412 spa Abstracts

500 A LONGITlIIINAL STlOY EVALUATING THE EFFECT OF GESTATIONAL AGE ON ANTENATAL ASSESSMENT TESTS. S.J. Carlan, M. Gore', S. VanMeter', o Mastrogiannis,U of S Fl,Oepts Ob/Gyn T"""",FL, ORMC,Orlando,FL

The purpose of th; s study was to eva 1 uate the effect of gestational age on antenatal assessment tests using the same group of patients throughout their pregnancy. Fourteen normal pregnant women with normal fetuses were studied every two weeks from 20 wks until delivery. Gestational ages were confirmed by early exam and ultrasound. A biophysical profile (SPP) and non­stress test (NST) were performed in the standard manner at each visit. Unbi 1 ical artery SID ratios (S/D) were obtained using a continuous wave doppler and were recorded during fetal apnea. A startle reflex was considered positive if a quiet fetus was demonstrated to startle on real time ultrasound within one second of a three second appl ication of sound using the stanc!ard artificial larynx. A vibrocoustic stilllJlation (VAS) was considered positive if a simi lar sound challenge resul ted in a >15 beat per minute increase in fetal heart rate for >15 seconds. All maternal and neonatal outcomes were normal. The mean birth weight was 3569 1 169 grams. ilKS BPP SO NST VAS STARTLE

%>6 Mean ±1S0 (% reae) (% reae) ~ 20 21 4.1 1 .7 0 0 0 22 14 4.01.7 0 14 0 24 36 3.8 1 1. 0 7 14 0 26 86 3.4 1 .7 57 29 0 28 92 3.5 1 .8 62 92 85 30 91 3.2 1 .8 85 85 92 32 100 2.8 1 .8 100 92 92 34 92 2.71.5 85 85 85 36 100 2.6 1 .4 85 92 92 38 78 2.3 1 .4 88 100 100 40 75 2.3 1 .5 67 100 66 We conclude that, l ik.e previously reported cross-sectional studies, antenatal survei llance is highly gestational age dependent, and in fetuses less than 26 wks associated with a high false non-reassuring rate.

501 WHAT IS THE INTERVENTION RATE IN PATIENTS IN ANTEPARTUM TESTING FOR A PRIOR STILLBORN? Dena Towner MD" Richard Paul MD University of Southern California Los Angeles, California

In the era prior to antepartum evaluation and intervention for fetal indications, the Collaborative Perinatal Study published in 1972 that the perinatal mortality was 73 per 1000 in the pregnancy subsequent to a stillbom(SB). In contrast, our current institutional SB rate in women undergoing antepartum testing is 2/1000. The women at greatest risk of repeat SB are those with another known risk factor; ie, hypertension, diabetes and current IUGR. However this leaves a significant population with no other known risk factors. The purpose of this study is to detennine if a significant number of antepartum tests (APT) led to intervention in patients with a prior S8 and no other indication for testing, compared to patients with other indications for APT. From 1187 through 4/91 there were 355 patients tested that had a prior SB with no additional risk factors. Of these, 299 delivered prior to 41 weeks and 56 had gestations that exceeded 41 weeks. Onset of testing ranged from 28 wks to 42 wks, with a median of 35 wks. The earliest intervention occurred at 35 weeks, with the majority occurring after 37 completed weeks(39/42). The comparison group was 979 consecutive patients being tested for postdates(PD), diabetes(DM), IUGR, HTN or decreased fetal movement(DFM). Patients were tested once or twice weekly with NST & AFI or biophysical profile. Significant variable decelerations (FHR fall > 30 bpm & up to 15 sec or any fall lasting > 1 min), late decelerations, or AFI < 5cm led to further evaluation on L&D for delivery. Significantly less intervention occurred for ahnonnal testing in patients with prior SB delivering prior to 41 weeks 241299 (8%) than PD 118/497 (24%) p<O.OOOOI or DM 46/232 (20%) p<O.OOOI. Intervention rate was not different than DFM 6/121 (5%) p<0.37, HNT 4/19 (21 %) p <0.24, or IUGR 15/110 (13.6%) p<0.13. The intervention rate in patients with prior SB & PD 18/56 (32%) was not different than those with only PD 118/497 (24%) P <0.2. This data shows that patients with a prior SB as the only indication for APT have significantly less intervention than patients with DM or postdates, and an intervention rate similar to patients tested for JUGR, HTN and decreased fetal movement. Patients with a prior S8 whose gestation exceeds 41 weeks have a similar intervention rate as those patients whose only risk factor is postdates.

502

January 1992 Am J Obstet Gynecol

MEAN AMNIOTIC FLUID INDEX BY GESTATIONAL AGE IN DIABETIC AND NON·DIABETIC PREGNANCY. Montgomery OMx, Perlow JHx, Morgan MA, Nageotte MP. Garite TJ. Long Beach Memorial Womens Hospital. Long Beach, California University of California, Irvine Med. Center, Orange, California

The amniotic fluid index (AFI) has become an integral part of antenatal fetal assessment. However, presently there are no published data regarding the mean AFI at varying gestational ages in the pregnant diabetic. The objective of the study was to construct an AFI nomogram for the diabetic and non·diabetic populations at our institution. From 1/1/88·12131190, 249 diabetics (classes A·R) had a total of 1,506 AFI measurements at varying gestational ages. These values were compared with a control group consisting of 1,518 patients who had a total of 6.494 API measurements at corresponding gestational ages.

MEAN AFI BY GESTATIONAL AGE WITH 95% CONFIDENCE

15 INTERVALS

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Statistically significant increases in mean AFI were demonstrated at 32, 33. 36 and 37 weeks gestation between the diabetic and non· diabetic patients (p<.05), the maximum difference observed was 1.2 cm. These data provide the basis for future studies to validate the use of the AFI in the diabetic pregnancy.

503 HOW FREQUENTLY SHOUlDAFI'S BE REPEATED D.laqrew, R. Pircon, M. Nageotte, R.K. Freeman, W. Dorchester", Dept Ob/Gyn, long Beach Memorial Medical Center, long Beach, CA, Univ. of California, Irvine, Orange, CA.

The amniotic fluid index (AFI) has become a widely utilized technique for assessing fetal well·being. Intervals for measurement and cutoffs for intervention have been established by clinical experience. We analyzed AFl's on patients undergoing serial surveillance in order to evaluate once versus twice weekly measurements w~h respect to the chance of developing oligohydramnios (AFI < 5 cm) at each interval according to the in~ial AFI measurement. There were 11,759 AFl's of which 7,393 had a subsequent measurement w~hin 4 days and 8,094 in 7 days. In~ial

AFI's were compared w~h the subsequent lowest value at 4 and 7 day intervals. If the in~ial AFI was < 5.0 cm, 59.4% had persistence of this low level 4 days later. If the in~ial AFI was 5 to 8 cm. only 5.4% had subsequent measurements of < 5.0 cm 4 days later. AFI's < 5.0 cm 4 days after an initial AFI of 8 to 15 cm occurred only 0.6"10 of the time and only 0.4% if the in~ial measurement was 15 to 25 cm. A similar trend was noted at 7 day intervals. These results suggest the following: 1) an increased chance of developing oligohydramnios is present if an in~ial AFI is 8 cm or less. 2) Values above 8 cm are associated w~h a very low risk of oligohydramnios occurring in < 7 days and need not be repeated at < 7 day intervals.