Birth weight following frozen versus fresh embryo transfer: a retrospective cohort study

ABSTRACT

Objective. Birth weight is an outcome to evaluate the safety of assisted reproductive technology. The objective of this study was to compare the effect of frozen versus fresh embryo transfer on newborn birth weight.
Patients and Methods. In the infertility department of a teaching hospital affiliated with a university of medical sciences, we performed a retrospective cohort study. Eligible women were ≥ 18 years old and conceived a singleton pregnancy (≥ 22 weeks or ≥ 500g) with either frozen or fresh embryo transfer. None of the patients had diabetes, hypertension. We recorded maternal characteristics, newborn features, and perinatal outcomes.
Results. In total, 116 eligible patients with a mean (SD) age of 32.7 (5.8) years and a mean body mass index of 25.6 (2.5) were included. Of these, 84 had a frozen and 32 had a fresh embryo transfer. Mean birth weights were 3,050.7 (587.6) and 2,983.6 (423.5) in the frozen and fresh embryo transfer groups, respectively (p = 0.568). However, after adjusting for confounding factors, including maternal age, gravidity, body mass index, fasting blood sugar, blood pressure, and gestational age, the difference in birth weight was statistically significant [b = 230.8 (103.6), p = 0.003]. There was no statistically significant difference between the two groups in the percentages of low birth weight, small or large for gestational age, preterm, stillbirth, or intra-uterine fetal death singletons.
Conclusions. Frozen embryo transfer results in higher birth weight compared to fresh embryo transfer. This difference was statistically significant despite similar perinatal outcomes, warranting further investigation into underlying mechanisms.