177 FIRST-TRIMESTER SCREENING FOR TRISOMY 21 IN PREGNANCIESCONCEIVED BY IN VITRO FERTILIZATION SRIRAM C. PERNI1, ROBINB. KALISH1, GEETA SHARMA1, MERUKA GUPTA1, JENNIFER E. CHO1,STEPHEN T. CHASEN1, 1Weill Medical College of Cornell University,Obstetrics & Gynecology, New York, NY

OBJECTIVE: The aim of our study was to examine the effect of in vitrofertilization (IVF) on first-trimester levels of pregnancy-associated plasmaprotein A (PAPP-A), free beta-human chorionic gonadotrophin (b-hCG), andnuchal translucency (NT) measurements used in aneuploidy screening.

STUDY DESIGN: We compared the first-trimester maternal dried wholeblood specimens for PAPP-A and b-hCG of 31 singleton pregnancies conceivedby IVF with 135 pregnancies conceived spontaneously. Maternal serumbiochemistry analysis was performed by NTD Laboratories and was reportedas multiples of the median (MoM). NT was measured using the Fetal MedicineFoundation protocol from 11-14 weeks of gestation. Pregnancies conceived byIVF were matched with four spontaneous conception controls. Subgroups werestratified based on gestational age. Free b-hCG, PAPP-A, and NT levels werecompared between the IVF and control groups using the Mann-Whitney Ustatistical test. A P value < 0.05 was considered statistically significant.

RESULTS: PAPP-A levels were 6.6% lower and free b-hCG levels were 2.8%higher in pregnancies conceived by IVF compared to spontaneous conceptions,although this did not reach statistical significance. Among the patientspresenting at the earliest gestational age range, median PAPP-A was significantlylower (0.82 MoM versus 1.68 MoM, P = 0.036) in the IVF pregnancies. b-hCGand NTmeasurements did not differ significantly between the two groups at anygestational age. However, there was a trend towards increased median NTmeasurements in IVF pregnancies from 11.5 - 12.5 weeks of gestation (1.55 mmversus 1.45 mm, P = 0.09) compared to the controls at the same gestational age.

CONCLUSION: In singleton pregnancies conceived by IVF, PAPP-A levelsappear to be lower early in gestation. Larger studies are necessary to explore thepossibility of using appropriate adjustment factors to correct for IVF gestations.

178 VARIATION IN THE DECISION TO TERMINATE PREGNANCY IN THESETTING OF FETAL ANEUPLOIDY BRIAN L. SHAFFER1, AARON B.CAUGHEY1, MARY E. NORTON1, 1University of California, San Francisco,Obstetrics, Gynecology and Repro. Sciences, San Francisco, CA

OBJECTIVES: To investigate the rate of pregnancy terminations of variousfetal aneuploidies and to evaluate predictors of this choice.

STUDY DESIGN: A retrospective cohort study identified all patients withany of six common fetal aneuploidies (trisomies 21, 18, and 13; 45,X; 47,XXY;and 47,XYY) at a referral prenatal diagnosis unit from 1984-2003. We abstractedmaternal ethnicity and age as predictors of the decision to terminate. Statisticalcomparisons were made using the chi-square test.

RESULTS: Overall, we diagnosed 803 fetuses with aneuploidy. The overallrate of termination was 82%. However, the rate of termination variedsignificantly both by type of aneuploidy (P < 0.001) and ethnicity (see Table).

CONCLUSION: In our population of patients there was a high terminationrate for lethal and severe karyotypes, which was less pronounced with improvedprognosis. Understanding factors surrounding patients’ decisions to terminateis important for both counseling and establishing population-based screeningstrategies.

179 HOW TO COMBINE FIRST- AND SECOND-TRIMESTER DOWNSYNDROME SCREENING TESTS PETER BENN1, JAMES EGAN2, 1Univer-sity of Connecticut, Pediatrics, Farmington, CT 2University of Connecticut,Obstetrics/Gynecology, Farmington, CT

OBJECTIVE: To illustrate that Down syndrome risk assessments using first-and second-trimester tests should not be combined unless correlation factorsbetween the tests are incorporated into the risk calculation.

