TWIN PREGNANCIES IN THE 2ND TRIMESTER IN WOMEN IN AN ALPHA-FETOPROTEIN SCREENING-PROGRAM - SONOGRAPHIC EVALUATION AND OUTCOME

OBJECTIVE. We correlated sonographic findings with fetal outcomes in w omen with unsuspected twin pregnancies who had sonography in the secon d trimester as part of a screening program for maternal serum alpha-fe toprotein (MSAFP) level and history of neural tube defect. MATERIALS A ND METHODS. The study group consisted of 97 women with twin pregnancie s who participated in a screening program for MSAFP level and history of neural tube defect. Seventy-three had normal MSAFP levels, 21 had e levated MSAFP levels, and two had low MSAFP levels. One patient had a family history of anencephaly. All 97 patients had sonography during t heir second trimester of pregnancy. Sonographic findings were reviewed retrospectively for information on gestational age, fetal anomalies, sex of the fetus, location of the placenta, presence and thickness of a dividing membrane, and interpretation of amnionicity and chorionicit y. Information on fetal outcome included gestational age at delivery, survival, birth weight, sex, congenital anomalies, obstetric complicat ions, amnionicity, chorionicity, and placental abnormalities. RESULTS. Amnionicity and chorionicity were correctly detected on sonograms in 44 (90%) of 49 diamniotic-dichorionic gestations, 23 (72%) of 32 diamn iotic-monochorionic gestations, and two (50%) of four monoamniotic-mon ochorionic gestations. Fetal anomalies were present at delivery in fiv e neonates and had been correctly detected at sonography in one (hemiv ertebra); one fetus with duodenal atresia had abnormal sonographic fin dings in the third trimester. Missed anomalies included absent forearm , cleft lip and palate, and imperforate anus. Sex of the fetuses was c orrectly predicted on the basis of sonographic findings in 40 of 43 pa irs. Nine twin pairs had possible twin-twin transfusion syndrome suspe cted sonographically on the basis of abnormal fluid volumes, discrepan t growth measurements, and abnormal findings on Doppler studies. Outco mes included two confirmed cases of the syndrome (two survivors, two d eaths) and three probable cases (six deaths); four pregnancies resulte d in eight survivors who were delivered after 34.4 weeks' gestation an d had birth weights in the 25th percentile or higher. Survival rates f or diamniotic-dichorionic, diamniotic-monochorionic, and monoamniotic- monochorionic gestations were 90%, 91%, and 50%, respectively. Fetuses in women with MSAFP levels greater than 4.5 multiples of the median a nd with monochorionic placentation had lower survival rates than fetus es in women with normal MSAFP levels and monochorionic placentation (6 7% vs 96%). Half the fetuses delivered after 20 weeks' gestation had b irth-weight discordance of less than 10%. Premature deliveries occurre d in 56% of pregnancies. CONCLUSION. The results suggest that (1) sono graphy is useful in predicting placentation, (2) placentation may be h elpful in predicting fetal outcome, (3) increased MSAFP levels correla te with increased perinatal mortality in diamniotic-monochorionic preg nancies, and (4) caution should be taken in diagnosing and determining prognosis for suspected twin-twin transfusion syndrome in the second trimester.