The length of the embryo culture in assisted reproductive technology does not have a major impact on newborn DNA methylation.

Blastocyst culture is an essential part of IVF/ICSI treatments, however, it has been shown to increase the risk of preterm deliveries as well as large for gestational age infants. The effect of the extended culture on offspring phenotype is thought to be mediated by epigenetic mechanisms, since this developmental period coincides with extensive epigenetic remodelling. Here, we compare genome-wide DNA methylation of cord blood and umbilical cord artery samples collected from newborns resulting from cleavage-stage transfer (n = 25), blastocyst-stage transfer (n = 25), and spontaneous conception (n = 30). Epigenome-wide association studies, global methylation analyses, and epigenetic age comparison did not reveal statistically significant differences between the cleavage-stage and blastocyst-stage groups. However, we identified some loci with a >10% difference in median methylation level between the groups, which should be studied further with a larger sample size. The genome-wide DNA methylation of spontaneously conceived and cleavage-stage newborns were comparable while in the spontaneous to blastocyst-stage comparison, cg25263722 was differentially methylated (P = 5 × 10-8) in umbilical cord artery. Our study did not identify major effects of extended culture on DNA methylation, which is reassuring with respect to the future health of newborns conceived via assisted reproductive technologies.