O-6: The Risk of Cytogenetic Abnormalities in the Late First Trimester in Multiple Gestation Pregnancies

Abstract

Objective: Multiple gestation pregnancies are a common result with In Vitro Fertilization (IVF). Previous studies have suggested an increased incidence of aneuploidy in twins. However, this elevated risk of cytogenetic abnormalities is not apparent amongst singleton pregnancies conceived via IVF. The objective of our study was to determine if there an increased risk of chromosomal abnormalities in IVF pregnancies of high-order multiple gestation, compared to singleton pregnancies. Design: Retrospective case control study. Materials and Methods: All IVF pregnancies that presented to our institution for Chorionic Villus Sampling (CVS) between 1999–2004 were evaluated. All procedures were performed on ultrasound documented viable gestations between 9 and 12 weeks. Pregnancies were evaluated based on order of multiple gestation: singleton, twins or triplets. Women under the age of 35 were excluded. Monozygotic twin gestations were excluded. Cytogenetic analysis was compared between the 3 groups. Data was analyzed using the Chi-square test. Results: A total of 443 patients undergoing prenatal diagnosis secondary to advanced maternal age were studied. The mean age of patients was 40.2 years in the singleton group, 39.1 years in the twins group and 38.2 years in the triplets group. 200 fetuses in the singleton group, 191 fetuses in the twins group and 294 fetuses in the triplets group were sampled. The singleton group contained 16/200 (8.0%) fetuses with chromosomal abnormalities, compared to 14/191 (7.3%) in the twins group and 14/294 (4.8%) in the triplets group (p=ns). Overall, in the 200 singleton pregnancies, 101 sets of twins and 103 sets of triplets sampled, we found 16/200 (8.0%) chromosomal abnormalities in the singleton group, 14/101 (13.9%) in the twin group, and 10/103 (9.7%) in the triplet group (p=ns). Conclusion: Our study demonstrates that fetuses conceived in high-order multiple gestations are not prone to a greater incidence of cytogenetic abnormalities compared to singleton pregnancies conceived with IVF. Although multiple gestation pregnancies may be associated with higher perinatal morbidity, it appears that these fetuses do not face an elevated risk of chromosomal abnormalities.