400 SPO Abstracts

369 COOK OB/GYN CATHETER MULTICENTER CHORIONIC VILLUS SAMPLING TRIAL: COMPARISON OF BIRTH DEFECTS WITH EXPECTED RATES. K. Blakemore. K. Filkins, D. Luthy, J. Priest", l. Platt, A. Medearis, M. Verp, l. Padilla, S. Warsof, A. ScommegnaX

, P. WestonX

OBJECTIVE: The null hypothesis is that offspring of women undergoing first trimester chorionic villus sampling (CVS) for prenatal diagnosis do not experience an increased rate of birth defects versus those not subjected to CVS. STUDY DESIGN: Follow-up information on the presence or absence of major malformations was obtained on 3,904 offspring of women who had first trimester CVS using the Cook Ob/Gyn catheter. The incidence of all major malformations and specific malformations was compared with data from the Collaborative Perinatal Project, Heinonen, et al. 1977, as well as other registries. RESULTS: A total of 79 offspring with major malformations were identified (2.02%). Compared to background rates, there was no increase in the incidence of total malformations, or specific malformations in the subjects. One institution experienced three limb reduction defects in their series (Burton B. et al. Obstet.Gynecol. 79:726, 1992) but no other institution in the multicenter trial experienced any limb reduction defects and the overall rate was the expected background rate. CONCLUSION: CVS was not found to result in an increase in major birth defects, or in specific categories of birth defects in this series. Since first trimester ultrasonography in conjunction with CVS cannot identify a number of significant malformations, follow-up second trimester ultrasonography is offered to patients seeking prenatal diagnosis by CVS.

370 Withdrawn due to presentation

January 1993 Am J Obstet Gynecol

371 NATURAL OBSTETRICAL HISTORY OF TRISOMY 18. D.N. Saller. Jr .. C.E. Oyerx, J. Star. JA Canlckx Brown Unlverslty/Women & Infants Hosp .. Providence. RI OBJECTIVE: To detennine whether the obstetrical course of trisomy 18 pregnancies Is different from that of euploid pregnancies. STUDY DESIGN: Forty-nine trisomy 18 pregnancies were Identified by the cytogenetics laboratory at a single institution between 1980 and 1992. Clinical and laboratory records of all 49 were reviewed. Eight had fetal demise and 19 had pregnancy termination. Of the 22 liveborns. 2 were prenatally diagnosed. 9 (41%) were delivered before 37 weeks. RESULTS: Of 22 liveborns. 15 (68%, 95% CI: 45-86%) were delivered by cesarean section for Indications of fetal distress (n=12). deep vartables of the upper twin (n=l). arrest of labor (n=l), and scheduled repeat (n=l). The overall cesarean section rate for the hospital ranged from 19.1-22.6%. Of the 7 vaginal dellvertes. 2 refused cesarean section. Of 5 patients with LIS ratios at 35 - 38 weeks. all were :S;1.8. Each was lower than 10 matched controls (Matched rank sum test p<O.OOl). Since 1990 and the availability of maternal serum screening for trisomy 18 (Canlck et aI, Prenat Diagn,1O;546,1990). 6 of 15 cases of trtsomy 18 were liveborn (3 by cesarean section). None of these six pregnancies had maternal serum screening. CONCLUSIONS: These data confirm that undiagnosed trisomy 18 pregnanCies are associated with an Increased CIS rate. first suggested by Schneider et al (AlOG 140:367,1981). The Immature LIS may be related to adrenal hypoplasia associated with trisomy 18. In the absence of prenatal diagnosis. attempts to manage growth retarded trisomy 18 pregnancies by delivery may be complicated by the confounding immature LIS ratio. These data reinforce the importance of (1) karyotype In the evaluation oflUGR. and (2) prenatal diagnosis of trisomy 18. regardless of gestation.

372 SECOND TRIMESTER NUCHAL SKIN-FOLD THICKNESS IN NORMAL AND DOWN SYNDROME PREGNANCIES . ..&, Donnenfeld, D. Carlson, G. Palomaki. L. Platt. Pennsylvania Hospital, Phila, PA, Cedars-Sinai Medical Center, l.A., CA, Foundation for Blood Research, Scarborough, ME. OBJECTIVE: To determine if sonographic measurement of nUchal skin-fold thickness is a useful screening test for Down syndrome. STUDY DESIGN: Second trimester nuchal Skin-fold thickness measurements were prospectively determined in 1240 women undergoing amniocentesis for the indication of advanced matemal age. Measurements were obtained as described by Crane et al. (Ob Gyn 77: 533, 1991). R ESU L TS: There were 1225 chromosomally normal pregnancies and 12 fetuses with Down syndrome. Fifteen fetuses had measurements >6 mm and 1 of these had Down syndrome. The median nuchal skin-fold thickness measurement in Down syndrome pregnanCies was 3.2 mm (range 2.0-6.2) and for chromosomally normal pregnancies was 3.0 (range 1.0-8.2). By the Mann-Whitney rank-sum test there was no statistically significant difference in second trimester nuchal skin-fold thickness measurements between normal and Down syndrome fetuses (p=O.7). A statistically significant difference would have been detected if nuchal skin-fold measurements differed between Down syndrome and chromosomally normal fetuses by even 1 mm. Overall, excess nuchal skin-fold thickness as a screening test for Down syndrome identified 1 of 12 (8%) of affected pregnancies, had a positive predictive value of 1 :15 (6%) and a false positive rate of 15:1225(1.2%). CONCLUSIONS: Excess nuchal skin-fold thickness is a poor screening test for Down syndrome but, when present, may warrant amniocentesis.