- Are oral hypoglycemic agents equivalent to insulin in the treatment of gestational diabetes?
Aaron B. Caughey, MD, PhD; (Examining the Evidence, March 2011)
Gestational diabetes mellitus (GDM) was once thought to be a mild condition that had few lasting consequences. Now, we know that it carries significant short- and long-term implications for women and their offspring. A growing body of evidence suggests that early detection and aggressive monitoring and management of GDM can greatly improve outcomes for pregnant women and their babies. This article outlines the parameters of this approach.
GDM increases maternal risks even after pregnancy
Even mild degrees of hyperglycemia during pregnancy can harm mother and baby. Hyperglycemia is associated with an elevated risk of hypertensive disorders during pregnancy, as well as preterm labor, cesarean delivery, and later metabolic disorders—but there is no obvious threshold of hyperglycemia at which these risks increase.1
GDM is a strong predictor that a woman will later develop type 2 diabetes.2 One study found that GDM increases that risk as much as sevenfold over a woman’s lifetime.3 GDM is also associated with an elevated risk of cardiovascular disease, particularly if the woman has a family history of type 2 diabetes.4
One of the most common and serious types of morbidity affecting infants born to women who have GDM is large size for gestational age, which imparts a significantly elevated risk of injury at the time of vaginal birth and increases the risk of trauma to the mother during cesarean delivery.
GDM is not benign in the fetus, either
Evidence is increasing that GDM raises the risk of adverse clinical consequences in the fetus. The two most frequent and serious types of morbidity affecting infants born to mothers who have GDM are:
- large size for gestational age
- respiratory distress syndrome.7
Infants who are large for gestational age (LGA) face a significantly elevated risk of injury at the time of vaginal birth, such as shoulder dystocia and newborn asphyxia.8 Cesarean delivery is the preferred route for the LGA infant, but it often increases the risk of trauma to the mother, compared with the vaginal route.8
Respiratory distress syndrome, common among premature infants, also affects many infants born to women who have GDM— even near-term infants—because hyperglycemia appears to delay fetal lung maturity.9
Recent studies indicate that exposure to maternal hyperglycemia also increases a child’s risk of long-term complications. Children born to mothers who have GDM have nearly twice the risk of childhood obesity and metabolic syndrome, compared with children born to mothers who do not have GDM.10 In addition, several studies have found that children born to obese mothers who have GDM are more likely to develop type 2 diabetes than are children of non-obese mothers without GDM.3,11
Occasionally, infants of women who have GDM are born with hypoglycemia; this condition arises from an insulin surge in response to maternal hyperglycemia. In an infant, hypoglycemia can lead to seizures and death, and maternal hypoglycemia can cause neuro-psychological deficits in the infant.12
Other health problems related to GDM include jaundice and developmental delays in walking and other motor skills.13
The two-step, 100-g, 3-hour oral glucose tolerance test (OGTT) has been the gold standard for diagnosis of GDM in the United States for many years. However, this approach is expensive—rendering it impractical in some settings. Moreover, reproducibility is only approximately 78%.14
The World Health Organization recently reviewed evidence underlying various diagnostic techniques and recommended a one-step, 2-hour, 75-g OGTT for GDM.14 Another recent review of the literature on the various screening protocols underscores the validity of this approach.15
The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study of more than 23,000 nondiabetic women incorporated the 2-hour, 75-g OGTT.16 Investigators found that elevated glucose levels on this test are highly predictive of birth weight above the 90th percentile and a cord-blood serum C-peptide level above the 90th percentile. However, the test has weaker predictive value for primary cesarean delivery and clinical neonatal hypoglycemia.
Based on the work of HAPO, the American Diabetes Association (ADA) revised its guidelines for diabetes assessment and now recommends that physicians perform a 75-g OGTT at 24 to 28 weeks’ gestation, with plasma glucose measurement in the fasting state and at 1 and 2 hours. A single abnormal level merits a diagnosis of GDM in women not previously diagnosed with overt diabetes.17