Frozen–thawed embryo transfer (FET) has increased steadily worldwide over the past few years (De Geyter et al., 2020; Zegers-Hochschild et al., 2020). In 2015, FET accounted for about 40% of all IVF cycles in Europe (De Geyter et al., 2020). The freeze-all strategy has reported successful results with higher live birth rates and lower incidence of ovarian hyperstimulation syndrome compared with fresh embryo transfer (Roque et al., 2019; Wei et al., 2019). Some studies have suggested that singletons born after FET also have better neonatal outcomes compared with singletons born after fresh embryo transfer, e.g.