The impact of embryo quality on singleton birthweight in vitrified-thawed single blastocyst transfer cycles

Abstract

Study question: Does the quality of a single transferred blastocyst affect singleton birthweight in frozen-embryo transfer (FET) cycles?

Summary answer: The transfer of a poor-quality blastocyst was associated with lower mean birthweight and gestation-adjusted birthweight (Z-scores) when compared with the transfer of an excellent-quality blastocyst during FET cycles.

What is known already: Embryo quality is a strong predictor of IVF success rates. However, very few studies have examined the effect of embryo quality on singleton birthweight.

Study design, size, duration: This retrospective study involved singleton live births born to women undergoing frozen-thawed single blastocyst transfers during the period from January 2010 to December 2017 at a tertiary care centre.

Participants/materials, setting, methods: A total of 1207 women who fulfilled the inclusion criteria were included and were grouped into four groups depending on the blastocyst quality: excellent, good, average and poor. The primary outcome measure was singleton birthweight. The Z-score was employed to calculate the birthweight adjusted for gestational age and newborn gender. Multiple linear regression analysis was performed to investigate the relationship between embryo quality and neonatal birthweight after adjustment for some potential confounders.

Main results and the role of chance: In the primary multivariable model, singletons from the poor-quality blastocyst group weighed 183.5 g less than those from the excellent-quality blastocyst group (95% CI: -295.1 to -71.9 g, P = 0.001) in terms of mean birthweight after accounting for patient characteristics, IVF treatment parameters, the year of treatment and newborn gender. Likewise, poor-quality blastocyst transfer was associated with lower gestation-adjusted Z-scores than the transfer of excellent-quality blastocysts (β = -0.35, 95% CI: -0.59 to -0.12, P = 0.003).

Limitations and reasons for caution: The current study was limited by its retrospective design and the fact that our analysis was restricted to women with singleton births from single blastocyst transfers. Future prospective studies are required to confirm our findings.

Wider implications of the findings: Our findings provide new insight into the relationship between embryo quality and neonatal outcomes by showing that poor-quality blastocyst transfer was associated with a decrease in singleton birthweight.

Study funding/competing interest(s): This study was supported by the National Key Research and Development Program of China (grant no. 2018YFC1003000), the National Natural Science Foundation of China (grant nos. 81771533, 81571397 and 31770989), and the China Postdoctoral Science Foundation (Grant no. 2018M630456). The authors have no conflicts of interest to declare.

Trial registration number: Not applicable.

Keywords: birthweight; blastocyst; embryo quality; frozen-embryo transfer; vitrification.