PURPOSE: To explore the impact of seasonal variations on the risks of hypertensive disorders of pregnancy (HDP) and gestational diabetes mellitus (GDM) in women who undergo in vitro fertilization (IVF) treatment. METHODS: We retrospectively included a total of 21,469 women who achieved singleton delivery during their first cycles of IVF, the risks of HDP and GDM were compared in different seasonal groups according to the time of embryo transfer and the time of oocyte retrieval. RESULTS: After adjustment via multivariable logistic regression, women who underwent embryo transfer in spring with the expected date of confinement in winter had a higher risk of HDP (4.9% vs. 3.8%
adjusted odds ratio (aOR), 1.34
95% confidence interval (CI), 1.09-1.64
P = 0.005) than those underwent embryo transfer in winter with the expected date of confinement in autumn. There were no seasonal variations in the risk of HDP according to the time of oocyte retrieval or in the risk of GDM regardless of the time of embryo transfer or the time of oocyte retrieval. After subgroup analysis, the seasonal variations in the risk of HDP remained in frozen embryo transfer (FET) cycles but not in fresh embryo transfer (FreET) cycles. CONCLUSIONS: The risk of HDP was increased in women who underwent embryo transfer in spring compared to those who underwent embryo transfer in winter. The risk of HDP is more likely to be affected by the season at the time of embryo transfer in FET cycles compared to FreET cycles.