Letters
Volume 163 Number 3
corticotropin-releasing hormone may be a stimulator of maternal pituitary adrenocorticotropic hormone secretion in humans. J Clin Invest 1989;84:1997-2001. 4. Sano T, Saito H, Yamasaki R, et al. Immunoreactivity against anti-growth hormone-releasing hormone (GHRH) sera in human pancreas and pancreatic endocrine tumors: evidence of pitfall in immunohistochemical study. Biomed Res 1987;8:407-14.
Ultrasonographic dating of very early pregnancy
To the Editors: How does one date a normal singleton intrauterine pregnancy ultrasonographically before detection of the crown-rump length l or early fetal cardiac activit y2? We attempted to answer this question in 1984 by relating the mean gestational age to mean sac diameter.' Since then we have used the following simple formula 4 for dating several hundred early normal singleton intrauterine pregnancies and have found it to be reliable and useful with mean sac diameters :s 15 mm by either transabdominaF·' or transvaginal techniques: Mean gestational age in days = 30 + Mean sac diameter in millimeters (i.e., 5 mm sac = 35 days). The 95% confidence limits are ± 3 days, assuming the pregnancy is normal. The mean gestational age is menstrual age (conceptional age + 2 weeks). The mean sac diameter is obtained by averaging the length, width, and depth on perpendicular ultrasonograms through the largest portion of the gestational sac. All measurements should be from sac-fluid to fluid-sac interfaces. 2. 3 Alan V. Cadkin, MD, and Jacquelin McAlpin-Cadkin, RT, RDMS
1103
ered variables. Furthermore, a cross-sectional/longitudinal approach based on percentages of body fat versus level of exercise over a 24-month period would provide data on changes of body fat and levels of exercise before and during pregnancy versus outcome. In this way control over possible experimental bias would be increased. Because the reliability of uncollaborated selfreporting has been shown to be low, efforts should be made to collaborate all reports of duration and intensity of exercise per day. Further strength of design can be accomplished by controlling variances in diet. Records of quality and quantity of calories consumed during every 24-hour period would provide another axis of data by which possible dietary influences on pregnancy outcome may be made apparent. Another possible effect may lie in unaccounted for physiologic changes that can occur when a usually active woman ceases all forms of exercise when she becomes pregnant. Thus a comparison between exercise before and during pregnancy, exercise before but not during pregnancy, and pregnancy outcome would be useful. As Americans become more health conscious, the question of the effects of exercise, one's overall health, and pregnancy outcome will become increasingly important. Continuation of the author's research in this area is certainly warranted and welcomed. David K. Suzuki and Gaylon Miller clo Box 15, Cleveland Chiropractic College, 6401 Rockhill Road, Kansas City, MO 64131
Response declined
Diagnostic Ultrasound, 55 East Washington, Suite 1531, Chicago, IL 60602
REFERENCES 1. Robinson HP, Fleming JEE. A critical evaluation of sonar crown-rump length measurements. Br J Obstet Gynaecol 1975;82:702-10. 2. Cadkin AV, McAlpin J. Detection of fetal cardiac activity between 41 and 43 days of gestation. J Ultrasound Med 1984;3:499-503. 3. Cadkin AV, McAlpin J. The decidua-chorionic sac: a reliable sonographic indicator of intrauterine pregnancy prior to detection of a fetal pole. J Ultrasound Med 1984;3:53948. 4. Nyberg DA, Filly RA, Mahony BS, et al. Early gestation: correlation of hCG levels and sonographic identification. AJR 1985;144:951-4.
