimester risk, the sensitivity for Down syndrome is approximately 60-65% in women under 35 years of age with false positives averaging 5-6% (Haddow et al, 1992; Wald et al, 1988). Some laboratories offer "Four-Marker Screening," including MSAFP, uE3, and both free (B-hCG and free oc-hCG. Wald et al suggests a detection rate of 72% with a similar initial positive rate to triple marker screening (Wald et al, 1994). Of course, regardless of which screening method is used, the rate of detection and initial positive rate vary with the age of women screened (Reynolds et al, 1993; Bishop et al, 1996) and the specific cutoffs used by each screening program. Currently, ACOG (1994) recommends offering serum screening to all pregnant women, but does not suggest any specific combination of markers for this screening. The American College of Medical Genetics (ACMG) also recommends that some form of multiple marker screening should be offered to all pregnant women (ACMG, 1996).

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Screening for Trisomy 18 When all three markers (AFP, uE3, hCG) are low, a pregnancy is considered at increased risk for Trisomy 18. Because of the small amount of data regarding specific risks, many screening programs provide a 1/15 risk of Trisomy 18 for any pregnancy considered at high risk based on certain cutoffs (AFP < 0.75 MOM; hCG < 0.55 MOM; uE3 < 0.60 MOM) (Canick et al, 1990a). An algorithm also exists to calculate age-specific risks for Trisomy 18 (Palomaki et al, 1995). Screening is 60-70% sensitive for Trisomy 18 with a false positive rate of approximately 0.5% (Canick et al, 1990a; Palomaki et al, 1992, 1995; Barkai et al, 1993). The presence of a neural tube defect or abdominal wall defect can alter these detection rates by elevating MSAFP levels. Detection of Triploidy with Maternal Serum Screening Triploidy is present in approximately 1% of conceptions, but significantly fewer second trimester fetuses. Triploid fetuses have been detected using the Trisomy 18 screening cutoffs, but the sensitivity of detection is unknown (Fejgin et al, 1992). Both decreased hCG (Fej'gin et al, 1992) and elevated hCG have been associated with triploidy (Oyer and Canick, 1992; Jauniaux et al, 1997). Triploidy has also been associated with elevated MSAFP (Burton, 1988). Jauniaux et al proposed a screening method combining first trimester ultrasound (such as crown-rump length, nuchal translucency, and fetal or placental anomalies) and hCG measurements between 10-14 weeks gestation to detect triploidy (Jauniaux et al, 1997). Maternal serum screening does not currently provide specific risk estimates for triploidy, as the sensitivity and specificity of such screening is unknown. Management of Women With Increased Risk for Down Syndrome or Trisomy 18 For women at increased risk for aneuploidy based on maternal serum screening, the first step in follow-up is to verify gestational age by ultrasound if this has not yet been performed. Approximately 50% of women who have an increased risk for Down syndrome have overestimated gestational dating (Haddow et al, 1992). If dating is inaccurate by more than a week to 10 days, the screening results can be recalculated (Canick and Sailer, 1993). Use of BPD is also important in dating pregnancies affected with Down syndrome, as femur length can underestimate gestational age (Cuckle and Wald, 1987). If the recalculated results are normal, no further testing is recommended. For women at increased risk for Trisomy 18, dating is not recalculated because of the association between Trisomy 18 and intrauterine growth retardation.

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Table I. Ultrasound Findings Associated with Down Syndrome Congenital heart defect Pyelectasis < 4mm (15-20 weeks) Duodenal atresia (double bubble) Hyperechoic small bowel Cystic hygroma

Nuchal thickness < 6mm (14-21 weeks) Shortened femur/humerus Hypoplasia of middle phalanx Increased iliac length Intrauterine growth restriction

Typically, when the risk is increased for aneuploidy, repeat samples are not obtained. This is because of the tendency of AFP and other analytes to regress toward the mean of the population they belong to. Since the mean levels of analytes for both the unaffected and Down syndrome populations may be higher than the screening cutoffs, redrawn samples from both populations are likely to regress to the mean. Therefore, re-drawing a sample is not particularly useful in separating truly affected pregnancies from false positives (Knight et al, 1988). After dating is verified, most centers offer genetic counseling and amniocentesis for fetal karyotype. Chromosome abnormalities aside from Down syndrome can be present, and genetic counseling should include information regarding other chromosomal abnormalities, including other autosomal aneuploidies and sex chromosome aneuploidy (Benn et al, 1995). There has been some suggestion that ultrasound screening for Down syndrome can be useful (Lockwood et al., 1987; Benacerraf et al., 1992), but this remains controversial. Experienced sonographers can detect signs of Down syndrome such as those listed in Table I (Hill, 1996). However, in the absence of any abnormal findings, the risk for Down syndrome is not eliminated, as a high percentage of fetuses with Down syndrome (perhaps as high as 60-65%) will not have major anomalies detectable on ultrasound (Nyberg et al., 1990; Benacerraf et al, 1992). Nyberg et al (1990) suggest that the sonographic detection of Down syndrome increases from 25% in the second trimester to approximately 80% in the third trimester. For pregnancies at increased risk for Trisomy 18, ultrasound screening can be also useful (Benacerraf et al, 1988; Bundy et al, 1986). An experienced sonographer can detect signs associated with Trisomy 18 as listed in Table II (Hill, 1996). While most fetuses with Trisomy 18 have some structural anomaly (Benacerraf et al, 1988), a recent study suggests that 10-20% do not have structural malformations detectable on ultrasound at 14-24 weeks gestational age (Nyberg et al, 1993). Therefore, a normal level II ultrasound cannot absolutely rule out Trisomy 18, and patients should be offered amniocentesis. However, some patients with normal high resolution ultrasound may wish to forego testing based on the low remaining risks.

