EMBRYO quality and pregnancy outcomes among infertile patients undergoing in vitro fertilisation-embryo transfer (IVF-ET)-assisted pregnancy may be more favourable in the springtime, according to a 2026 retrospective cohort study.
In infertile patients undergoing controlled ovarian stimulation with an antagonist protocol, the rate of blastocyst formation in the spring was higher than that in the summer.
These findings align with emerging research establishing that spring IVF cycles show higher full-term and live birth rates than winter, but an increased risk of early miscarriage.
IVF-ET at the Affiliated Hospital of Southwest Medical University
Researchers retrospectively analysed data from more than 1,400 infertile patients who received IVF and antagonist ovulation induction programme in the Reproductive Medicine Center, Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, China from January 2019 to December 2023.
Participants were divided into spring, summer, autumn, and winter groups and embryo status and pregnancy outcomes were compared.
Favourable Pregnancy Outcomes in Spring Cohorts
Notably, there were no significant differences in general data, embryo quality, and pregnancy outcomes across the four cohorts: season did not significantly affect the positive rate of human chorionic gonadotropin (HCG), clinical pregnancy rate, miscarriage rate, and live birth rate.
However, after adjusting for confounding factors, the blastocyst formation rate in spring was significantly higher than in summer.
By year, in 2020: the blastocyst formation rate was markedly greater in the spring and autumn group than in the winter group.
In 2022, the HCG positive rate was significantly higher in the spring group than in the summer and autumn groups. Further, the clinical pregnancy rate was also considerably greater in the spring and winter groups than in the summer group.
And in 2023, the blastocyst formation rate was, again, significantly higher in the spring (and winter) group than in the autumn cohort.
Possible Clinical Explanations
Authors pointed to the “suitable environmental temperature” in spring possibly regulating the secretion rhythm of oestrogen and progesterone in the body.
Consequently, they suggested, this leads to improved endometrial blood flow that ultimately increases endometrial thickness. It follows that lower temperatures in winter might slow down the growth rate of the endometrium.
Ultimately, stable climatic conditions are reportedly favourable for the healthy development of the endometrium.
Reference
Zhao R et al. Effects of different seasons on the outcome of in vitro fertilization and embryo transfer: a retrospective cohort study. Front Reprod Health. 2026;DOI:10.3389/frph.2026.1782049.
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