Fresh versus frozen embryo transfer for full-term singleton birth: a retrospective cohort study

Abstract

BackgroundImprovements in vitrification and frozen embryo transfer (FET) technologies have rapidly increased, and some evidence suggests that FET may increase pregnancy rates and lead to more favourable perinatal outcomes. However, the outcome of interest should be offspring safety. Therefore, the primary objective of our study was to investigate whether FET was preferable to fresh embryo transfer (ET) in terms of full-term neonatal birthweight and congenital malformations.MethodsThis was a retrospective cohort study of patients with no pregnancy-related complications who underwent first fresh ETs (n = 2059) or FETs (n = 2053), resulting in full-term singletons births. Outcome measures were neonatal birthweight, low birthweight (LBW), small-for-gestational age (SGA), large-for-gestational age (LGA), macrosomia and congenital malformations. Additionally, we used logistic regression to adjust for baseline characteristics (age, BMI, No. of embryos transferred and embryo stage) between the two groups.ResultsThe mean neonatal birthweight was higher for singletons born after FET than for singletons born after fresh ET (3468.7 ± 475.3 vs. 3386.7 ± 448.1; p < 0.001). The frequencies of full-term singleton LBW and SGA after FET were significantly lower than those after fresh ET (1.7% vs. 3.0 and 4.4% vs. 6.7%, respectively), with adjusted rate ratios of 0.59 (95% CI, 0.37 to 0.98; p = 0.026) and 0.73 (95% CI, 0.55 to 0.99; p = 0.041), respectively. FET resulted in higher frequencies of macrosomia and LGA (15.1% vs 10.2 and 22.8% vs. 17.5%, respectively) than fresh ET, with adjusted rate ratios of 1.43 (95% CI, 1.16 to 1.75; p = 0.001) and 1.26 (95% CI, 1.07 to 1.49; p = 0.007), respectively. Furthermore, the incidence of congenital malformations was not different between the two groups (1.2% vs. 0.9%), with a rate ratio of 0.288.ConclusionsAfter the cycles with pregnancy-related complications were excluded and after adjustments for baseline characteristics, women undergoing FET were associated with a higher neonatal birthweight than women undergoing fresh ET cycles. Additionally, the FET protocol was associated with lower rates of LBW and SGA and higher rates of macrosomia and LGA than the fresh ET protocol. Meanwhile, no difference in the congenital malformation rate was evident between the two groups.

The Difference in Birthweight in Singletons Born After Fresh Embryo Transfer and After Frozen Embryo Transfer Becomes Significant in the Late Third Trimester

“…Our ndings are consistent with the pre-existing meta-analysis [3,29] and retrospective studies [30,31] published until 2018 showing that singletons born after FET have higher birth weight and higher gestational age at birth but a higher risk of hypertensive disorders of pregnancy, while singletons born after fresh ET tend to have a higher risk of preterm birth and low birthweight. However, our single-center singleton study showed that compared to those born after fresh ET, singletons born after FET had higher birth weight but not increased LGA.…”

Large-for-gestational age is male-gender dependent in artificial frozen embryo transfers cycles: a cohort study of 1295 singleton live births

“…placenta previa, placental abruption, preterm delivery, low birth weight, perinatal mortality and SGA. Moreover, previously published studies have also reported that infant birth weights from FET cycles were higher than those of fresh embryo transfer cycles, with a crude mean difference of 126 g (65-205 g) calculated from their reports (Ishihara et al, 2014;Li et al, 2014;Pinborg et al, 2014;Ozgur et al, 2015;Korosec et al, 2016;Luke et al, 2017;Spijkers et al, 2017;Tsuji et al, 2017;Vidal et al, 2017;Zhang et al, 2018;Wei et al, 2019). In studies defining LGA according to the 90th percentile birth weight of a reference population, the LGA rates reported from FET cycles ranged between 13 and 23% (Korosec et al, 2016;Luke et al, 2017;Zhang et al, 2018;Wei et al, 2019).…”

Is Embryo Cryopreservation Causing Macrosomia—and What Else?

“…Several studies suggested that children born following FET have similar or in most areas even better perinatal outcome, as compared to children born after fresh ET (23,24). Moreover, while FET was shown to be associated with lower risk of prematurity and LBW in singletons, when compared with fresh ET, there is a growing concern that children born after FET have increased risk of LGA and/or macrosomia (25). Macrosomic/LGA births have a higher risk of fetal hypoxia, stillbirth, shoulder dystocia, cesarean section, postpartum hemorrhage, perineal lacerations and neonatal metabolic disorders at birth (26).…”