Outcome of twin gestations after first trimester chorionic villus sampling

Objective: To tabulate genetic results and obstetric outcomes of twin pregn ancies after first-trimester chorionic villus sampling (CVS). Methods: The study included 262 consecutive women with twin pregnancies who had first-trimester CVS between 1988 and 1998. Results: Major indications for prenatal diagnosis included maternal age (n = 82), pregnancies after intracytoplasmic sperm injection (n = 114), or bot h (n = 33). Among 524 fetuses, 519 were sampled adequately. Cytogenetic res ults were incorrect because of sampling the same fetus twice in two pregnan cies. In three pregnancies, contamination caused by mixed sampling made cyt ogenetic results uncertain. Correct genetic diagnoses were obtained in 509 fetuses, 24 of which had chromosomal abnormalities on direct preparations a nd four of which had monogenetic conditions. Additional invasive procedures were done on five occasions. Fifteen fetuses were terminated selectively. The total fetal loss rate was 5.5% (28 of 509). The indication for the proc edure did not significantly determine the fetal loss rate. The mean +/- sta ndard deviation (SD) gestational age at birth was 35.9 +/- 2.9 weeks, and t he mean +/- SD birth weights for twins A and B were 2429 +/- 589.1 g and 23 78 +/- 588.5 g, respectively. Conclusion: First-trimester CVS is an accurate means of prenatal genetic di agnosis in twins, offering early selective termination in cases of abnormal genetic results in one of the fetuses. (Obstet Gynecol 2000;96:714-20. (C) 2000 by The American College of Obstetricians and Gynecologists).