Sex-related growth differences are present but not enhanced in in vitro fertilization pregnancies

Objective: To determine whether IVF modifies the effect of fetal sex on growth.

Design: Retrospective cohort study.

Setting: Tertiary care center and related facilities.

Patient(s): Singleton live births without fetal/maternal comorbidities from fertile women who conceived without the use of assisted reproductive technologies and infertile women who conceived with IVF.

Intervention(s): None.

Main outcome measure(s): The primary outcome was birth weight (BW). Secondary outcomes were fetal crown-rump length (CRL) in the first trimester, biparietal diameter (BPD), and estimated fetal weight (EFW) in the second trimester.

Result(s): There were no differences in baseline characteristics between women carrying male fetuses and those carrying female fetuses in either mode of conception. In unadjusted analyses, the male-female differentials in fetal BPD and BW were more pronounced in the IVF cohort than in the unassisted cohort. In multivariable regression analysis, male BPD exceeded female BPD by 0.12 cm, male EFW exceeded female EFW by 12 g, and male BW exceeded female BW by 172 g. IVF did not have a significant effect on BPD but was associated with a 52 g increase in EFW in the midgestation. IVF was associated with an 81-g reduction in BW. IVF did not modify the magnitude of size differences between the sexes in the midgestation or at birth.

Conclusion(s): Comparable sex-dependent differential growth occurs in unassisted and IVF pregnancies.