AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 7, NUMBER 3
July 1990
AMNIOTIC FLUID INDEX: AN APPROPRIATE PREDICTOR OF PERINATAL OUTCOME Susan M. Shmoys, M.D., Miriam Sivkin, M.D., Carol Dery, R.N., Alan G. Monheit, M.D., and David A. Baker, M.D.
Qualitative amniotic fluid volume determination is a routine part of the fetal biophysical profile score. Quantitative amniotic fluid volume measurement, however, is not a factor in the determination of the standard biophysical profile score. This study is a retrospective analysis of antepartum assessment of amniotic fluid volumes and their relationship to neonatal outcomes. The amniotic fluid index was calculated for all patients examined and perinatal outcome was studied for all patients assessed. Patients with reduced or increased amniotic fluid volume had a significant increase in meconiumstained amniotic fluid, Apgar scores less than 7 at 1 and 5 minutes, major congenital anomalies, admission to the neonatal intensive care unit, and were more likely to require delivery by cesarean section for fetal distress. This study suggests that a quantitative ultrasound measurement of amniotic fluid volume represents an effective discriminatory test to be used in pregnancy evaluation.
Biophysical techniques for the determination of the fetal condition have afforded a significant contribution to the decline in perinatal morbidity and mortality during the last decade. Intrapartum fetal heart rate monitoring initially provided information concerning the fetal status; it was from these findings that antepartum fetal heart rate monitoring was then developed.1 In addition to these techniques, ultrasonography has now been enlisted to offer a more detailed and accurate assessment of the fetus and its intrauterine environment. The fetal biophysical profile (BPP) is a dynamic evaluation of fetal well-being comprised of both antepartum fetal heart rate testing and real-time ultrasound assessment.2 An important component of the BPP has been the evaluation of amniotic fluid volume and its relationship to fetal development and condition. Perinatal morbidity and mortality are thought to be significantly increased when polyhydramnios3 or oligohydramnios4 are present at delivery. In the performance of the BPP the qualitative amniotic fluid volume determination is based on the measurement of the largest pocket of amniotic fluid in two perpendicular planes. Manning and Platt5 have reported an increased incidence of intrauterine growth retardation and increased perinatal mortality in infants in whom the largest pocket of amniotic fluid measured
less than 1 cm; other researchers6 have found that a pocket less than 2 cm is correlated with poor outcome. Chamberlain et al7 in 1984 found that in patients with increased qualitative amniotic fluid volume the incidence of major congenital anomalies was also significantly higher. The BPP does not, however, include a quantitative measure of amniotic fluid volume, only a qualitative measurement. Phelan et al8 demonstrated a four-quadrant technique for assessing amniotic fluid volume, termed the amniotic fluid index (AFI). Studies evaluating the use of the AFI in predicting perinatal outcome are now in progress. The purpose of this study is to examine the efficacy of the AFI in patients being evaluated with BPP in order to assess whether the AFI is a better predictor of perinatal outcome than the qualitative amniotic fluid assessment currently performed. MATERIALS AND METHODS
The study population consisted of 237 highrisk patients with a singleton pregnancy referred for fetal BPP scoring at the University Hospital at Stony Brook, New York. The indications for testing are listed on Table 1. All patients with ruptured mem-
Department of Obstetrics and Gynecology, State University of New York at Stony Brook, Stony Brook, New York Reprint requests: Dr. Shmoys, Dept. Obstetrics & Gynecology, HSC, T-9, Room 080, S.U.N.Y., Stony Brook, NY 11794 266
Copyright © 1990 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
Downloaded by: University of Pennsylvania Libraries. Copyrighted material.
ABSTRACT
AMNIOT1C FLUID INDEX/Shmoys, Sivkin, Dery, et al.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
Postdatism Preeclampsia Premature labor Rule out intrauterine growth retardation Gestational diabetes Rule out polyhydramnios Hypertension Advanced maternal age Insulin-dependent diabetes mellitus Decreased fetal movement Bleeding Rule out oligohydramnios Previous perinatal loss Asthma Drug abuse
No.