Maternal exercise and early pregnancy outcome
To the Editor: We enjoyed the article by Dr. Clapp on maternal exercise and early pregnancy outcome (Clapp 1F. The effects of maternal exercise on early pregnancy outcome. AM1 OBSTET GVNECOL 1989;161:1453-7). It adds to the growing body of literature that supports the position that judicious antigravitational exercise before and during pregnancy does not adversely affect outcome. We agree that the power of his experimental design would increase with wider representation of the populace. Cross-cultural parameters may also be consid-
Normal amniotic pressure in oligohydramnios after preterm rupture of membranes
To the Editors: In their article on amniotic pressure in oligohydramnios (Nicolini U, Fisk NM, Rodeck CH, Talbert DG, Wigglesworth 1S. Low amniotic pressure in oligohydramnios-Is this the cause of pUlmonary hypoplasia? AM J OBSTET GVNECOLI989;161:109810 I), Nicolini et al. propose low amniotic pressure as a possible mechanism contributing to lung hypoplasia in pregnancies complicated by reduced liquor volume. They also state that they have not measured the intraamniotic pressure in cases of oligohydramnios as a result of premature rupture of the membranes. We have performed pressure measurements in three pregnancies complicated by early rupture of membranes and resultant oligohydramnios with a fluid-filled system and a solid-state pressure transducer. Intraamniotic pressures are zeroed to the top of the maternal abdomen. The intraamniotic pressures were recorded before and after the infusion of200 ml of Hartmann's solution into the amniotic cavity to facilitate ultrasonographic visualization of the fetus. In the first case in which liquor was draining for 2 weeks before the procedure at 20 weeks, the intraamniotic pressure was 12 mm Hg. Preterm labor occurred at 29 weeks and a male infant weighing 1425 gm was delivered. He died of respira-
11 04
Letters
tory failure at 43 days after a stormy neonatal course; autopsy was refused. The other two cases involved preterm rupture of membranes at 21 and 22 weeks, respectively. In the former, intraamniotic pressure was 3 mm Hg. The baby was delivered at 36 weeks and 3 days, and had an uncomplicated postnatal period. The pressures in the last case were 9 mm Hg before and 10 mm Hg after infusion, and this pregnancy resulted in preterm labor at 31 weeks' gestation. The infant died in the neonatal period and autopsy confirmed pulmonary hypoxemia. According to published data, 1.2 the intramniotic pressures in these cases were within the normal range. Nicolini et al. suggest that the low pressure in oligohydramnios contributes to pulmonary hypoplasia by allowing intrapulmonary fluid to escape from the lungs down a pressure gradient. In these cases with normal intraamniotic pressure, this is unlikely to be a mechanism, particularly in the first case in which the pressure was at the upper limit of normal. Possibly the higher intraamniotic pressure is a factor in the genesis of preterm ruptured membranes. The first infant died of chronic lung disease. This could have been caused by prematurity alone, but the high level of respiratory support required, and the difficulties encountered in ventilating him, were thought to be a result of bronchopulmonary dysplasia. The mechanism of pulmonary hypoplasia remains unclear, but we have demonstrated that oligohydramnios per se is not always associated with low amniotic pressure. However, oligohydramnios, regardless of cause, is associated with respiratory problems in the neonatal period. Clinicians therefore need to look beyond amniotic pressure for the cause of pulmonary hypoplasia. Pam Johnson, MBBS, and Darryl J. Maxwell, MBBS Fetal Medicine Unit, Department of Obstetrics, Guy's Hospital, London, England SEI 9RT
REFERENCES 1. Nicolini U, Fisk NM, Talbert DG, et al. Intrauterine manometry: technique and application to fetal pathology. Prenat Diagn 1989;9:243-54. 2. Weiner CP, Heilskov J, Pelzer G, Grant S, Wenstrom K, Williamson RA. Normal values for human umbilical venous and amniotic fluid pressures and their alteration by fetal disease. AMJ OBSTET GYNECOLI989;161:7l4-7.
