‘Vanishing twin syndrome’ following frozen embryo transfer has no detrimental effects on offspring growth and development up to 3 years

CONTEXT: Vanishing twin syndrome (VTS) is a common condition in assisted reproductive procedures, where a multi-fetus pregnancy is spontaneously reduced to a singleton pregnancy. However, the effects of VTS on the development of the remaining fetus is relatively unknown. AIMS: The purpose of this study was to estimate the effect of VTS on the dynamic measurement of growth and development of the singletons (0-3 years) born from frozen embryo transfer (FET). METHODS: This study was a retrospective cohort design and was carried out from January 2017 to December 2023. To optimize statistical efficiency and reduce confounding variables, singletons conceived using VTS were matched at a 4:1 ratio based on the couples' ages, body mass index, occupation, women's anti-Müllerian hormone (AMH) levels, and embryo status. Ultimately, 66 children in the VTS group and 264 children in the non-VTS group were included in the final analysis. KEY RESULTS: After propensity matching, there was no significant difference in growth and development of children between the VTS group and the non-VTS group. The number of embryos transferred in the VTS group were higher than the non-VTS group (P < 0.0001). The height and the head circumference (at 3 months) in the VTS group were lower than the non-VTS group (P < 0.05). CONCLUSIONS: The occurrence of VTS did not detrimentally affect the growth and development of offspring (0-3 years) from FET. IMPLICATIONS: More comprehensive and long-term follow-up results are needed for further verification. More than one embryo transfer not only increases the rate of multiple births, but also increases the occurrence of VTS in assisted reproductive technologies (ART).