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Table II. Ultrasound Findings Associated with Trisomy 18 Poor growth for gestational age Clenched fists with overriding digits Cardiac defects (esp. polyvalvar) Choroid plexus cysts Cleft lip Other structural abnormalities

Limb reduction anomalies Rockerbottom/club feet Hernias Renal anomalies Polyhydramnios

A sample protocol for both NTD and aneuploidy screening is outlined in Fig. 2. As one can see from the complexity of this protocol, it is important to perform maternal serum screening in a context which allows for the appropriate follow-up of abnormal screening results.

Fig. 2. Management of abnormal maternal serum screening results.

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Management of Aneuploid Pregnancies and Recurrence Risks

When a pregnancy is identified with a chromosome abnormality, the couple should be counseled regarding the prognosis and provided with a complete range of options and psychosocial support in their decision-making. Often, level II ultrasound or fetal echocardiograms will be performed to detect associated anomalies such as cardiac defects. In addition, 30-35% of fetuses with Down syndrome and 60-70% of fetuses with Trisomy 18 detected at mid-trimester are miscarried or stillborn (Hook et al., 1995). When a pregnancy with Down syndrome is continued, unless the infant has identified medical problems, the delivery management is usually not altered. For infants with aneuploidy and additional medical problems, a perinatologist may be involved in managing the pregnancy. When a trisomic pregnancy occurs, the recurrence risk is approximately 1% or a woman's age-related risks, whichever is greater, for having a child with a chromosome abnormality (Cooley and Graham, 1991). When a translocation is detected, parental karyotyping should be performed to provide accurate recurrence risks. It is appropriate to offer prenatal diagnosis in future pregnancies to women who have had a pregnancy with a trisomy. SERUM SCREENING IN WOMEN OVER 35 Serum screening in women over 35 years of age is controversial. Some suggest it is useful because it decreases the number of amniocenteses performed in women of this age group (Haddow et al, 1994). However, at this point, maternal serum screening is not considered a replacement for diagnostic amniocentesis to women older than 35 (ACOG, 1994; ACMG, 1996), particularly because screening does not specifically detect nor rule out other chromosome abnormalities for which these women are also at increased risk. Women 35 and older are more likely to have an initial positive result on serum screening (at least 25%), simply because their age-related risks are higher than the cutoff (Haddow et al, 1994). However, the detection of Down syndrome when screening women over 35 years of age might be as high as 80-90% (Haddow et al, 1994). Each center must consider these issues and women of this age group must be counseled to allow informed decisions about diagnostic testing versus serum screening.

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SCREENING FOR PREGNANCY COMPLICATIONS Much more controversial is the interpretation of maternal serum screening for pregnancy complications. Women with an increased MSAPP but normal fetuses are at increased risk for complications such as pregnancy loss, pre-term birth, low birthweight (LBW), and preeclampsia (Brazerol et al, 1994; Crandall et al., 1991; Maher et al., 1994). While AFAFP levels are also predictive of adverse outcomes (Crandall and Matsumoto, 1991), MSAFP is thought to be a better predictor (Wenstrom et al., 1996). Serial MSAFP measurements are not more helpful than a single measurement in predicting an increased risk for pregnancy complications (Wenstrom et al, 1992). Increased hCG levels also suggest an elevated risk for fetal/neonatal death, pre-term birth, LBW, and pre-eclampsia (Beekhuis et al, 1992; Walters and McKinnon, 1993; Wenstrom et al, 1994; Benn et al., 1996). Pergament and colleagues (1995) noted that women with a false positive screen for Down syndrome (risk of 1/250 or greater) had a significantly increased risk for adverse outcomes. The combination of increased MSAFP and increased hCG are associated with a particularly increased risk of adverse pregnancy outcome. There is little agreement among obstetricians regarding the usefulness of this information, and how best to counsel and manage patients who fall into these increased risk groups. However, ACMG (1996) does not recommend serum screening for the sole purpose of screening for pregnancy complications, particularly since the efficacy of various antepartum interventions is not yet established.

SERUM SCREENING AND OTHER ASSOCIATED ANOMALIES Significantly low levels of uE3 have been associated with an increased risk for pregnancy loss (Santolaya-Forgas et al, 1996), X-linked ichthyosis (steroid sulfatase deficiency) (Bartels et al, 1994; David et al, 1995; Keren et al, 1995; Zalel et al, 1996), Smith-Lemli-Opitz syndrome (Blitzer et al, 1994; Rossiter et al, 1995), and congenital adrenal hypoplasia (Peter et al, 1996). There have also been associations with lipoid congenital adrenal hyperplasia (Izumi et al, 1993; Saenger et al, 1995) and triploidy (Fejgin et al, 1992).

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FUTURE DIRECTIONS IN MATERNAL SERUM SCREENING Other markers have been investigated for use in second trimester maternal serum screening for Down syndrome. Among others, these include inhibin, total hCG, free a-hCG, free p-hCG, CA-125, and pregnancy associated plasma protein A (PAPP-A). In addition, the sensitivity of first trimester serum screening for Down syndrome is currently being widely investigated. As was seen for markers in the second trimester, there is significant overlap for each marker investigated between affected and unaffected pregnancies. Currently, it appears that PAPPA and free p-hCG will be the most useful markers in first trimester screening. Screening can be performed as early as 10 weeks gestational age, and screening with age, PAPP-A, and free (B-hCG will allow approximately 62-79% detection for Down syndrome, while maintaining an initial positive rate of 5% (Brambati et al, 1994; Wald et al, 1995,1996). Casals et al. (1996) also found a sensitivity of 82% for PAPP-A and AFP screening during the first trimester. Currently, first trimester serum screening remains under investigation. While first trimester screening for Down syndrome provides the obvious benefit of earlier information for follow-up diagnostic studies and decision-making, several concerns exist regarding first trimester screening. These include the increased frequency of miscarriage in an affected pregnancy detected at 10 weeks gestation, the increased procedural risks associated with CVS or early amniocentesis, and difficulty in screening for neural tube defects in the first trimester.

