Heterogeneous offspring growth in spontaneous versus in vitro fertilization pregnancies: a retrospective cohort study

Observational studies suggest that children conceived via in vitro fertilization and embryo transfer (IVF-ET) may exhibit altered growth patterns compared to spontaneously conceived children. This study aimed to compare early physical development among children from different modes of conception and to evaluate the specific effects of frozen versus fresh embryo transfer.

Data from 5,821 children born between 2010 and 2021 were obtained from the Jiangsu Maternal and Child Health Platform, including 2,958 spontaneous conceptions (SC), 2,148 frozen embryo transfers (FET), and 715 fresh embryo transfers (fresh ET). Anthropometric development was assessed from birth to 5 years of age using longitudinal linear mixed-effects models, stratified by singleton and twin pregnancies. Birth outcomes were analyzed secondarily.

Compared to SC among singletons, FET was associated with higher weight (mean difference [MD] 0.14 kg, 95% CI 0.07-0.20), weight gain velocity (MD 0.01 kg/month), BMI z-score, and weight-for-height z-score (WHZ). Fresh ET increased weight and height gain velocities (MD 0.007 kg/month and 0.02 m/month, respectively) without affecting final weight, BMI z-score, or WHZ. Among twins, FET significantly increased weight (MD 0.68 kg, 95% CI 0.28-1.08), weight gain velocity, BMI z-score, and WHZ, while fresh ET only elevated weight gain velocity and BMI z-score. Neither transfer type influenced height gain in twins.

This study identified distinct early childhood growth patterns, with FET associated with increased weight gain and higher BMI/WHZ scores compared to spontaneous conception. These findings underscore the value of growth monitoring in children conceived by assisted reproductive technology.