Trends in DNA Methylation over Time Between Parous and Nulliparous Young Women

TL;DR

This study found that pregnancy and childbirth can either speed up or slow down DNA methylation changes in young women over time.

Contribution

The study identifies specific CpG sites where pregnancy alters the rate of DNA methylation changes compared to non-pregnant women.

Findings

Most CpGs showed decreasing DNA methylation trends over time in both parous and nulliparous women.

Some CpGs showed accelerated or slowed methylation changes in parous women compared to controls.

A small subset of CpGs changed significantly only in nulliparous women.

Abstract

Background/Objectives: The experience of pregnancy and parturition has been associated with long-term health effects in mothers, imparting protective effects against some diseases while the risk of other diseases is increased. The mechanisms that drive these altered disease risks are unknown. This study examined DNA methylation (DNAm) changes from pre-pregnancy to several years after giving birth in parous women compared to nulliparous controls over the same time interval. Methods: Using 180 parous-associated CpGs, three analyses were carried out to test DNAm changes from pre-pregnancy at age 18 years to gestation; from gestation to post-pregnancy at age 26 years in parous women; and from 18 to 26 years in nulliparous women using linear mixed models with repeated measures. Results: The directions of DNAm changes were the same between the parous and nulliparous groups. Most CpG dinucleotides (67%, 121 of 180) had a decreasing trend while a small number (7%, 13 of 180) had an increasing trend. Of the CpGs showing increasing or decreasing DNAm, approximately half had DNAm change to a smaller extent in parous women and the other half changed more in parous women than nulliparous controls. 9% (17 of 180) changed significantly in nulliparous women only, leading to a significant difference in DNAm levels in parous women at the post-pregnancy 26 years time point. Conclusions: Pregnancy and parturition may accelerate methylation changes in some CpGs, but slow down or halt methylation changes over time in other CpGs.

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