TWIN PREGNANCIES AND SERUM SCREENING In an unaffected twin pregnancy, the levels of MSAFP, hCG, and uE3 are about twice that of a singleton pregnancy (Alpert et al,, 1990; Canick etal., 1990b; Wald et al, 1991). Some pregnancies with an elevated MSAFP level are due to the presence of multiple fetuses. In known twin gestations, these levels can be roughly divided by two to obtain an approximate MOM comparable to a singleton pregnancy (Wald et al, 1991; Neveux et al, 1996); most laboratories simply use a cutoff of approximately 5.0 MOM in order to maintain similar initial positive rates in known twin gestations. In screening for NTDs, using a 5.0 MOM cutoff can detect approximately 83% of anencephaly and 39% for open spina bifida. In screening for Down syndrome, the above method should result in a false positive rate similar to that seen in singleton pregnancies, but the detection rate in multiple gestations is unknown and most likely less reliable (Wald et al, 1991; Neveux et al, 1996).

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COUNSELING ISSUES RELATED TO MATERNAL SERUM SCREENING

Genetic counseling includes both educational and psychological components which ideally facilitate autonomous decision making in our patients (LeRoy, 1993). Both counselors and patients see the primary components of genetic counseling as providing information, risk assessment, helping patients achieve understanding, facilitating decision-making, and providing support (Allanson et al, 1996). In many ways, genetic counseling impacts perception of genetic risks. The mere existence of maternal serum screening programs challenges risk perception in several ways. First, the availability of screening in women at low risk raises awareness that any woman can have a fetus with Down syndrome (Green and Statham, 1996). Simply raising the topic of risk can influence one's risk perception. Many women undergo screening for reassurance, rather than to detect an abnormality (Farrant, 1980). This, combined with the "routineness" of serum screening may explain why a high number of women undergo screening (Green and Statham, 1996). Unfortunately, when the expected reassurance is replaced with an increased risk result, anxiety can be significant. Patient anxiety is a criticism of widespread screening programs, including maternal serum screening. Clearly, positive maternal serum screening results during pregnancy can increase maternal anxiety (Farrant, 1980; Fearn et al, 1982; Robinson et al, 1984; Burton et al, 1985; Evans et al, 1988; Marteau et al, 1992a, 1989; Abuelo et al, 1991; Keenan et al, 1991). In addition, the anxiety of patients who have a positive AFP screen is greater than the anxiety of advanced maternal age patients with similar risks (Evans et al, 1988; Abuelo et al, 1991), This suggests that the labeling of "at risk" is more important than the actual risk assessment in developing the patient's perception of risk (Marteau et al, 1991; Lowry et al, 1995). "To have doubt cast upon the health of the fetus is very stressful especially for a woman with no a priori reason to consider herself at risk" (Green, 1990). Perhaps abnormal screening results acutely increase the awareness of the risk of fetal abnormalities (Marteau et al, 1991). Prenatal testing or screening forces women to face the risk of an abnormal result (Kolker and Burke, 1987). Perhaps for screening patients, the risk is perceived as greater, leading to an increased anxiety level. One aspect crucial to maternal serum screening programs is pretest education and informed consent. Patients must have the necessary background to make a decision about serum screening (Standing Medical Advisory Committee, 1979). ACOG (1992) also stresses the importance of education in maternal serum screening programs. Despite this, genetic counselors anecdotally report that patients with a positive serum screen

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result frequently misunderstand the meaning of screening results. Most patients are not familiar with the concept of screening versus a diagnostic test result; this may not be for lack of education about screening. Some patients may not receive specific information regarding screening, while others might not understand it or may not recall it for various reasons (Marteau et al, 1988; Michie and Marteau, 1996). Unfortunately, misconceptions about screening lead to increased anxiety and dissatisfaction with the screening process. In fact, in one study of women with a positive serum screen, 65% reported feeling anxious and 21% would not have serum screening performed in a future pregnancy (Early et al., 1991). Studies have only recently begun to investigate which methods are most effective in educating patients regarding maternal serum screening (Thornton et al., 1995; Ormond et al, 1996), but data suggests that a combination of discussion and written information (e.g., pamphlets) prior to screening is most helpful in increasing knowledge and decreasing anxiety. Marteau et al. (1993) suggests that written information regarding serum screening leads to increased knowledge and satisfaction with the amount of information provided, despite the fact that anxiety was not altered significantly. Genetic counseling has been associated with a decrease in anxiety, both in advanced maternal age patients (Ruiz-Bueno et al., 1991) and patients with an increased risk based on serum screening (Keenan et al., 1991). The genetic counselor's role following a positive maternal serum screen is to help the patient understand the screening program and the meaning of the results, to facilitate decision-making and to act as a source of psychological support to the patient. The provision of psychological support is particularly important in patients at increased risk based on serum screening because of the increased anxiety noted. For women with a positive serum screen result, a normal ultrasound is also associated with a short-term decrease in anxiety (Tsoi et al., 1987). After receiving normal amniocentesis results, anxiety levels usually return to their prescreening levels for the remainder of the pregnancy (Robinson et al, 1984; Marteau et al, 1992b). While screening tests cause anxiety in some women, they appear to offer reassurance to others (Kidd et al, 1993). Normal maternal serum screening results do not seem to increase anxiety in pregnancy (Burton et al, 1985; Kidd et al, 1993). For many women, in fact, screening helps alleviate anxiety about the pregnancy. One might wonder if this may, in part, be due to a tendency to misunderstand the possibility of false negatives. Many women tend to globalize normal serum screening results to mean the baby is healthy and unaffected with conditions other than those screened for (Faden et al, 1985). Women who are not informed of normal

