An examination of mediation by DNA methylation on birthweight differences induced by assisted reproductive technologies

Abstract

Background: Children born after assisted reproductive technologies (ART) differ in birthweight from those naturally conceived. It has been hypothesized that this might be explained by epigenetic mechanisms. We examined whether cord blood DNA methylation mediated the birthweight difference between 890 newborns conceived by ART (764 by fresh embryo transfer and 126 frozen thawed embryo transfer) and 983 naturally conceived newborns from the Norwegian Mother, Father, and Child Cohort Study (MoBa). DNA methylation was measured by the Illumina Infinium MethylationEPIC array. We conducted mediation analyses to assess whether differentially methylated CpGs mediated the differences in birthweight observed between: (1) fresh embryo transfer and natural conception and (2) frozen and fresh embryo transfer.

Results: We observed a difference in birthweight between fresh embryo transfer and naturally conceived offspring of - 120 g. 44% (95% confidence interval [CI] 26% to 81%) of this difference in birthweight between fresh embryo transfer and naturally conceived offspring was explained by differences in methylation levels at four CpGs near LOXL1, CDH20, and DRC1. DNA methylation differences at two CpGs near PTGS1 and RASGRP4 jointly mediated 22% (95% CI 8.1% to 50.3%) of the birthweight differences between fresh and frozen embryo transfer.

Conclusion: Our findings suggest that DNA methylation is an important mechanism in explaining birthweight differences according to the mode of conception. Further research should examine how gene regulation at these loci influences fetal growth.

Keywords: Assisted reproductive technology; Birthweight; DNA methylation; MBRN; MoBa.

Fig. 1

Selection of study participants

Fig. 2

Differentially methylated CpGs between newborns conceived naturally and by fresh embryo transfer and birthweight-associated CpGs. a Manhattan plot displaying the 237 differentially methylated CpGs between newborns conceived naturally and those conceived by fresh embryo transfer. The red dotted line refers to the Bonferroni threshold (P = 0.05/770,564). Adjustment variables include maternal age, smoking status, pre-pregnancy BMI, parity, offspring sex, and plate number. b Quantile–quantile plot showing the birthweight-associated CpGs among the 237 fresh embryo transfer-associated CpGs. The yellow dots refer to the CpGs that were also associated with birthweight. Adjustment variables include those mentioned in (a) and maternal education and intake of folic acid. c Quantile–quantile plot showing the interactions of fresh embryo transfer and CpGs on birthweight. Adjustment variables were those mentioned in (b)

Fig. 3

Differentially methylated CpGs between newborns conceived by fresh and frozen embryo transfer and birthweight-associated CpGs. a Manhattan plot displaying the 78 differentially methylated CpGs (P_FDR < 0.05) between the newborns conceived by fresh embryo transfer (n = 764) and frozen thawed embryo transfer (n = 126). The red dotted line refers to the Bonferroni threshold (P = 0.05/770,564), whereas the other dotted line in black refers to the FDR threshold. Adjustment variables include maternal age, smoking status, pre-pregnancy BMI, parity, offspring sex, and plate number. b Quantile–quantile plot showing the birthweight-associated CpGs among the 78 frozen thawed embryo transfer-associated CpGs. The yellow dots refer to the CpGs that were also associated with birthweight. Adjustment variables include those mentioned in (a) and maternal education and intake of folic acid supplement. c Quantile–quantile plot showing the interactions of frozen thawed embryo transfer (fresh embryo transfer as a reference) and CpGs on birthweight. Adjustment variables were those mentioned in (b)