Incidence of monozygotic twinning with blastocyst transfer compared to cleavage stage transfer

Abstract

Objective: A higher incidence of monozygotic twinning (MZT) has been reported with IVF especially when the zona pellucida is breached. A few reports have suggested that blastocyst transfer(BT) may further predispose to MZT but information specifically comparing blastocyst to cleavage stage transfer, with respect to the incidence of MZT, is lacking. The present study addresses this issue in a large series of day 3 and day 5 embryo transfers(ET) performed during the same time period.Design: Retrospective study.Materials/Methods: All viable pregnancies conceived in our IVF program since January 1998 were analyzed. Embryos were cultured in P1 + 10%SSS (Irvine Scientific) until day 3 and moved to Blastocyst Medium + 10%SSS (Irvine Scientific) if extended culture was performed. Viable pregnancies were initially assessed by vaginal ultrasound at 7 weeks of gestation and the final outcome of each pregnancy was recorded. The incidence of MZT was examined for day 3 and day 5 transfers.Results: There were 11 incidences of MZT out of 197 viable pregnancies (5.6%) with BT compared to 7 out of 357 viable pregnancies (2%) with day 3 ET (p <0.03). Interestingly, in 10 out of 18 pregnancies, MZT was observed in the setting of a high-order multiple gestation (6/11 for BT and 3/7 for day 3-ET). In the day 3-ET group, assisted hatching and/or ICSI did not increase MZT (4/213 =1.9%) compared to cycles without zona breaching (3/144=2.1%). Similarly, in the BT group, ICSI did not increase the incidence of MZT (4/74 =5.5% for ICSI and 7/123=5.7% for non-ICSI IVF). In the BT group, the final outcome of the pregnancies showed spontaneous resolution of one of the MZ twins in 4/11 cases and one spontaneous loss of the entire pregnancy, while in 6/11 cases MZT persisted (one triplet pregnancy had multifetal reduction of the MZ twins). In the day 3-ET group, MZT persisted in all 7 pregnancies (4 had multifetal reduction).Conclusions: Compared to day 3-ET, BT seems to significantly increase the incidence of gestations with MZT. This information should be taken into account when counseling patients about the pros and cons of extended culture. The mechanism of MZT is likely to be multifactorial. It could be related to blastocyst hatching from a zona which has been hardened by prolonged culture, combined with altered polarity and decreased adhesiveness of the inner cell mass as well as increased apoptosis in media containing excessive glucose levels.Supported by: None Objective: A higher incidence of monozygotic twinning (MZT) has been reported with IVF especially when the zona pellucida is breached. A few reports have suggested that blastocyst transfer(BT) may further predispose to MZT but information specifically comparing blastocyst to cleavage stage transfer, with respect to the incidence of MZT, is lacking. The present study addresses this issue in a large series of day 3 and day 5 embryo transfers(ET) performed during the same time period. Design: Retrospective study. Materials/Methods: All viable pregnancies conceived in our IVF program since January 1998 were analyzed. Embryos were cultured in P1 + 10%SSS (Irvine Scientific) until day 3 and moved to Blastocyst Medium + 10%SSS (Irvine Scientific) if extended culture was performed. Viable pregnancies were initially assessed by vaginal ultrasound at 7 weeks of gestation and the final outcome of each pregnancy was recorded. The incidence of MZT was examined for day 3 and day 5 transfers. Results: There were 11 incidences of MZT out of 197 viable pregnancies (5.6%) with BT compared to 7 out of 357 viable pregnancies (2%) with day 3 ET (p <0.03). Interestingly, in 10 out of 18 pregnancies, MZT was observed in the setting of a high-order multiple gestation (6/11 for BT and 3/7 for day 3-ET). In the day 3-ET group, assisted hatching and/or ICSI did not increase MZT (4/213 =1.9%) compared to cycles without zona breaching (3/144=2.1%). Similarly, in the BT group, ICSI did not increase the incidence of MZT (4/74 =5.5% for ICSI and 7/123=5.7% for non-ICSI IVF). In the BT group, the final outcome of the pregnancies showed spontaneous resolution of one of the MZ twins in 4/11 cases and one spontaneous loss of the entire pregnancy, while in 6/11 cases MZT persisted (one triplet pregnancy had multifetal reduction of the MZ twins). In the day 3-ET group, MZT persisted in all 7 pregnancies (4 had multifetal reduction). Conclusions: Compared to day 3-ET, BT seems to significantly increase the incidence of gestations with MZT. This information should be taken into account when counseling patients about the pros and cons of extended culture. The mechanism of MZT is likely to be multifactorial. It could be related to blastocyst hatching from a zona which has been hardened by prolonged culture, combined with altered polarity and decreased adhesiveness of the inner cell mass as well as increased apoptosis in media containing excessive glucose levels. Supported by: None