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results experience increased anxiety, suggesting that women should be told of normal serum screening results, rather than taking a "no news is good news" approach (Fearn et al, 1982). Interestingly, some women who decline maternal serum screening have elevated anxiety later in pregnancy compared to women who underwent screening (Burton et al, 1985; Marteau et al., 1989; Berne-Fromell and Kjessler, 1984) supporting the notion that screening can alleviate some anxiety in pregnancy. Some controversies still remain regarding the benefits of maternal serum screening during pregnancy. These include the question of cost-effectiveness, the effect of screening on the disability community (Elkins and Brown, 1993), and the effect of anxiety on a large number of women receiving false positive results in relation to number of affected fetuses detected through screening (Green, 1990). It remains that a high proportion of women are interested in undergoing serum screening during pregnancy (Tymstra et al, 1991). Health care professionals such as genetic counselors will continue to need to outline the complexities of maternal serum screening in order to encourage autonomous decision-making in patients. CONCLUSIONS

Maternal serum screening has become a widely used method for identifying low risk women who are at an increased risk for NTDs or Down syndrome and offering them the option of diagnostic testing. Additional markers may lead to an increased sensitivity and specificity in future years. Anxiety has been associated with false positive results, and methods such as genetic counseling and ultrasound appear to decrease this anxiety, at least in the short term. Pretest education is an important way to decrease any anxiety related to maternal serum screening during pregnancy. ACKNOWLEDGMENTS

Thanks to Janice Berliner, Carol Goodwin, Christine Miller, and Carol P. Walters for their helpful comments in the development of this manuscript. REFERENCES Abuelo DN, Hopmann MR, Barsel-Bowers B, Goldstein A (1991) Anxiety in women with low maternal serum alpha-fetoprotein screening results. Prenat Diagn 11:381-385. ACOG Dept. Professional Liability Alert—May 1985 (1985) Professional Liability Implications of AFP Tests.

412

Ormond

ACOG Technical Bulletin No 154—April 1991 (1992) Alpha-Fetoprotein. Int J Gynecol Obstet 38:241-247. ACOG Committee Opinion No 141—August 1994 (1994) Down Syndrome Screening. Adams MJ, Eindham GC, James LM, et al. (1984) Clinical interpretation of maternal serum oe-fetoprotein concentrations. Am J Obstet Gynecol 148:241. Allanson A, Michie S, Bobrow M, Marteau TM (1996) The objectives of genetic counseling: A comparison of patients' and professionals' views. J Med Genet 33:S36. Alpert A, Greenberg F, Conant C, Schmit D, Weyland B, Darnule A, Rose E (1990) Serum hCG, AFP and unconjugated estriol levels in twin pregnancies in mid-trimester. Am J Hum Genet 47:A267. American College of Medical Genetics (ACMG) (1996) ACMG Position Statement on Multiple Marker Screening in Women 35 and Older. Barkai G, Goldman B, Reis L, Chaki R, Zer T, Cuckle H (1993) Expanding multiple marker screening for Down syndrome to include Edwards syndrome. Prenat Diagn 13:843-850. Bartels I, Caeser J, Sancken U (1994) Prenatal detection of X-linked ichthyosis by maternal serum screening for Down syndrome. Prenat Diagn 14:227-229. Baty BJ, Cohen L, Phelps L, Speer MC, Stengel P, Williamson-Kruse L (1996) Folic Acid and the Prevention of Neural Tube Defects. A Position Paper of the National Society of Genetic Counselors. JGC 5:139-145. Beekhuis JR, Van Lith JMM, DeWolf BTHM, Mantingh A (1992) Increased maternal serum alpha-fetoprotein and human chorionic gbnadotropin in compromised pregnancies other than for neural tube defects or Down syndrome. Prenat Diagn 12:643-647. Benacerraf BR (1993) Should patients with elevated levels of maternal serum alphafetoprotein always undergo amniocentesis? Radiology 188:17. Benacerraf BR, Miller WA, Frigoletto FD (1988) Sonographic detection of fetuses with Trisomy 13 and 18: Accuracy and limitations. Am J Obstet Gynecol 158:404. Benacerraf BR, Neuberg D, Bromley B, Frigoletto FD (1992) Sonographic scoring index for prenatal detection of chromosome abnormalities. J Ultrasound Med 11:449-458. Benn PA, Home D, Briganti S, Greenstein RM (1995) Prenatal diagnosis of diverse chromosome abnormalities in a population of patients identified by triple-marker testing as screen positive for Down syndrome. Am J Obstet Gynecol 173:496-501. Benn PA, Home D, Briganti S, Rodis JF, Clive JM (1996) Elevated second-trimester maternal serum hCG alone or in combination with elevated alpha-fetoprotein. Obstet Gynecol 87:217-222. Benn PA, Clive JM, Collins R (1997) Medians for second trimester maternal a-fetoprotein, human chorionic gonadotropin, and unconjugated estriol; differences between races or ethnic groups. Clin Chem 43:333-337. Berne-Fromell K, Kjessler B (1984) Anxiety concerning fetal malformations in pregnant women exposed or not exposed to an antenatal serum alpha-fetoprotein screening program. Gynecol Obstet Invest 17:36-39. Bishop J, Dunstan F, Nix B (1996) Down's syndrome screening: Equal risks for all? Br J Obstet Gynaecol 103:391-392. Blitzer MG, Kelley RI, Schwartz MF (1994) Abnormal serum marker pattern associated with Smith-Lemli-Opitz (SLO) syndrome. Am J Hum Genet 55:A277. Bogart MH, Pandian MR, Jones OW (1987) Abnormal maternal serum chorionic gonadotropin levels in pregnancies with fetal chromosome abnormalities. Prenat Diagn 7:623-630. Brambati B, Tului L, Bonacchi I, Shirmanker K, Suzuki Y, Grudzinskas JG (1994) Serum PAPP-A and free p-hCG are first trimester screening markers for Down syndrome. Prenat Diagn 14:1043-1047. Brazerol WF, Grover S, Donnenfeld AE (1994) Unexplained elevated maternal serum a-fetoprotein levels and perinatal outcome in an urban clinic population. Am J Obstet Gynecol 171:1030-1035. Brock DJH, Sutcliffe RG (1972) Alpha fetoprotein in the antenatal diagnosis of anencephaly and spina bifida, Lancet 2:167. Brock DJH, Bolton AE, Monagham JM (1973) Prenatal diagnosis of anencephaly through maternal serum alpha-fetoprotein measurements. Lancet 2:923.