%
68 31 30 23
28.7 13.0 12.7
21 13 8 7 7 7 7 6 4 4 1
8.9 5.5 3.3 3.0 3.0 3.0 3.0 2.5 1.7 1.7 0.4
9.7
branes or with fetal death recognized at the time of initial referral were excluded from the study population. The study period was from November, 1987, to March, 1988, inclusively. BPP scoring, including qualitative amniotic fluid volume determinations, were performed at least weekly until delivery in the referred population. Patients underwent a fourquadrant assessment of amniotic fluid volume, thus enabling a determination of their AFI to be calculated. The mean number of tests per patient was 2.8 (range, 1 to 10). The final study performed within 1 week of delivery was used for comparison to the outcome of the pregnancy. The nonstress test was the first parameter evaluated. The patient was maintained in a semi-Fowler position during this test, which utilized a Corometrics Model #115 to record fetal heart rate and movements. If a nonreactive pattern continued for 40 minutes from the initiation of the testing, the test was defined as nonreactive. All patients then had both a BPP and an AFI evaluation. The ultrasonographic evaluation, performed with an ATL UltraMark IV, consisted of a 30-minute examination period during which time adequate fetal movements and fetal breathing movements were identified and fetal tone and amniotic fluid volume (using a 2 cm pocket minimum) were assessed. Each biophysical variable was assigned a score of 2 if normal or zero if abnormal. To perform the amniotic fluid evaluation, the patient was maintained in a semi-Fowler position. The AFI was performed according to Phelan et al.8 The normal AFI was based on the work of Phelan et al,9 which defined oligohydramnios as an AFI less than or equal to 5 cm and polyhydramnios as an AFI greater than 20 cm. All testing was performed by specially trained antepartum nurses. Abnormal scans were all confirmed by the obstetric residents or attending staff. The patients were then managed according to standard obstetric protocols. Pregnancy outcome was assessed by the incidence of the following: fetal heart rate abnormalities that required emergent cesarean section; the presence or absence of moderate or thick
meconium; Apgar scores of less than 7 at 1 and 5 minutes; late or persistent severe variable decelerations; fetal acidosis (cord pH with venous and arterial measurements of less than 7.20); admission to the neonatal intensive care unit (NICU); congenital anomalies; and perinatal mortality. Statistical analysis was performed utilizing the chi-square test. RESULTS
The BPP performed included scores with points deducted for nonreactive nonstress tests, absence of fetal breathing, and inadequate fluid as defined by the "2 centimeter pocket" rule. All patients were noted to have had adequate fetal tone and movement during their testing. Nonreactive nonstress tests were present in 13 of 237 (5.5%). Absent fetal breathing was observed in 6 of 237 (2.5%). Inadequate fluid was identified in 4 of 237 (1.7%) utilizing the above definition. However, when evaluated by the AFI, 98 of 237 (41.4%) had inadequate fluid (that is, less than or equal to 5 cm). The remaining patients were distributed as follows: 38 of the patients (16.0%) had polyhydramnios and only 101 of the patients (42.6%) had normal amniotic fluid volume. The perinatal outcome was correlated with the final BPP examination performed prior to delivery. The relationship between perinatal outcome and the AFI was similarly assessed. Of those patients with a normal AFI, 1 (1%) had thick meconium; 1 (1%) had late or persistent severe variable decelerations; 1 (1%) required an emergent cesarean section; none had Apgar scores of less than 7; 5 (5%) had a cord pH less than 7.20; and 2 (2%) neonates required NICU admission. When examining the four patients who did not have adequate fluid on their BPP assessment, two had thick meconium, late decelerations, and underwent primary cesarean sections for fetal indications (an incidence of 50%); 1 (25%) had a cord pH of less than 7.20; and none of these neonates had a congenital anomaly or experienced perinatal mortality. There were seven patients with fetuses