Blastocyst transfer is associated with an increased rate of monozygotic twins

Abstract

Embryo transfer of two blastocysts has been reported to reduce high-order multiple gestation rates while maintaining pregnancy rates. The purpose of this study was to evaluate the incidence and characteristics of multiple gestations associated with blastocyst transfer. All egg donation cycles and IVF cycles in women under age 35 years who had three or more 8-cell embryos on post-aspiration day 3 were eligible for blastocyst transfer. A total of 25 transfer cycles were thus achieved between 1/1/99 and 10/12/99. The control group consisted of patients whose cycles took place during calendar years 1997 and 1998. Similar protocols were used; however, all transfers were performed 72 hours after aspiration. All subjects underwent standard COH with leuprolide down-regulation followed by hMG or FSH stimulation. Embryos were cultured in 50 μL drops of media under oil, with P1 and blastocyst media used sequentially. Two blastocysts were transferred in 22 cases (88%), 3 in 2 cases, and 4 in one case. The clinical pregnancy rate was 18/25 (72%), the multiple gestation rate was 11/18 (61%), and the implantation (chorionic sac per embryo) rate was 30/54 (56%). Of the 18 clinical pregnancies, 7 (38.9%) were singletons and 8 (44.4%) were twins. There were 3 high-order multiple gestations, all associated with monozygotic twinning (3/18 [16.7%]; 95% CI 4–41%), a rate which is significantly higher than the established rate of 0.4% in the general population. Two of these had 2 blastocysts transferred, resulting in 2 sacs and 3 viable fetuses. The third patient had a known balanced chromosomal translocation and underwent transfer of 4 blastocysts, resulting in 3 chorionic sacs and 4 viable fetuses. There were 59 clinical pregnancies in the control group, with 7 high-order multiple gestations but only 1 monozygotic twin (1.7%; P<.05 vs. blastocyst transfer). We conclude that clinical blastocyst transfer 1) maintains good pregnancy rates in this group of patients and 2) is associated with a statistically significant increased rate of monozygotic twinning.