Maternal Serum Screening

413

Bundy AL, Saltzman DH, Pober B, Fine C, Emerson D, Doubilet PM (1986) Antenatal sonographic findings in Trisomy 18. J Ultrasound Med 5:361-364. Burton BK (1988) Elevated maternal serum alpha-fetoprotein (MSAFP): Interpretation and follow up. Clin Obstet Gynecol 31:293-305. Burton BK, Dillard RG, Clark EN (1985) Maternal serum ot-fetoprotein: The effect of participation on anxiety and attitude toward pregnancy in women with normal results. Am J Obstet Gynecol 152:540-543. Canick JA, Knight GJ (1992) Multiple marker screening for fetal Down syndrome. Contemp Obstet Gyn 36:25-42. Canick JA, Sailer DN (1993) Maternal serum screening for aneuploidy and open fetal defects. Obstet Gynecol Clin N Am 20:443-454. Canick JA, Knight GT, Palomaki GE, Haddow JE, Cuckle HS, Wald NJ (1988) Low second trimester maternal serum unconjugated estriol in pregnancies with Down syndrome. Br J Obstet Gynaecol 95:330-333. Canick JA, Palomaki GE, Osthanondh R (1990a) Prenatal screening for Trisomy 18 in the second trimester. Prenat Diagn 10:546. Canick JA, Panizza DS, Palomaki GE (1990b) Prenatal screening for Down syndrome using AFP, uE3 and hCG: Effect of maternal race, insulin dependent diabetes and twin pregnancy. Am J Hum Genet 47:A270. Casals E, Fortuny A, Grudzinskas, Suzuki Y, Teinser B, Comas C, Sanllehy C, Ojuel J, Borrell A, Soler A, Ballesta AM (1996) First trimester biochemical screening for Down syndrome with the use of PAPP-A, AFP and B-hCG. Prenat Diagn 16:405-410. Center for Disease Control and Prevention (CDC) (1992) Recommendations for the use of folic acid to reduce the number of cases of spina bifida and neural tube defects. MMWR 41:1-7. Cochrane DD, Wilson RD, Steinbok P, Farquharson DF, Irwin B, Irvine B, Chambers K (1996) Prenatal spinal evaluation and functional outcome of patients born with myelomeningocele: Information for improved prenatal counselling and outcome prediction. Fetal Diagn Ther 11:159-168. Cooley WC, Graham JM (1991) Down syndrome: An update for the primary pediatrician. Clin Pediat 30:233-253. Crandall BF, Matsumoto M (1991) Risks associated with elevated amniotic fluid a-fetoprotein level. AJMG 39:64-67. Crandall BF, Lebherz TB, Schroth PC, Matsumoto M (1983) Alpha-fetoprotein concentration in maternal serum: Relationship to race and body weight. Clin Chem 29:531. Crandall BF, Robinson L, Grau P (1991) Risks associated with an elevated maternal serum ct-fetoprotein level. Am J Obstet Gynecol 165:581-586. Cuckle HS, Wald NJ, Lindenbaum RH (1984) Maternal serum alpha-fetoprotein measurement: A screening test for Down syndrome. Lancet 1:926. Cuckle HS, Wald NJ (1987) The effect of estimating gestational age by ultrasound cephalometry on the sensitivity of alpha-fetoprotein screening for Down syndrome. Br J Obstet Gynaecol 94:274-276. David M, Israel N, Merksamer R, Bar-Nizan N, Borochowitz Z, Bar-el H, Yehudai I, Dar H (1995) Very low maternal serum unconjugated estriol and prenatal diagnosis of steroid sulfatase deficiency. Fetal Diagn Ther 10:76-79. Early KJ, Blanco JD, Prien S, Willis D (1991) Patient attitudes toward testing for maternal serum alpha-fetoprotein values when results are false-positive or true negative. SMJ 84:439-442. Elkins TE, Brown D (1993) The cost of choice: A price too high in the triple screen for Down syndrome. Clin Obstet Gynecol 36:532-540. Evans MI, Bottoms SF, Carlucci T, Grant J, Belsky RL, Solyom AE, Quiqq MH, LaFerla JJ (1988) Determinants of altered anxiety after abnormal maternal serum a-fetoprotein screening. Am J Obstet Gynecol 159:1501-1504. Faden RR, Chwalow AF, Orel-Crosby E, Holtzman, NA, Chase GA, Leonard CO (1985) What participants understand about a maternal serum alpha-fetoprotein screening program. AJPH 75:1381-1384.