that had a variety of congenital anomalies among the 237 patients initially entered into the study. None of these were identified prior to referral to the Antepartum Testing Unit. None of the pregnancies with a normal AFI resulted in infants with congenital anomalies; four of the seven patients with congenital anomalies had elevated AFIs and the other three had decreased AFIs. There were five perinatal deaths in the study population. Three of the five deaths occurred in pregnancies with an elevated AFI; the other two were among those with a low AFI. No deaths occurred in any pregnancy with a normal AFI. Congenital anomalies were responsible for four of the five perinatal deaths. All of the pregnancies that resulted in perinatal deaths or congenital anomalies received normal scores of 2 on their BPP for fluid volume assessment. 267
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Table 1. Indications for Antepartum Testing
AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 7, NUMBER 3 July 1990 Perinatal Outcome with a Low AFI Decreased AFI (n = 98) Complication Thick meconium Decelerations Emergent cesarean section Apgar less than 7 at 5 minutes Fetal acidosis NICU admission Congenital anomalies Perinatal deaths
17.4 41.8 15.3 5.1 19.4 24.5 3.1 2.1
A comparison was made between the normal controls and those with a decreased AFI for the previously described study parameters (Table 2). In the group of patients with a low AFI, the incidence of thick meconium was 17.4% (17 of 98). The rates for late or persistent severe variable decelerations and emergent cesarean sections were 41.8% (41 of 98) and 15.3% (15 of 98), respectively. Five-minute Apgar scores were less than 7 in 5.1% (5 of 98) and the cord pH was less than 7.20 in 19.4% (19 of 98). Among those patients with a low AFI, the neonate required admission to the NICU in 24.5% (24 of 98). With the exception of the 5-minute Apgar score, when these findings were compared with the control group with a normal AFI, the differences were statistically significant at p < 0.001. A similar comparison was made between the group with an increased AFI and the normal controls (Table 3). This aspect of the study revealed that of those pregnancies with an elevated AFI, thick meconium was present in 26.3% (10 of 38). Late or persistent severe variable decelerations were present in 44.7% (17 of 38) and emergent cesarean sections were performed in 36.8% (14 of 38). Five-minute Apgar scores were less than 7 in 23.7% (9 of 38) and the cord pH was less than 7.20 in 36.8% (14 of 38). Among those patients with an elevated AFI, the neonate required admission to the NICU in 42.1% (16 of 38). When these findings were compared with the control group with a normal AFI, the differences were statistically significant at p < 10~6. Perinatal mortality was also significantly increased in the group with an elevated AFI, although not when corrected for congenital anomalies.
Table 3.
17 41 15 5 19 24 3 2
Complication
268
No.
July 1990
AMNIOTIC FLUID INDEX: AN APPROPRIATE PREDICTOR OF PERINATAL OUTCOME Susan M. Shmoys, M.D., Miriam Sivkin, M.D., Carol Dery, R.N., Alan G. Monheit, M.D., and David A. Baker, M.D.
Qualitative amniotic fluid volume determination is a routine part of the fetal biophysical profile score. Quantitative amniotic fluid volume measurement, however, is not a factor in the determination of the standard biophysical profile score. This study is a retrospective analysis of antepartum assessment of amniotic fluid volumes and their relationship to neonatal outcomes. The amniotic fluid index was calculated for all patients examined and perinatal outcome was studied for all patients assessed. Patients with reduced or increased amniotic fluid volume had a significant increase in meconiumstained amniotic fluid, Apgar scores less than 7 at 1 and 5 minutes, major congenital anomalies, admission to the neonatal intensive care unit, and were more likely to require delivery by cesarean section for fetal distress. This study suggests that a quantitative ultrasound measurement of amniotic fluid volume represents an effective discriminatory test to be used in pregnancy evaluation.