STUDY DESIGN: Likelihood ratios (LRs) are the numeric factors used tomodify a woman’s age-specific risk for an affected pregnancy. LRs werecalculated for various combinations of nuchal translucency (NT) and serumscreening tests (PAPPA, fbhCG, AFP, hCG, uE3, and INH-A). LRs werecomputed for a typical Down syndrome–affected pregnancy (with results equalto the affected pregnancy median MoM for each test) and a typical normalpregnancy (with results equal to 1.0MoM for each test). Calculations were basedon statistical parameters from the SURUSS study (Wald et al, 2003;www.ncchta.org).

RESULTS: As can be seen from the data in the Table, LRs for combinationsof tests are not equal to the product of LRs for the component tests. Forexample, for the affected pregnancy receiving all 7 tests, the correct LR (260.9)is not equal to the net LR that would be applied if the first-trimester tests (NT,PAPP-A, and fbhCG) and the second-trimester tests (AFP, hCG, uE3, and INH-A)were viewed as being independent (36.1314.0 = 505.4).

CONCLUSION: Combinations of tests provide powerful screeningprotocols with potentially very high, or very low, LRs. However, correct estimatesof risk require the use of the appropriate LRs, which must incorporate allcorrelations between the first- and second-trimester tests.

180

Termination rates for various aneuploidies

T21(n = 458)

T13 & T18(n = 222)

45,X(n = 52)

47, XXY(n = 42)

47, XYY(n = 25)

All P< 0.001 87% 83% 65% 70% 40%White 90% 86% 70% 76% 36%Afr. Am. 91% 100% * * *Asian 87% 89% 66% 50% *Hispanic 70% 75% 61% 71% 100%Filipino 80% 57% 66% 0% (0/1) *P value 0.006 0.201 0.945 0.259 0.320

LRs for various combinations of tests with correlations included

Down syndrome Unaffected

No test 1.0 1.00NT alone 4.9 0.28PAPP-A, fbhCG 10.6 0.15NT, PAPP-A, fbhCG 36.1 0.08AFP, uE3, hCG (triple test) 8.4 0.13AFP, uE3, hCG, INH-A (quad test) 14.0 0.08All 7 tests 260.9 0.02

December 2003Am J Obstet Gynecol

S112 SMFM Abstracts

FAILURE TO DIAGNOSE SPINA BIFIDA BY MATERNAL SERUM ALPHA-FETOPROTEIN SCREENING DAVID WALTON1, CAROL NOREM2, ED-GAR SCHOEN2, JENNIFER O’KEEFE2, ROBYN KRIEGER2, TRINH TO2,1The Permanente Medical Group, Obstetrics and Gynecology, Oakland, CA2The Permanente Medical Group, Genetics, Oakland, CA

OBJECTIVE: Despite advances in prevention, neural tube defects continueto affect 1 in 1200 pregnancies in Northern California. This abstract reports theresults of the Kaiser Permanente Northern California screening program forneural tube defects, with specific focus on spina bifida.

STUDY DESIGN: This was a retrospective study using outcomes from theperiod August 1995 through July 2001. The data were derived from electronicdatabases maintained by Kaiser Permanente, including information from theState of California Expanded Alpha-Fetoprotein Program. In addition, second-trimester ultrasound examination was standard for all pregnant womenreceiving care at Kaiser Permanente. Maternal serum screening and ultrasoundwere performed according to accepted standards.

RESULTS: 145,100 women (74% of 195,000 pregnant women) participatedin the serum screening program during this period. 160 neural tube defects(prevalence 1:1219) occurred; 85 had anencephaly; 59, spina bifida; and 16,encephalocele. Of the 59 cases of spina bifida, 52 were isolated, 5 weresyndromic, and 2 were closed lesions. 55 (93%) were detected antenatally and 4(7%) were detected postnatally. The 4 postnatal cases included the 2 closedlesions (negative serum screening/normal ultrasound), and 2 open lesions (onewith negative serum screening/no ultrasound, one with no serum screening/normal third-trimester ultrasound). From the 57 cases of open spina bifida, 36had serum screening and 21 had ultrasound alone. 13 of the 36 serum-screenedspina bifida pregnancies (36%) were screen negative.

CONCLUSION: Serum screening performs poorly in the detection of spinabifida; 36% of the cases would have been missed with serum screening alone.Patients who had ultrasound accompanied by serum screening or ultrasoundalone had a 98% detection rate of open spina bifida. Routine second-trimesterultrasound is necessary to attain an acceptable detection rate of open spinabifida.