Reply To the Editors: We thank Drs. Johnson and Maxwell for their interest in our hypothesis on the pathogenesis of pulmonary hypoplasia. On the basis of three observations, they claim that oligohydramnios is not always associated with low amniotic pressure. This does not surprise us. In our recent series,1 although all 24 cases of severe oligohydramnios (deepest pool
Volume 163 Number 3
corticotropin-releasing hormone may be a stimulator of maternal pituitary adrenocorticotropic hormone secretion in humans. J Clin Invest 1989;84:1997-2001. 4. Sano T, Saito H, Yamasaki R, et al. Immunoreactivity against anti-growth hormone-releasing hormone (GHRH) sera in human pancreas and pancreatic endocrine tumors: evidence of pitfall in immunohistochemical study. Biomed Res 1987;8:407-14.
Ultrasonographic dating of very early pregnancy
To the Editors: How does one date a normal singleton intrauterine pregnancy ultrasonographically before detection of the crown-rump length l or early fetal cardiac activit y2? We attempted to answer this question in 1984 by relating the mean gestational age to mean sac diameter.' Since then we have used the following simple formula 4 for dating several hundred early normal singleton intrauterine pregnancies and have found it to be reliable and useful with mean sac diameters :s 15 mm by either transabdominaF·' or transvaginal techniques: Mean gestational age in days = 30 + Mean sac diameter in millimeters (i.e., 5 mm sac = 35 days). The 95% confidence limits are ± 3 days, assuming the pregnancy is normal. The mean gestational age is menstrual age (conceptional age + 2 weeks). The mean sac diameter is obtained by averaging the length, width, and depth on perpendicular ultrasonograms through the largest portion of the gestational sac. All measurements should be from sac-fluid to fluid-sac interfaces. 2. 3 Alan V. Cadkin, MD, and Jacquelin McAlpin-Cadkin, RT, RDMS
1103
ered variables. Furthermore, a cross-sectional/longitudinal approach based on percentages of body fat versus level of exercise over a 24-month period would provide data on changes of body fat and levels of exercise before and during pregnancy versus outcome. In this way control over possible experimental bias would be increased. Because the reliability of uncollaborated selfreporting has been shown to be low, efforts should be made to collaborate all reports of duration and intensity of exercise per day. Further strength of design can be accomplished by controlling variances in diet. Records of quality and quantity of calories consumed during every 24-hour period would provide another axis of data by which possible dietary influences on pregnancy outcome may be made apparent. Another possible effect may lie in unaccounted for physiologic changes that can occur when a usually active woman ceases all forms of exercise when she becomes pregnant. Thus a comparison between exercise before and during pregnancy, exercise before but not during pregnancy, and pregnancy outcome would be useful. As Americans become more health conscious, the question of the effects of exercise, one's overall health, and pregnancy outcome will become increasingly important. Continuation of the author's research in this area is certainly warranted and welcomed. David K. Suzuki and Gaylon Miller clo Box 15, Cleveland Chiropractic College, 6401 Rockhill Road, Kansas City, MO 64131
Response declined
Diagnostic Ultrasound, 55 East Washington, Suite 1531, Chicago, IL 60602
REFERENCES 1. Robinson HP, Fleming JEE. A critical evaluation of sonar crown-rump length measurements. Br J Obstet Gynaecol 1975;82:702-10. 2. Cadkin AV, McAlpin J. Detection of fetal cardiac activity between 41 and 43 days of gestation. J Ultrasound Med 1984;3:499-503. 3. Cadkin AV, McAlpin J. The decidua-chorionic sac: a reliable sonographic indicator of intrauterine pregnancy prior to detection of a fetal pole. J Ultrasound Med 1984;3:53948. 4. Nyberg DA, Filly RA, Mahony BS, et al. Early gestation: correlation of hCG levels and sonographic identification. AJR 1985;144:951-4.
