Impact of maternal age on birthweight in frozen embryo transfer cycles: an analysis including 12565 singleton newborns

Abstract

Background Previous studies have investigated the effect of maternal age on assisted reproductive technology (ART) success rates. However, little is known about the relationship between maternal age and neonatal birthweight in frozen embryo transfer (FET) cycles. Does maternal age have an impact on singleton birthweight in FET cycles?Methods This retrospective study was conducted at a tertiary care centre, involving singleton live births born to women undergoing frozen-thawed embryo transfer during the period from January 2010 to December 2017. A total of 12565 women who fulfilled the inclusion criteria were enrolled and were grouped into four groups according to the maternal age: <30, 30–34, 35–39, and ≥ 40 years old. Maternal age between 30 and 34 years old was taken as a reference group. Singleton birthweight was the key outcome measure. A multivariable linear regression analysis was conducted to reveal the relationship between maternal age and neonatal birthweight with controlling for a number of potential confounders.Results A modest decrease but no significant difference in birthweight and gestational age- and gender-adjusted birthweight (Z-scores) was observed in maternal age over 35 years old as compared with group with 30–34 years old. Further, multiple linear regression analyses indicated that maternal body mass index (BMI), embryo developmental stage at transfer, parity, number of embryos transferred, FET endometrial preparation, endometrial thickness, gestational age and newborn gender were all independent predictors of neonatal birthweight.Conclusion Grouping with different maternal age was not associated with mean birthweight and Z-scores of singletons resulting from FET.