Gestational diabetes is one of the most common complications of pregnancy, affecting about 7 percent of pregnancies each year in the United States. Gestational diabetes is associated with maternal and infant complications, including hypoglycemia, hyper-bilirubinemia, respiratory distress syndrome, preeclampsia, and complications from macrosomia, such as birth trauma (e.g., hemorrhage, perineal tears), cesarean delivery, and operative vaginal delivery.

Up to 60 percent of women diagnosed with gestational diabetes develop type 2 diabetes within 15 years. Therefore, the diagnosis and postpartum management of gestational diabetes have important implications for the prevention of type 2 diabetes. Questions remain, however, about the best ways to assess postpartum risk of diabetes and to screen for diabetes after delivery. To address these questions, the Agency for Healthcare Research and Quality (AHRQ) systematically reviewed the literature on the management of gestational diabetes.

Pharmacologic Management

Few studies have examined the risks and benefits of oral diabetic agents compared with insulin in the treatment of women with gestational diabetes. Because of the limited number of studies and a lack of consistency in the outcomes measured, AHRQ is unable to draw firm conclusions about any of the following treatment comparisons: glyburide (Micronase) versus insulin; glyburide versus insulin versus acarbose (Precose); insulin lispro versus regular insulin; long-acting versus short-acting insulin; and twice-daily versus four-times-daily insulin. Limited evidence shows no substantial clinical differences in maternal or neonatal outcomes with the use of glyburide or insulin lispro compared with insulin. A meta-analysis of three studies that compared insulin with glyburide showed a statistically insignificant decrease in birth weight (93 g [3 oz]) among infants of women treated with insulin. No evidence is available on differences in maternal or neonatal outcomes based on glucose levels at treatment initiation.

Delivery Complications

Little evidence exists on the use of estimated fetal weight or gestational age to guide physicians in making decisions about the timing of labor induction or elective cesarean delivery. One study found that, compared with expectant management, active induction of labor at 38 weeks' gestation reduced birth weight (3,672 versus 3,446 g [8 lb, 2 oz versus 7 lb, 10 oz]; P < .01) and rates of macrosomia (27 versus 15 percent; P = .05), with no concomitant increase in cesarean delivery rates (25 percent in the active induction group versus 31 percent in the expectant management group; P = .43). Although these results suggest that maternal outcomes may be better in women who undergo elective induction, AHRQ is unable to draw firm conclusions based on this single trial.

Risk Assessment for Type 2 Diabetes

There is consistent evidence that anthropometric measures (i.e., weight, body mass index [BMI], and waist circumference) before pregnancy and during the antepartum and postpartum periods are associated with the development of type 2 diabetes. Waist circumference and BMI are the strongest predictors of type 2 diabetes in women with gestational diabetes. Early gestational age at diagnosis (less than 24 weeks) and the use of insulin instead of dietary interventions are the key pregnancy-related clinical factors associated with the development of type 2 diabetes. Physiologic measures, including fasting blood glucose levels and two-hour plasma glucose levels during the diagnostic oral glucose tolerance test (OGTT), are also associated with the development of type 2 diabetes. Higher blood glucose levels after a screening 50-g glucose challenge test and a history of gestational diabetes are associated with the development of type 2 diabetes, but the strength of the associations is not consistent. There are conflicting data on whether the use of progesterone-only contraceptives affects the risk of developing type 2 diabetes. One study found that elevated postpartum homocysteine levels are positively associated with type 2 diabetes.

Postpartum Diagnosis of Type 2 Diabetes

Several studies have found poor physician compliance with postpartum screening for type 2 diabetes in women with a history of gestational diabetes. With the increasing prevalence of childbearing among older women, pregnant women often receive care from an obstetrician and a primary care physician. Whereas obstetricians may provide immediate postpartum screening, family physicians or other primary care physicians will likely provide long-term follow-up. Therefore, an interdisciplinary dialogue among physicians is necessary to influence future care.

Compared with the 75-g OGTT, measurement of fasting blood glucose levels has high specificity, but the sensitivity varies among studies. As a result of heterogeneity in the study design, the recruited population, and the interval of follow-up testing, AHRQ was unable to draw firm conclusions about the performance characteristics of the fasting blood glucose test in women with a history of gestational diabetes. There is also insufficient evidence of test reproducibility. Until the appropriate intervals for follow-up testing are realized, future investigations would benefit from an interdisciplinary clinical approach.

Implications

The results of the AHRQ review have important implications for clinical practice and public health policy. Physicians should be aware that the available data, although limited, do not suggest that there are adverse maternal or neonatal outcomes associated with the use of oral diabetic agents, insulin lispro, or various insulin regimens. The effectiveness of insulin analogues or glyburide in achieving maternal glucose targets or preventing episodes of maternal or neonatal hypoglycemia remains unclear. Several measures of maternal and neonatal morbidity (e.g., perineal tears, operative vaginal delivery) have not been evaluated, and several measures have been evaluated in only one or two studies. Also, it is unclear what glucose thresholds should be used to initiate therapy with insulin, insulin analogues, or glyburide.

Physicians should also be aware that there is insufficient evidence to develop clear guidelines for labor induction or elective cesarean delivery in women with gestational diabetes.