414

Ormond

Farrant W (1980) Stress after amniocentesis for high serum alpha-fetoprotein concentrations. BMJ 281:452. Fearn J, Hibbard BM, Laurence KM, Roberts A, Robinson JO (1982) Screening for neural tube defects and maternal anxiety. Br J Obstet Gynaecol 218-221. Fejgin M, Amiel A, Goldberger S, Barnes I, Zer T, Kohn G (1992) Placental insufficiaency as a possible cause of low maternal serum human chorionic gonadotropin and low maternal serum unconjugated estriol in triploidy. Am J Obstet Gynecol 167:766-767. Feuchtbaum LB, Cunningham G, Waller K, Lustig LS, Tomkinson DG, Hook EB (1995) Fetal karyotyping for chromosome abnormalities after an unexplained elevated maternal serum alpha-fetoprotein screening. ObGyn 86:248. Green JM (1990) Prenatal screening and diagnosis: Some psychological and social issues. Br J Obstet Gynaecol 97:1074-1076. Green JM, Statham H (1996) Psychological aspects of prenatal screening and diagnosis. In: Marteau TM, Richards M (eds) The Troubled Helix: Social and Psychological Implications of the New Human Genetics. New York: Cambridge University Press, pp 140-163. Haddow JE, Palomaki GE, Knight GT, Williams J, Pulkkinen A, Canick JA, Sailer DN, Bowers GB (1992) Prenatal screening for Down syndrome with use of maternal serum markers. NEJM 327:588-593. Haddow JE, Palomaki GE, Knight GJ, Cunningham GC, Lustig LS, Boyd PA (1994) Reducing the need for amniocentesis in women 35 years of age or older with serum markers for screening. NEJM 330:1114-1118. Harmon JP, Hiett AK Palmer CG, Golichowski AM (1995) Prenatal ultrasound detection of isolated neural tube defects: Is cytogenetic evaluation warranted? ObGyn 86:595. Hill LM (1996) The sonographic detection of Trisomies 13, 18 and 21. Clin Obstet Gynecol 39:831-850. Hook EB, Mutton DE, Ide R, Alberman E, Bobrow M (1995) The natural history of Down syndrome conceptuses diagnosed prenatally that are not electively terminated. AJHG 57:875-881. Izumi H, Saito N, Ichiki S, Makino Y, Yukitake K, Kaneoka T (1993) Prenatal diagnosis of congenital lipoid adrenal hyperplasia. Obstet Gynecol 81:839-841. Jauniaux E, Brown R, Snijders RJM, Noble P, Nicolaides KH (1997) Early prenatal diagnosis of triploidy. Am J Obstet Gynecol 176:550-554. Keenan KL, Basso D, Goldkrand J, Butler WJ (1991) Low level of maternal serum alpha-fetoprotein: Its associated anxiety and the effects of genetic counseling. Am J Obstet Gynecol 54-56. Keren DF, Canick JA, Johnson MZ, Schaldenbrand JD, Haning RV, Jr., Hacket R (1995) Low maternal serum unconjugated estriol during prenatal screening as an indication of placental steroid sulfatase deficiency and X-linked ichthyosis. Am J Clin Pathol 103:400-403. Kidd J, Cook R, Marteau TM (1993) Is routine AFP screening in pregnancy reassuring? / Psychosomatic Res 37:717-722. Kolker A, Burke BM (1987) Amniocentesis and the Social Construct of Pregnancy. Hawthorne Press, pp 95-116. Knight GJ, Palomaki GE, Haddow JE (1988) Use of maternal serum alpha-fetoprotein measurements to screen for Down syndrome. Clin Obstet Gynecol 31:306-327. LeRoy BS (1993) When theory meets practice: Challenges to the field of genetic counseling. In: Bartels DM, LeRoy BS, Caplan AL (eds) Prescribing Our Future: Ethical Challenges in Genetic Counseling. New York: Walter de Gruyter, pp 39-56. Lockwood C, Benacerraf BR, Krinsky A, Blakemore K, Belanger K, Mahoney M, Hobbins J (1987) A sonographic screening method for Down syndrome. Am J Obstet Gynecol 157:803-808. Lowry DL, Campbell SA, Krivchenia E, Dvorin E, Duqette D, Evans MI (1995) Impact of abnormal second-trimester maternal serum dingle, double, and triple screening on patient choices about prenatal diagnosis. Fetal Diagn Ther 10:286-289. Luthy DA, Wardinsky T, Shurtleff DB, Hollenback KA, Hickok DE, Nyberg DA, Bendetti TJ (1991) Cesarean section before the onset of labor and subsequent motor function in infants with meningomyelocele diagnosed antenatally. NEJM 324:662-666.

