Problem Epigenetic age indices are markers of biological aging determined from DNA methylation patterns. Accelerated epigenetic age predicts morbidity and mortality. Women tend to demonstrate slower blood epigenetic aging compared to men, possibly due to female‐specific hormones and reproductive milestones. Pregnancy and the post‐partum period are critical reproductive periods that have not been studied yet with respect to epigenetic aging. The purpose of this paper was to examine whether pregnancy itself and an important pregnancy‐related variable, changes in body mass index (BMI) between pregnancy and the post‐partum period, are associated with epigenetic aging.

Method of Study A pilot sample of 35 women was recruited as part of the Healthy Babies Before Birth (HB3) project. Whole blood samples were collected at mid‐pregnancy and 1 year post‐partum. DNA methylation at both time points was assayed using Infinium 450K and EPIC chips. Epigenetic age indices were calculated using an online calculator.

Results Paired‐sample t‐tests were used to test differences in epigenetic age indices from pregnancy to 1 year after birth. Over this critical time span, women became younger with respect to phenotypic epigenetic age, GrimAge, DNAm PAI‐1, and epigenetic age indices linked to aging‐related shifts in immune cell populations, known as extrinsic epigenetic age. Post‐partum BMI retention, but not prenatal BMI increases, predicted accelerated epigenetic aging.