P-139 The incidence of monozygotic twins after the usage of calcium ionophore or after trophectoderm biopsy in ART treatment
Authors: Yong F.C.H 
Published: June 2022

Study question

To investigate whether the usage of calcium ionophore or trophectoderm biopsy affect the occurrence of monozygotic twins (MZT) in assisted reproductive treatment (ART) treatment.

Summary answer

Despite the increase was not statistically significant, higher percentage of MZT were observed in both group with calcium ionophore usage and trophectoderm biopsy.

What is known already

The incidence of monozygotic twins (MZT) in natural conception is approximately 0.4% worldwide but it is estimated that there is at least a 2-fold rise in the incidence of MZT after assisted reproductive technology compared with natural conception, although the reason is still under debate. The effectiveness of calcium ionophore in assisting oocytes activation and fertilisation has been widely studied. Most studies reported no impact upon embryo viability and reproductive potential after trophectoderm biopsy. However, the impact of calcium ionophore or trophectoderm biopsy on subsequent in vivo development of the blatocyst remains unclear.

Study design, size, duration

This is a retrospective observational cohort study of frozen embryos transfers (FET) that have achieved clinical pregnancy between January 2019 and October 2021. In this study, 709 FET cycles were included and analysed based on i) with or without calcium ionophore treatment after ICSI/IVF on oocytes retrieval day; ii) with or without trophectoderm biopsy on day 5 or 6. The results were analysed to identify possible risk factors affecting the prevalence of monozygotic twins.

Participants/materials, setting, methods

The cases with positive beta-hCG test were followed-up and analysed for the occurrence of MZT. The diagnosis of MZT was established by transvaginal ultrasound performed at 4-6 weeks after the transfer. The visualization of uteri containing more than one fetus, either in one sac (monochorionic monoamniotic) or in two sacs separated by a septum (monochorionic diamniotic) is suggestive of MZT. Data were analysed by Fisher’s exact test and Odd Ratio.

Main results and the role of chance

Data comprising a total of 709 FET cycles in a single clinical setting were analysed. Among 449 cases of clinical pregnancies, 8 cases of MZT occurred. A higher percentage of MZT (1.78%) after blastocyst transfer in ART treatment was observed as compared to natural conception (0.04%).

There was a higher incidence of MZT in trophectoderm biopsy group as compared with non-biopsy group (2.3% vs 1.45% respectively, odds ratio [OR]= 1.59, 95% CI 0.39–6.46). However, there was no statistically significant (P-value=0.556, CI = 95%).

The incidence of MZT following the calcium ionophore usage was higher compared with the group without calcium ionophore usage (2.33% versus 1.72%, OR = 1.36, 95% CI 0.16–11.3). There was no significantly higher risk of MZT with calcium ionophore versus non-calcium ionophore cycles (P-value= 0.493, CI = 95%).

Limitations, reasons for caution

The sample examined in this study is limited in size thus more studies are needed to achieve satisfactory statistical power. MZT diagnosed with ultrasound is difficult to differentiate from dichorionic monozygotic twins. The definitive diagnosis of monozygosity is only possible by DNA analysis of all the twins born.

Wider implications of the findings

These findings can draw attention to study the effect of calcium ionophore on embryo development and the mechanism behind MZT. Based on the findings, the patients undergoing ART treatment should be informed with the risk associated with higher incidence of MZT.

Trial registration number

NA