Maternal exercise and early pregnancy outcome
To the Editor: We enjoyed the article by Dr. Clapp on maternal exercise and early pregnancy outcome (Clapp 1F. The effects of maternal exercise on early pregnancy outcome. AM1 OBSTET GVNECOL 1989;161:1453-7). It adds to the growing body of literature that supports the position that judicious antigravitational exercise before and during pregnancy does not adversely affect outcome. We agree that the power of his experimental design would increase with wider representation of the populace. Cross-cultural parameters may also be consid-
Normal amniotic pressure in oligohydramnios after preterm rupture of membranes
To the Editors: In their article on amniotic pressure in oligohydramnios (Nicolini U, Fisk NM, Rodeck CH, Talbert DG, Wigglesworth 1S. Low amniotic pressure in oligohydramnios-Is this the cause of pUlmonary hypoplasia? AM J OBSTET GVNECOLI989;161:109810 I), Nicolini et al. propose low amniotic pressure as a possible mechanism contributing to lung hypoplasia in pregnancies complicated by reduced liquor volume. They also state that they have not measured the intraamniotic pressure in cases of oligohydramnios as a result of premature rupture of the membranes. We have performed pressure measurements in three pregnancies complicated by early rupture of membranes and resultant oligohydramnios with a fluid-filled system and a solid-state pressure transducer. Intraamniotic pressures are zeroed to the top of the maternal abdomen. The intraamniotic pressures were recorded before and after the infusion of200 ml of Hartmann's solution into the amniotic cavity to facilitate ultrasonographic visualization of the fetus. In the first case in which liquor was draining for 2 weeks before the procedure at 20 weeks, the intraamniotic pressure was 12 mm Hg. Preterm labor occurred at 29 weeks and a male infant weighing 1425 gm was delivered. He died of respira-
11 04
Letters
tory failure at 43 days after a stormy neonatal course; autopsy was refused. The other two cases involved preterm rupture of membranes at 21 and 22 weeks, respectively. In the former, intraamniotic pressure was 3 mm Hg. The baby was delivered at 36 weeks and 3 days, and had an uncomplicated postnatal period. The pressures in the last case were 9 mm Hg before and 10 mm Hg after infusion, and this pregnancy resulted in preterm labor at 31 weeks' gestation. The infant died in the neonatal period and autopsy confirmed pulmonary hypoxemia. According to published data, 1.2 the intramniotic pressures in these cases were within the normal range. Nicolini et al. suggest that the low pressure in oligohydramnios contributes to pulmonary hypoplasia by allowing intrapulmonary fluid to escape from the lungs down a pressure gradient. In these cases with normal intraamniotic pressure, this is unlikely to be a mechanism, particularly in the first case in which the pressure was at the upper limit of normal. Possibly the higher intraamniotic pressure is a factor in the genesis of preterm ruptured membranes. The first infant died of chronic lung disease. This could have been caused by prematurity alone, but the high level of respiratory support required, and the difficulties encountered in ventilating him, were thought to be a result of bronchopulmonary dysplasia. The mechanism of pulmonary hypoplasia remains unclear, but we have demonstrated that oligohydramnios per se is not always associated with low amniotic pressure. However, oligohydramnios, regardless of cause, is associated with respiratory problems in the neonatal period. Clinicians therefore need to look beyond amniotic pressure for the cause of pulmonary hypoplasia. Pam Johnson, MBBS, and Darryl J. Maxwell, MBBS Fetal Medicine Unit, Department of Obstetrics, Guy's Hospital, London, England SEI 9RT
REFERENCES 1. Nicolini U, Fisk NM, Talbert DG, et al. Intrauterine manometry: technique and application to fetal pathology. Prenat Diagn 1989;9:243-54. 2. Weiner CP, Heilskov J, Pelzer G, Grant S, Wenstrom K, Williamson RA. Normal values for human umbilical venous and amniotic fluid pressures and their alteration by fetal disease. AMJ OBSTET GYNECOLI989;161:7l4-7.
Reply To the Editors: We thank Drs. Johnson and Maxwell for their interest in our hypothesis on the pathogenesis of pulmonary hypoplasia. On the basis of three observations, they claim that oligohydramnios is not always associated with low amniotic pressure. This does not surprise us. In our recent series,1 although all 24 cases of severe oligohydramnios (deepest pool
