Recent studies implicate maternal gestational diabetes mellitus (GDM) in differential methylation of infant DNA. Folate and vitamin B12 play a role in DNA methylation, and these vitamins may also influence GDM risk. The aims of this study were to determine folate and vitamin B12 status in obese pregnant women and investigate associations between folate and vitamin B12 status, maternal dysglycaemia and neonatal DNA methylation at cytosine-phosphate-guanine sites previously observed to be associated with dysglycaemia. Obese pregnant women who participated in the UK Pregnancies Better Eating and Activity Trial were included. Serum folate and vitamin B12 were measured at the oral glucose tolerance test (OGTT) visit. Cord blood DNA methylation was assessed using the Infinium MethylationEPIC BeadChip. Regression models with adjustment for confounders were used to examine associations. Of the 951 women included, 356 (37.4%) were vitamin B12 deficient, and 44 (4.6%) were folate deficient. Two-hundred and seventy-one women (28%) developed GDM. Folate and vitamin B12 concentrations were not associated with neonatal DNA methylation. Higher folate was positively associated with 1-h plasma glucose after OGTT (β = 0.031, 95% CI 0.001–0.061, p = 0.045). There was no relationship between vitamin B12 and glucose concentrations post OGTT or between folate or vitamin B12 and GDM. In summary, we found no evidence to link folate and vitamin B12 status with the differential methylation of neonatal DNA previously observed in association with dysglycaemia. We add to the evidence that folate status may be related to maternal glucose homoeostasis although replication in other maternal cohorts is required for validation.

Adolescents are at a greater risk of adverse pregnancy outcome, including spontaneous preterm delivery and fetal growth restriction, and typically have a poorer-quality diet than adults have. In the present study, we addressed the hypothesis that low maternal dietary intake of n-3 long-chain PUFA (LCP) status adversely influences pregnancy outcome. A total of 500 adolescents (14–18 years) were recruited at ≤ 20 weeks' gestation. The frequency of consumption of oily fish was determined by questionnaire (at recruitment and during the third trimester). The fatty acid composition of plasma lipids during the third trimester was determined in 283 subjects. Principal components analysis (PCA) was used to derive components, which were divided into tertiles. The pregnancy outcomes were then compared by tertile, adjusting for potentially confounding variables. Of the participants, 69 % reported never eating oily fish during pregnancy, although consumption was not associated with a shorter duration of gestation (P = 0·33), lower customised birth weight (P = 0·82) or higher incidence of small-for-gestational age (SGA) birth (P = 0·55). PCA of the fatty acid composition of maternal plasma lipids identified a ‘low PUFA:SFA (P:S) ratio’ component and a ‘high n-3 LCP’ component. There were no differences between tertiles of the ‘high n-3 LCP’ component and gestational age at delivery (P = 0·62), customised birth weight (P = 0·38) or incidence of SGA birth (P = 0·25), nor were there any associations between the ‘low P:S’ ratio component and pregnancy outcome. Lower proportions of n-3 LCP in plasma lipids are not associated with greater risk of adverse pregnancy outcomes in UK adolescents.