Biophysical techniques for the determination of the fetal condition have afforded a significant contribution to the decline in perinatal morbidity and mortality during the last decade. Intrapartum fetal heart rate monitoring initially provided information concerning the fetal status; it was from these findings that antepartum fetal heart rate monitoring was then developed.1 In addition to these techniques, ultrasonography has now been enlisted to offer a more detailed and accurate assessment of the fetus and its intrauterine environment. The fetal biophysical profile (BPP) is a dynamic evaluation of fetal well-being comprised of both antepartum fetal heart rate testing and real-time ultrasound assessment.2 An important component of the BPP has been the evaluation of amniotic fluid volume and its relationship to fetal development and condition. Perinatal morbidity and mortality are thought to be significantly increased when polyhydramnios3 or oligohydramnios4 are present at delivery. In the performance of the BPP the qualitative amniotic fluid volume determination is based on the measurement of the largest pocket of amniotic fluid in two perpendicular planes. Manning and Platt5 have reported an increased incidence of intrauterine growth retardation and increased perinatal mortality in infants in whom the largest pocket of amniotic fluid measured
less than 1 cm; other researchers6 have found that a pocket less than 2 cm is correlated with poor outcome. Chamberlain et al7 in 1984 found that in patients with increased qualitative amniotic fluid volume the incidence of major congenital anomalies was also significantly higher. The BPP does not, however, include a quantitative measure of amniotic fluid volume, only a qualitative measurement. Phelan et al8 demonstrated a four-quadrant technique for assessing amniotic fluid volume, termed the amniotic fluid index (AFI). Studies evaluating the use of the AFI in predicting perinatal outcome are now in progress. The purpose of this study is to examine the efficacy of the AFI in patients being evaluated with BPP in order to assess whether the AFI is a better predictor of perinatal outcome than the qualitative amniotic fluid assessment currently performed. MATERIALS AND METHODS
The study population consisted of 237 highrisk patients with a singleton pregnancy referred for fetal BPP scoring at the University Hospital at Stony Brook, New York. The indications for testing are listed on Table 1. All patients with ruptured mem-
Department of Obstetrics and Gynecology, State University of New York at Stony Brook, Stony Brook, New York Reprint requests: Dr. Shmoys, Dept. Obstetrics & Gynecology, HSC, T-9, Room 080, S.U.N.Y., Stony Brook, NY 11794 266
Copyright © 1990 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
Downloaded by: University of Pennsylvania Libraries. Copyrighted material.
ABSTRACT
AMNIOT1C FLUID INDEX/Shmoys, Sivkin, Dery, et al.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
Postdatism Preeclampsia Premature labor Rule out intrauterine growth retardation Gestational diabetes Rule out polyhydramnios Hypertension Advanced maternal age Insulin-dependent diabetes mellitus Decreased fetal movement Bleeding Rule out oligohydramnios Previous perinatal loss Asthma Drug abuse
No.
%
68 31 30 23
28.7 13.0 12.7
21 13 8 7 7 7 7 6 4 4 1
8.9 5.5 3.3 3.0 3.0 3.0 3.0 2.5 1.7 1.7 0.4
9.7
branes or with fetal death recognized at the time of initial referral were excluded from the study population. The study period was from November, 1987, to March, 1988, inclusively. BPP scoring, including qualitative amniotic fluid volume determinations, were performed at least weekly until delivery in the referred population. Patients underwent a fourquadrant assessment of amniotic fluid volume, thus enabling a determination of their AFI to be calculated. The mean number of tests per patient was 2.8 (range, 1 to 10). The final study performed within 1 week of delivery was used for comparison to the outcome of the pregnancy. The nonstress test was the first parameter evaluated. The patient was maintained in a semi-Fowler position during this test, which utilized a Corometrics Model #115 to record fetal heart rate and movements. If a nonreactive pattern continued for 40 minutes from the initiation of the testing, the test was defined as nonreactive. All patients then had both a BPP and an AFI evaluation. The ultrasonographic evaluation, performed with an ATL UltraMark IV, consisted of a 30-minute examination period during which time adequate fetal movements and fetal breathing movements were identified and fetal tone and amniotic fluid volume (using a 2 cm pocket minimum) were assessed. Each biophysical variable was assigned a score of 2 if normal or zero if abnormal. To perform the amniotic fluid evaluation, the patient was maintained in a semi-Fowler position. The AFI was performed according to Phelan et al.8 The normal AFI was based on the work of Phelan et al,9 which defined oligohydramnios as an AFI less than or equal to 5 cm and polyhydramnios as an AFI greater than 20 cm. All testing was performed by specially trained antepartum nurses. Abnormal scans were all confirmed by the obstetric residents or attending staff. The patients were then managed according to standard obstetric protocols. Pregnancy outcome was assessed by the incidence of the following: fetal heart rate abnormalities that required emergent cesarean section; the presence or absence of moderate or thick
