Supraphysiological serum oestradiol negatively affects birthweight in cryopreserved embryo transfers: a retrospective cohort study.

RESEARCH QUESTION: Previous studies have demonstrated a negative relationship between peak oestradiol and low birthweight in IVF. However, it is hard to distinguish which aspect influenced by supraphysiological oestradiol concentrations fundamentally contributes to the low birthweight seen during IVF. This study therefore aimed to investigate whether birthweight was associated with an effect of oestradiol on oocytes.

DESIGN

Oocytes are the only component exposed to the high-oestradiol environment in vitrified-warmed embryo transfer (VET) cycles. A retrospective cohort study of 431 infertile women was therefore carried out to evaluate the relationship between peak oestradiol concentration during controlled ovarian stimulation (COS) and birthweight in full-term singletons born after VET. The effect size was calculated using multivariable regression analysis.

RESULTS

In this cohort, the mean peak oestradiol concentration was 4186.6 ± 1215.0 pg/ml, the mean number of oocytes retrieved was 11.5 ± 5.4, the mean length of ovarian stimulation was 11.3 ± 2.1 days and the mean birthweight was 3441.8 ± 466.1 g. The results indicated that peak oestradiol concentration was negatively correlated with birthweight in full-term singletons born after VET (adjusted β -5.0, 95% confidence interval [CI] -9.2 to -0.7). The effect size indicated that for every 100 pg/ml increase in peak oestradiol concentration, birthweight decreased by 5.0 g. The P for trend value was 0.038.

CONCLUSIONS

Peak serum oestradiol during COS is negatively associated with birthweight. This model proposes a novel concept as well as new evidence that the effect on birthweight is due to the primary influence of a high oestradiol concentration on oocytes during COS.