75 g glucose tolerance test was provided to all pregnant women during 24-28 weeks.

According to the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria, gestational diabetes mellitus (GDM) was diagnosed when at least one cut point was reached in 2-hour 75-g OGTT test: a fasting plasma glucose (FPG) ≥ 5.1 mmol/L (92 mg/dL), a 1-hour ≥ 10.0 mmol/L (180 mg/dL) or a 2-hour ≥ 8.5 mmol/L (153 mg/dL). Participants were divided into two groups based on OGTT: Group normal glucose tolerant (NGT, n=132) and Group GDM (n=107).

After delivery, participants were further divided into four subgroups based on neonatal birth weight: normal birth weight (NBW) was defined as 2500g ≤ birth weight < 4000g, macrosomia (Mac) was defined as birth weight ≥ 4000g. Group NGT-NBW (n=83): normal glucose tolerant women with normal neonatal birth weight; Group NGT-Mac (n=49): normal glucose tolerant women with macrosomia; Group GDM-NBW (n=82): GDM women with normal neonatal birth weight; Group GDM-Mac (n=25): GDM women with macrosomia.

Investigators performed a genome-wide analysis of DNA methylation in cord blood from macrosomic infants born to women with gestational diabetes or infants with normal birth weight born to normal glucose-tolerant women in order to identify genes related to foetal growth or early adipose tissue development. The candidate genes were then validated using SEQUENOM MassARRAY after bisulfite conversion.