Volume 168 Number I, Part 2

357 DILATION AND EVACUATION AFTER DETECTING FETAL ABNORMALITIES: A RELIABLE TECHNIQUE FOR CONFIRMING PRENATAL DIAGNOSES. Lp Shylman S Elias, JS DunganX , C Grevengood'<, SJ Grossx, PJ Kingx. University of Tennessee, Memphis. OBJECTIVE: We sought to determine whether abnormal prenatal diagnoses would be consistently confirmed in pregnancies terminated in !he second trimester by dilation and eV8wation (0 and E). STUDY DESIGN: The study population was deriYed from among WOOlen referred to our center between February 1987 and June 1992 and consisted of women determined to be carrying fetuses with genetic disorders or ultrasonographically.<Jetected malformations. The specific prenatal diagnosis, prognosis for the current pregnancy, potential for treatment prenatally or postnatally and risk of recurrence were reviewed with aU patients. In addition, pregnancy continuation or termination options were reviewed. AU patients who elected 10 terminate their pregnancies by labor induction techniques were referred to other centers, as we were unable to provide pregnancy termination for fetal indications by labor induction at our center. Pathologic and cytogenetic analyses were performed on all abortus specimens; other analyses (e.g., DNA, enzyme) were performed when indicated by the specific prenatal diagnosis. RESULTS: A total of 198 women elected 10 terminate their pregnancies after detection of fetal abnormalities; 93 women carrying fetuses with neural tube defects, 56 cases of fetal cytogenetic abnormalities, 33 cases of multiple congenital anomalies and 16 cases of fetal Mendelian disorders. Six women elected 10 undergo pregnancy termination by labor induction and were relerred to olher institutions. Mean gestational age of Ihe 192 women electing 0 and E was 17.9 weeks (range 14 - 22 weeks). In all but one case, prenatal diagnosis was confirmed by pathologic, cytogenetiC or DNA studies of the products of conception. In the one case, bacterial overgrowth precluded confirmation of fetal trisomy 18; however, fetal structural defects prenatally detected by ultrasonography (i.e., bilateral clubfeet, endocardial cushion defect, characteristic trisomy 18 hand positioning) were confirmed in the abortus specimen. CONCLUSIONS: 0 and E performed by experienced obstetrician­gynecologists is reliable for confirming most prenatal diagnoses and should be oHered to women who elect to terminate pregnancies in !he second trimester because of fetal abnormalities.

358 THE RISK OF SECOND TRIMESTER AMNIOCENTESIS IN TWIN GESTATIONS. A GbjdjnjX, L. lynch, C. Hicksx, G .

Berkowitzx, C.J. lockwood. MI.Sinai School of Medicine, NY,NY. OBJECTIVE: There are no case..:ontrol studies in the literature assessing the risks of genetic amniocentesis in uncomplicated twin pregnancies. We retrospectively compared pregnancy outcomes in 102 consecutive patients with twin pregnancies undergoing amniocentesis for fetal karyotype with 109 twin pregnancies undergoing routine sonographic studies at similar gestational ages. STUDY DESIGN: All spontaneous and induced twin gestations that underwent an ultrasound examination between 14 and 20 weeks were compiled for the period of Jan. 1987 to Jan. 1992. Excluded were patients having undergone mult~etal reductions or chorionic villous samplings and those with fetal anatomic or chromosomal anomalies, discordant growth (>20%) at the time of initial ultrasound, death or a monoamniotic sac detected at ultrasound. Follow-up was available in 95% of cases and 96% of controls. RESULTS: Amniocenteses were successful in 99.5% of cases. The mean maternal age was sign~icant/y higher among cases than controls [35.2 (±3.5) vs. 30.4 (±5.3) years; p < 0.0001]. No differences were noted between cases and controls for mean graVidity, parity, number of prior spontaneous losses and gestational age at uttrasound. Among the 204 case fetuses there were a total of 7 losses (3.4%): both twins at 22, 23 and 25 weeks, and one twin at 36 weeks. No losses occurred within 3 weeks of amniocentesis. Among the 218 control fetuses there were also 7 losses (3.2%): both twins at 18, 20 and 26 weeks, and one at 32 weeks. The relative risk of amniocentesis was 1.1 (95% confidence intervals: 0.4; 3.0). No differences were noted between cases and controls for gestational age at delivery, birth weight, mean Apgar scores at 1 and 5 minutes, length of neonatal stay and occurrence of respiratory distress syndrome. CONCLUSION: Second trimester amniocentesis in twin pregnancies appears to be a safe procedure.

SPO Abstracts 397

359 KSDUCBD PAIRING OF a-SA%BLLITB REGIONS IN BUNAR PBMALB MBIOSIS. BY Cheng, SM Gartler. Departments of OB/GYN and Medical Genetics, University of Washington, Seattle, WA. OBJBcrIV., To evaluate the role of centromeric a-satellite DNA repeats in chromosome pairing during meiosis. STUDY DBSIONI Using probes for the X chromosome a-satellite repeat and unique sequences obtained from an X chromosome library, the fluorescence hybridization pairing patterns of centric heterochromatin and euchromatic (unique) sequences in the X chromosomes of fetal oocytes were compared. RBSULTBI Of 31 zygotene cells displaying hybridization with the x chromosome library, 7 cells had 2 unpaired signals (23\), 14 cells had partially paired signals (45%), and pairing appeared complete in 9 cells (29%). In contrast, the a-satellite repeats were unpaired in 46 of 64 zygotenes (72\). Of 149 pachytenes with hybridization signals for the unique sequences, pairing was complete in 147 cells (>98\) and partial in 2 cells «2\), whereas 85 of 153 (56\) pachytenes were unpaired for the a-satellite repeat. An a-satellite probe for chromosome 18 demonstrated similar results, with 33 of 131 (26\) pachytenes unpaired at this region. CONCLUSION I These data suggest that highly repeated a-satellite sequences are not involved in meiotic pairing. possibly, these sequences are excluded from pairing in order to lower the frequency of unequal recombination.

360 TISSUE SPECIFIC MJSAICISM AM)NG FETUSES WITH PRENATALLY DIAGl'USED DIAPHRAGMATIC HERNIA. A. Donnenfeld, J. Bell, R. Librizzi, M. Nazir,-Y. Byers, A. Ludomirsky, S. weiner. MFM Sect. Dept. Ob/Gyn, Pennsylvania Hospital, Phila., PA. OBJECTIVE: 'lb determine if cytogenetic discrep­ancies between fetal blood and amniotic fluid are present in fetuses with prenatally diagnos­ed diaphragmatic hernia (D-hernia). STUDY DESIGN: 14 fetuses with prenatally diag­nosed D-hernia were studied by both amniotic fluid and fetal blood chromosome analysis. RESULTS: In one fetus with a normal karyotype on fetal blood, amniotic fluid mosaicism for a supernumerary isochromosome 12p (iso12p) was identified. Concordant aneuploidy in both fetal blood and amniocytes was found in 5 of the re­maining 13 fetuses (38%) (3 with trisomy 18, 1 with mosaic supernumerary iso12p in both fetal blood and amniocytes, 1 with an unbalanced translocation, and 8 with normal karyotypes). CONCLUSIONS: Since D-hernia is a common compon­ent of mosaic supernumerary iso12p syndrome and this chromosome abnormality is predominantly found in fibroblasts but not lymphocytes, an amniocentesis may be more accurate than fetal blood sampling in defining the true fetal chromosome status when diaphragmatic hernia is prenatally diagnosed.