O-213 Analysis of risk factors for monozygotic twins following in vitro fertilization-embryo transfer
Authors: Gao M , Gao Y , Lu Q , Zhang X 
Published: July 2024

Abstract

Study question
To investigate the risk factors associated with the incidence of monozygotic twinning（MZT）following in vitro fertilization and embryo transfer (IVF-ET).

Summary answer
MZT following IVF-ET may be associated with a reduced endometrial thickness on the day of embryo transfer and a decrease in estradiol levels post-transfer.

What is known already
MZT pregnancy arises from the division of a single fertilized ovum, resulting in offspring with identical genetic material. These twins exhibit markedly higher rates of complications compared to dizygotic counterparts, including increased incidences of miscarriage, congenital anomalies, intrauterine fetal demise, growth restriction, and preterm delivery. The underlying biological processes leading to MZT remain elusive. Presently, scholarly discourse centers around two predominant models and one hypothesis: the zygote division model, the embryonic membrane fusion model, and the over-mature gametes hypothesis, respectively. IVF-ET has been implicated in the heightened occurrence of MZT, suggesting a potential iatrogenic element to this phenomenon.

Study design, size, duration
A retrospective cohort study has been conducted. We analyzed 582 IVF-ET cycles at a large teaching hospital from January 2007 to December 2022, including 291 clinically confirmed MZTs, and 291 matched non-MZTs.

Participants/materials, setting, methods
A total of 582 participants, 291 in both MZT group and non-MZT group. There were 146 fresh embryo transfer cycles and 145 frozen-thawed cycles in the MZT group. Each cycle type was matched on a 1:1 basis by age and embryo transfer date with a control group that did not result in MZT following IVF-ET. We examined the disparities between the MZT group and the non-MZT group, and performed the Logistics regression analysis.

Main results and the role of chance
Significant differences were observed in the MZT group compared to the non-MZT group in the fresh embryo transfer cycle, particularly regarding estradiol (E2) and progesterone (P) levels on day 7 post-transfer, E2/P ratios on day 14 post-transfer, and endometrial thickness on the day of transfer (p&lt;0.05). Logistic regression analysis indicated a correlation between reduced endometrial thickness on the transfer day and the occurrence of MZT. During the frozen-thawed cycle, significant differences were noted in E2/P ratios, E2 levels on day 7 post-transfer, and endometrial thickness on embryo transfer day (p&lt;0.05). Logistic regression analysis suggested that lower E2 levels on day 7 post-transfer and reduced endometrial thickness on embryo transfer day were predictive of MZT. Additional potential influencing factors included the duration of the participants’ menstrual cycle, the protocol of ovulation induction, and the duration of embryo culture in vitro.

Limitations, reasons for caution
Primarily, the retrospective design may introduce bias, notably due to the potential absence of comprehensive data. Secondly, the study is constrained by the sample size, with 146 fresh cycles and 145 frozen cycles, which may not provide a fully representative statistical power.

Wider implications of the findings
The incidence of MZT may implicate signaling pathways at the maternal-fetal interface, with early embryonic split potentially serving as a compensatory mechanism in response to suboptimal estrogen levels or diminished endometrial thickness, thus enhancing embryonic viability.

Trial registration number
not applicable