EVIDENCE-BASED ANSWER
No evidence clearly supports the practice of increased fetal surveillance in the pregnancies of women with well-controlled (ie, fasting blood sugar <105 mg/dL) class A1 gestational diabetes (strength of recommendation [SOR]: B, consistent retrospective cohort studies). However, a number of guidelines recommend beginning surveillance of some kind between 32 and 40 weeks based on cumulative risk factors, including gestational diabetes (SOR: C, expert opinion).
CLINICAL COMMENTARY
Follow local standards of care and continue fetal surveillance
Julia Fashner, MD
Piqua, OH
Because malpractice issues weigh heavy in many states, a Family Physician who practices obstetrics may be liable even when a patient is at low risk. We know diabetes has devastating effects on patients. Why would there not be risk with gestational diabetes? The findings in this Clinical Inquiry provide practicing doctors little evidence for or against antenatal testing for women with gestational diabetes. I agree more research is needed to reassure physicians that increased fetal surveillance does not make a difference in fetal or maternal outcomes. Until that time, it would seem prudent to find out what your local standards of care would be—possibly non-stress testing or biophysical profiles during 32 to 40 weeks—and continue your fetal surveillance.
Evidence summary
Gestational diabetes mellitus is diagnosed when at least 2 of 4 values measured in a 3-hour glucose tolerance test are elevated; 2 different definitions of “elevated” are accepted (TABLE 1). White’s classification stratifies the risk of various types of diabetes during pregnancy (TABLE 2): Class A includes patients without a diagnosis of diabetes before pregnancy; classes B, C, and D include patients with pre-existing diabetes of increasing duration; and classes F, H, R, and T include patients with diabetes with various vascular complications.
Infants of mothers with pre-existing diabetes are at increased risk of pre- and neonatal complications (including stillbirth); it has been commonly assumed that type A1 gestational diabetes confers similar risks. However, 2 observational studies call this assumption into question. One study evaluated antepartum predictors of fetal distress requiring a cesarean delivery among 2134 pregnant women with gestational diabetes.4 Antepartum surveillance consisted of biweekly nonstress testing with amniotic fluid index determination starting at 34 weeks gestation. Of the 1501 eligible participants, the study included 810 and 580 class A1 and A2 patients, respectively; the remaining 111 were classes B–T. They considered women with A1 gestational diabetes with fasting plasma glucose levels <105 mg/dL to be well-controlled. Results of antepartum surveillance did not significantly differ among the different diabetic classes.
In univariate and multivariate analyses, the greatest indicator for cesarean section due to fetal distress was a nonreactive non-stress test with decelerations (odds ratio [OR]=5.63; 95% confidence interval [CI], 2.67–11.9). Routine amniotic fluid measurement was not significantly related to either the classification of diabetes or to cesarean delivery for fetal distress. No patients with normal surveillance testing within 4 days of delivery had a stillbirth. However, all 5 stillbirths in the study population occurred among those with A2 diabetes whose last non-stress test was >4 days prior.