meconium; Apgar scores of less than 7 at 1 and 5 minutes; late or persistent severe variable decelerations; fetal acidosis (cord pH with venous and arterial measurements of less than 7.20); admission to the neonatal intensive care unit (NICU); congenital anomalies; and perinatal mortality. Statistical analysis was performed utilizing the chi-square test. RESULTS
The BPP performed included scores with points deducted for nonreactive nonstress tests, absence of fetal breathing, and inadequate fluid as defined by the "2 centimeter pocket" rule. All patients were noted to have had adequate fetal tone and movement during their testing. Nonreactive nonstress tests were present in 13 of 237 (5.5%). Absent fetal breathing was observed in 6 of 237 (2.5%). Inadequate fluid was identified in 4 of 237 (1.7%) utilizing the above definition. However, when evaluated by the AFI, 98 of 237 (41.4%) had inadequate fluid (that is, less than or equal to 5 cm). The remaining patients were distributed as follows: 38 of the patients (16.0%) had polyhydramnios and only 101 of the patients (42.6%) had normal amniotic fluid volume. The perinatal outcome was correlated with the final BPP examination performed prior to delivery. The relationship between perinatal outcome and the AFI was similarly assessed. Of those patients with a normal AFI, 1 (1%) had thick meconium; 1 (1%) had late or persistent severe variable decelerations; 1 (1%) required an emergent cesarean section; none had Apgar scores of less than 7; 5 (5%) had a cord pH less than 7.20; and 2 (2%) neonates required NICU admission. When examining the four patients who did not have adequate fluid on their BPP assessment, two had thick meconium, late decelerations, and underwent primary cesarean sections for fetal indications (an incidence of 50%); 1 (25%) had a cord pH of less than 7.20; and none of these neonates had a congenital anomaly or experienced perinatal mortality. There were seven patients with fetuses that had a variety of congenital anomalies among the 237 patients initially entered into the study. None of these were identified prior to referral to the Antepartum Testing Unit. None of the pregnancies with a normal AFI resulted in infants with congenital anomalies; four of the seven patients with congenital anomalies had elevated AFIs and the other three had decreased AFIs. There were five perinatal deaths in the study population. Three of the five deaths occurred in pregnancies with an elevated AFI; the other two were among those with a low AFI. No deaths occurred in any pregnancy with a normal AFI. Congenital anomalies were responsible for four of the five perinatal deaths. All of the pregnancies that resulted in perinatal deaths or congenital anomalies received normal scores of 2 on their BPP for fluid volume assessment. 267
Downloaded by: University of Pennsylvania Libraries. Copyrighted material.
Table 1. Indications for Antepartum Testing
AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 7, NUMBER 3 July 1990 Perinatal Outcome with a Low AFI Decreased AFI (n = 98) Complication Thick meconium Decelerations Emergent cesarean section Apgar less than 7 at 5 minutes Fetal acidosis NICU admission Congenital anomalies Perinatal deaths
17.4 41.8 15.3 5.1 19.4 24.5 3.1 2.1
A comparison was made between the normal controls and those with a decreased AFI for the previously described study parameters (Table 2). In the group of patients with a low AFI, the incidence of thick meconium was 17.4% (17 of 98). The rates for late or persistent severe variable decelerations and emergent cesarean sections were 41.8% (41 of 98) and 15.3% (15 of 98), respectively. Five-minute Apgar scores were less than 7 in 5.1% (5 of 98) and the cord pH was less than 7.20 in 19.4% (19 of 98). Among those patients with a low AFI, the neonate required admission to the NICU in 24.5% (24 of 98). With the exception of the 5-minute Apgar score, when these findings were compared with the control group with a normal AFI, the differences were statistically significant at p < 0.001. A similar comparison was made between the group with an increased AFI and the normal controls (Table 3). This aspect of the study revealed that of those pregnancies with an elevated AFI, thick meconium was present in 26.3% (10 of 38). Late or persistent severe variable decelerations were present in 44.7% (17 of 38) and emergent cesarean sections were performed in 36.8% (14 of 38). Five-minute Apgar scores were less than 7 in 23.7% (9 of 38) and the cord pH was less than 7.20 in 36.8% (14 of 38). Among those patients with an elevated AFI, the neonate required admission to the NICU in 42.1% (16 of 38). When these findings were compared with the control group with a normal AFI, the differences were statistically significant at p < 10~6. Perinatal mortality was also significantly increased in the group with an elevated AFI, although not when corrected for congenital anomalies.
Table 3.
17 41 15 5 19 24 3 2
Complication
268
No.
