Gestational diabetes mellitus (GDM), characterized by maternal high blood sugar, affects up to 15% of pregnancies worldwide. GDM doubles the risk of fetal growth (i.e. macrosomia, large fetus,) which further predisposes the affected fetus to elevated risks of obesity, diabetes and cardiovascular disease later in life. The placenta mediates macrosomia by increasing fat and glucose transport to the fetus during GDM. Effective methods to normalize placental nutrient transport and prevent macrosomia are lacking. Choline is a semi-essential nutrient found in egg yolks, meat, fish and cruciferous vegetables. The demand for this nutrient increases substantially during pregnancy. Previous research demonstrated that maternal choline supplementation (MCS) normalized placental fat and glucose transport as well as fetal growth and fat mass in GDM mice. In this study, the investigators will recruit pregnant women with GDM and randomized them to receive a choline supplement (470mg/day, a dose with demonstrated safety), or a placebo for 8 weeks, starting after gestational week 28. The investigators will determine the effects of choline on fetal growth as well as the influence of choline on placental transport and epigenetic modifications in growth-related genes in the placenta and umbilical cord. Successful completion of this study will provide valuable insights into the use of choline supplement as a modifier of placental macronutrient homeostasis in GDM to improve fetal growth outcomes.