Background: Several organizations recommend screening pregnant women for gestational diabetes mellitus. Treating substantially elevated fasting glucose levels reduces the risk of fetal macrosomia and perinatal complications, but it is unclear whether treating mild gestational diabetes (e.g., a normal fasting glucose level, but elevated levels within three hours of a glucose challenge) will also improve outcomes. Landon and colleagues studied whether treating mild gestational diabetes effectively reduces perinatal and obstetric complications.

The Study: The authors conducted a prospective randomized trial among women between 24 and 31 weeks of gestation who had been given a three-hour, 100-g oral glucose tolerance test. Women were eligible if they had a fasting glucose level of less than 95 mg per dL (5.3 mmol per L) and at least two subsequently elevated glucose measurements (i.e., greater than 180 mg per dL [10 mmol per L] at one hour, 155 mg per dL [8.6 mmol per L] at two hours, and 140 mg per dL [7.8 mmol per L] at three hours). The control group received standard prenatal care, whereas the treatment group received formal nutritional counseling and diet therapy, with the option to use insulin if required.

Women were excluded if they had preexisting diabetes, an abnormal glucose screening result before 24 weeks of gestation, asthma, hypertension, a history of corticosteroid use, or a history of previous fetal anomalies. Multiple maternal and fetal complication rates were compared between the two groups. The primary outcome was a composite of perinatal mortality and other complications, including neonatal birth trauma, hyperbilirubinemia, and hypoglycemia.

Results: A total of 958 women with similar baseline traits were enrolled and randomized. No significant differences were noted between groups about the primary outcome. However, the incidence of several fetal and maternal complications was reduced in the treatment group (see accompanying table), including the risks of shoulder dystocia and a birth weight of more than 4 kg (8.8 lb). No marked differences were noted in the risks of preterm delivery, being small for gestational age, hypoglycemia, respiratory distress syndrome, or neonatal intensive care unit admission.

Conclusion: The authors conclude that treating mild gestational diabetes reduces a number of maternal and neonatal complications; however, stillbirth and perinatal mortality rates are not affected.