Prevalence and risk factors of monochorionic diamniotic twinning after assisted reproduction: A six-year experience base on a large cohort of pregnancies.

Objective: To characterize the incidence and risk factors for monochorionic diamniotic(MC-DA) twinning after assisted reproductive technologies (ART).

Design: Retrospective population-based study.

Setting: The study was conducted in China; Department of Reproductive Medicine Center at The First Affiliated Hospital of Anhui Medical University.

Population: A cohort of 8860 clinical pregnancies after embryo transfer (ET) carried out in our center between 2011 and 2016 were retrospectively analyzed for the incidence of MC-DA twinning.

Methods: Logistic regression was used to model the effect on the incidence of MC-DA twinning after ART. Different clinical data (maternal age) and laboratory procedures (type of ET (fresh versus frozen), insemination (IVF or ICSI)), embryo stage at time of ET (cleavage or blastocyst)) on the incidence of MC-DA twinning were evaluated.

Main Outcome Measures: Monochorionic-diamniotic pregnancies were identified when more than one fetal poles was visualized in one gestational sac via trans-vaginal ultrasound at early first-trimester (7 to 8 weeks).

Results: The overall MC-DA twinning rate was 2.55% (226/8860). Eighty one MC-DA twinnings occurred in the fresh cycles and 145 in the frozen cycles (2.67% vs. 2.49%). MC-DA twinning incidence showed no significant difference whether ICSI was performed or not (2.79% vs. 2.44%). The MZT that resulted from single embryo transfer (SET) cycles (1.99%) was slightly lower than multiple embryo transfer cycles (2.61%),but with non-significance. However, women <35 years displayed a significant higher rate (2.81%) than women ≥35 years old (1.16%). Blastocyst transfer was associated with a significantly increase in MC-DA twinning incidence than cleavage-stage embryos transfer (2.79% VS 2.02%, P = 0.008). In the results of logistic regression analysis, blastocyst transfer is a major risk factor of MZT in the fresh cycles (P = 0.044), while maternal age plays a more important role in the frozen cycles (P = 0.004).

Conclusions: There is an elevated prevalence of MC-DA twinning after ART. Both maternal age and blastocyst transfer are risk factors of monozygotic pregnancy independently. Blastocyst transfer is a major risk factor of MC-DA twinning in the fresh cycles, while maternal age plays a more important role in the frozen cycles.