Maternal Serum Screening

415

Maher JE, Davis RO, Goldenberg RL, Boots LR, DuBard MB (1994) Unexplained elevations in maternal serum alpha-fetoprotein and subsequent fetal loss. Obstet Gynecol 83:138-141. Marteau TM, Johnston M, Plenicar M, Shaw RW, Slack J (1988) Development of a self-administered questionnaire to measure women's knowledge of prenatal screening and diagnostic tests. / Psychosomat Res 32:403-408. Marteau TM, Johnston M, Shaw RW, Michie S, Kidd J, New M (1989) The impact of prenatal screening and diagnostic testing upon the cognitions, emotions and behaviours of pregnant women. J Psychosomat Res 33:7-16. Marteau TM, Kidd J, Cook R, Michie S, Johnston M, Slack J, Shaw RW (1991) Perceived risk not actual risk predicts uptake of amniocentesis. Br J Obstet Gynaecol 98:282-286. Marteau TM, Cook R, Kidd J, Michie S, Johnston M, Slack J, Shaw RW (1992a) The psychological effects of false-positive results in prenatal screening for fetal abnormality: A prospective study. Prenat Diagn 12:205-214. Marteau TM, Johnston M, Kidd J, Michie S, Cook R (1992b) Psychological models in predicting uptake of prenatal screening. Psychoi Health 6:13-22. Marteau TM, Kidd J, Michie S, Cook R, Johnston M, Shaw RW (1993) Anxiety, knowledge and satisfaction in women receiving false positive results on routine prenatal screening: A randomized controlled trial. J Psychosomat Obstet Gynaecol 14:185-196. Merkatz IR, Nitowski HM, Macri JN, Johnson WE (1984) An association between low maternal serum alpha-fetoprotein and fetal chromosome abnormality. Am } Obstet Gynecol 148:866. Michie S, Marteau T (1996) Genetic Counseling: Some issues of theory and practice. In: Marteau TM, Richards M (eds) The Troubled Helix: Social and Psychological Implications of the New Human Genetics. New York: Cambridge University Press, pp 104-122. Milunsky A, Allpert E, Kitzmiller JL, Youner M, Neff RK (1982) Prenatal diagnosis of neural tube defects Part VIII. The importance of serum alpha-fetoprotein screening in the diabetic pregnant woman. Am J Obstet Gynecol 142:1030. Milunsky A, Jick SS, Bruell CL, MacLaughlin DS, Tsung YK Jick H, Rothman KJ, Willett W (1989) Predictive values, relative risks, and overall benefits of high and low maternal serum a-fetoprotein screening in singleton pregnancies: New epidemiological data. Am J Obstet Gynecol 161:291-297. Mooney RA, Peterson CJ, French CA, Sailer DN, Arvan DA (1994) Effectiveness of combining maternal serum alpha-fetoprotein and hCG in a second trimester screening program for Down syndrome. Obstet Gynecol 84:298-303. Nadel AS, Green TR, Holmes LB, Frigoletto FD, Benacerraf BR (1990) Absence of need for amniocentesis in patients with elevated levels of maternal serum alpha-fetoprotein and normal ultrasonographic examinations. NEJM 323:557-561. NERGG Prenatal Collaborative Study of Down syndrome Screening (1989) Combining maternal serum a-fetoprotein measurements and age to screen for Down syndrome in pregnant women under age 35. Am J Obstet Gynecol 160:575-581. Neveux LM, Palomaki GE, Knight GJ, Haddow JE (1996) Multiple marker screening for Down syndrome in twin pregnancies. Prenat Diagn 16:29. Nyberg DA, Resta RG, Luthy DA, Hickok DE, Mahony BS, Hirsch JH (1990) Prenatal sonographic findings of Down syndrome: Review of 94 cases. Obstet Gynecol 76:370-377. Nyberg DA, Kramer D, Resta RG, et al. (1993) Prenatal sonographic findings of Trisomy 18: Review of 47 cases. J Ultrasound Med 2:103-113. Ormond KE, Pergament E, Fine BA (1996) Pre-screening education in multiple marker screening programs: The effect on patient anxiety and knowledge. JGC 5:69-80. Oyer CE, Canick JA (1992) Maternal serum hCG levels in triploidy: Variability and need to consider molar tissue. Prenat Diagn 12:627-628. Palomaki GE, Hill LE, Knight GJ, Haddow JE, Carpenter M (1988) Second-trimester maternal serum alpha-fetoprotein levels in pregnancies associated with gastroschisis and omphalocele. Obstet Gynecol 71:906-909. Palomaki GE, Knight GJ, Haddow JE, Canick JA, Sailer DN, Panizza DS (1992) Prospective intervention trial of a screening protocol to identify fetal Trisomy 18 using maternal alpha-fetoprotein, unconjugated estriol and human chorionic gonadotropin. Prenat Diagn 12:925-930.

