Early pregnancy exposure to higher glucose levels results in enhanced rates of abortion and an increased incidence of congenital anomalies. Neonates whose mothers have higher glucose levels over a longer duration of pregnancy have higher incidences of macrosomia, hypoglycemia, hypocalcemia, polycythemia, respiratory difficulties, cardiomyopathy, and congestive heart failure. Long-term control of maternal glucose is associated with a reduction in all of these complications.

Macrosomic babies have increasing intolerance to intrauterine compromise as well as an enhanced rate of birth trauma. Respiratory distress syndrome and transient tachypnea are increased in infants of poorly controlled diabetics. In fact, all organ maturation is delayed in direct relation to the degree of hyperglycemia. This may be compounded by impairment of maternal vascular flow to the developing fetus. Infants of inadequately controlled diabetic mothers have an increase in cardiomyopathy and congestive heart failure due to excess glycogen deposition and hypertrophy of the heart muscle as a result of intrauterine compensation for maternal hyperglycemia.

The fetal response to the intrauterine environment such as fetal pancreatic hyperplasia with increased basal insulin secretion can make an impact on the child into adulthood with an increased risk of diabetes. The incidence is increased from that of the familial inheritance; for example, a recent study of Pima Indians showed that there was a greater incidence of diabetes in the offspring of women who had type 2 diabetes during pregnancy than in the offspring of those who developed diabetes years after pregnancy (45% vs. 8.6% at age 20-24 years).