416

Ormond

Palomaki GE, Knight GJ, McCarthy J, Haddow JE, Eckfeldt JH (1993) Maternal serum screening for fetal Down syndrome in the United States: A 1992 Survey. Obstet Gynecol 169:1558-1562. Palomaki GE, Haddow JE, Knight GJ, Wald NJ, Kennard A, Canick JA, Sailer DN, Blitzer MG, Dickerman LH, Fisher R, Hansmann D, Hansmann M, Luthy DA, Summers AM, and Wyatt P (1995) Risk based prenatal screening for Trisomy 18 using alpha-fetoprotein, unconjugated oestriol and human chorionic gonadotropin. Prenat Diagn 15:713-723. Pergament E, Stein AK, Fiddler M, Cho NH, Kupferminc MJ (1995) Adverse pregnancy outcome after a false positive screen for Down syndrome using multiple markers. ObGyn 86:255-258. Peter M, Partsch CJ, Dorr HG, Sippell WG (1996) Prenatal diagnosis of congenital adrenal hypoplasia. Hormone Res 46:41-45, Reynolds TM, Nix AM, Dunstan FD, Dawson AJ (1993) Age-Specific detection and false positive rates: An aid to counseling in Down syndrome risk screening. Obstet Gynecol 81:447-450. Robinson JO, Hibbard BM, Laurence KM (1984) Anxiety during a crisis: Emotional effects of screening for neural tube defects. / Psychosomat Res 28:163-169. Rossiter JP, Hofman KJ, Kelley RI (1995) Smith-Lemli-Opitz syndrome: Prenatal diagnosis by quantification of cholesterol precursors in amniotic fluid. Am J Med Genet 56:272-275. Ruiz-Bueno JB, Sime AM, Kitchell MH (1991) Effect of receiving genetic counseling on pre-event anxiety in genetic amniocentesis patients. Pre- Perinatal Psychol 6:171-179. Saenger P, Klonari Z, Black SM, Compagnone N, Mellon SH, Fleischer A, Abrams CA, Shackleton CH, Miller WL (1995) Prenatal diagnosis of congenital lipoid adrenal hyperplasia. J Clin Endocrinol Metabol 80:200-205. Santolaya-Forgas J, Jessup J, Burd LI, Prins GS, Burton BK (1996) Pregnancy outcome in women with low midtrimester maternal serum unconjugated estriol. J Reprod Med 41:87-90. Sepulveda W, Donaldson A, Johnson RD, Davies G, Fisk NM (1995) Are routine alpha-fetoprotein and acetylcholinesterase determinations still necessary at second trimester amniocentesis? Impact of high resolution ultrasonography. Obstet Gynecol 85:107. Standing Medical Advisory Committee (1979) Report by the Working Group on Screening for Neural Tube Defects. Douglas Black, Chairman, DHSS. Stiller RJ, Haynes de Regt R, Suntag S, Baumgarten A, Hobbins JC, Mahoney MJ (1990) Elevated maternal serum alpha-fetoprotein concentration and fetal chromosomal abnormalities. Obstet Gynecol 75:994-997. Thiagarajah S, Stroud CB, Vavelidis F, Schnorr JA, Schnatterly PT, Ferguson JE (1995) Elevated maternal serum ot-fetoprotein levels: What is the risk of fetal aneuploidy? Am J Obstet Gynecol 173:388-392. Thomas RL, Blakemore KJ (1990) Evaluation of elevations in maternal serum alphafetoprotein: A review. Obstet Gynecol Surv 45:269-280. Thornton JG, Hewison J, Lilford RJ, Vail A (1995) A randomized trial of three methods of giving information about prenatal testing. BMJ 311:1127-1130. Toriello HV, Higgins JV (1983) Occurrence of neural tube defects among first-, second-, and third degree relatives of probands: Results of a United States survey. Am J Med Genet 15:601-606. Tsoi MM, Hunter M, Pearce M, Chudleigh P, Campbell S (1987) Ultrasound scanning in women with raised serum alpha-fetoprotein: Short term psychological effect. 3 Psychosomat Res 31:35-39. Tymstra TJ, Bajema C, Beekhuis JR, Mantingh A (1991) Women's opinions on the offer and use of prenatal diagnosis. Prenat Diagn 11:893-898. Wald NJ, Cuckle HS (1977) Maternal serum AFP measurement in antenatal screening for anencephaly and spina bifida in early pregnancy: Report of the UK collaborative study on alpha-fetoprotein in relation to neural tube defects. Lancet 2:1323-1332. Wald N, Cuckle H, Boreham J, Stirrat G (1980) Small biparietal diameter of fetuses with spina bifida: Implications for antenatal screening. Br J Obstet Gynaecol 87:219-221.

Maternal Serum Screening

417

Wald NJ, Cuckle HS, Densem JW, Nanchalhal K, Royston P, Chard T, Haddow JE, Knight GJ, Palomaki GE, Canick JA (1988) Maternal serum screening for Down syndrome in early pregnancy. Br Med J 297:883-887. Wald NJ, Cuckle HS (1988) AFP and age screening for Down syndrome. Am J Med Genet 31:197-209. Wald N, Cuckle H, Wu T, George L (1991) Maternal serum unconjugated oestriol and human chorionic gonadotropin levels in twin pregnancies: Implications for screening for Down's syndrome. Br J Obstet Gynaecol 98:905. Wald NJ, Cuckle HS, Densem JW, Kennard A, Smith D (1992) Maternal serum screening for Down's syndrome: The effect of routine ultrasound scan determination of gestational age and adjustment for maternal weight. Br J Obstet Gynaecol 99:144-149. Wald NJ, Densem JW, Smith D, Klee GG (1994) Four marker serum screening for Down syndrome. Prenat Diagn 14:707-716. Wald NJ Kennard A, Hackshaw AK (1995) First trimester screening for Down syndrome. Prenat Diagn 15:1227-1240. Wald NJ, Smith D, Densem JW, Petterson K (1996) Serum screening for Down syndrome between 8 and 14 weeks of pregnancy. Br J Obsetet Gynaecol 103:407-412. Walters CP, McKinnon W (1993) Poor pregnancy outcome associated with elevated maternal serum alpha-fetoprotein in combination with increased risk for Down syndrome. Prenat Diagn 13:221. Wenstrom KD, Sipes SL, Williamson RA, Grant SS, Trawick DC, Estle LC (1992) Prediction of pregnancy outcome with single versus serial maternal serum a-fetoprotein tests. Am J Obstet Gynecol 167:1529-1533. Wenstrom KD, Owen J, Boots LR, DuBard MB (1994) Elevated second trimester human chorionic gonadotropin levels in association with poor pregnancy outcomes. Am J Obstet Gynecol 171:1038-1041. Wenstrom KD, Owen J, Davis RO, Brumfield CG (1996) Prognostic significance of unexplained elevated amniotic fluid alpha-fetoprotein. ObGyn 87:213-216. Zalel Y, Kedar I, Tepper R, Chen R, Drugan A, Fejgin M, Beyth Y (1996) Differential diagnosis and management of very low second trimester maternal serum unconjugated estiol levels, with special emphasis on the diagnosis of X-linked ichthyosis. Obstet Gynecol Surv 51(3):200-203.