Gestational Diabetes in Primary Care

Paul Hicks, MD

In This Article


Assessment of maternal-fetal well-being in GDM can be divided into the initial evaluation performed at or shortly after diagnosis and longitudinal assessments performed through the duration of the pregnancy.[2] Initial studies include a laboratory evaluation, genetic counseling, and a level II ultrasound. The laboratory evaluation should include measurement of serum creatinine, hemoglobin A1c (HgAlc), and thyroid-stimulating hormone (TSH) levels, as well as a triple screen test (serum human chorionic gonadotropin [hCG] and hCG free beta-subunit tests are used in combination with unconjugated estriol and alpha-fetoprotein in the triple screen test for detecting Down syndrome in the second trimester of pregnancy). The TSH level is obtained because of the association of diabetes with hypothyroidism. The HgAlc, which reflects the level of glucose control in the preceding 6 to 8 weeks, should be normal. An elevated value may reflect pregestational diabetes or glucose intolerance for more than a month before diagnosis. A high value for HgAlc in a woman with pregestational diabetes is associated with fetal loss in the first 20 weeks and congenital malformations[46]; in a woman with GDM, it is associated with macrosomia and fetal death.[32]

Fetal ultrasound assessment is of particular importance in GDM. Ultrasound provides sensitive evaluation of fetal anatomy, which can be of critical value in the case of a woman with heretofore undetected pregestational diabetes. In the case of true GDM, ultrasound provides a measure of fetal weight and amniotic fluid volume.

Buchanan and coworkers[47] report on the use of ultrasound measurements to help guide management. They found that a fetal-abdominal circumference (AC) ≥ 75% for gestational age, measured at 29 to 33 weeks gestation, correlated with an increased risk for birth of an LGA infant. Further, if these mothers were treated with insulin, the incidence of LGA births was similar to that in infants whose ACs were < 75% for gestational age. Unfortunately, the rate of cesarean section in this study was a startling 43% in the insulin treatment group, compared with 14% to 21% in the diet-controlled groups. This unexplained finding makes confirmatory work necessary before an ultrasound-guided treatment strategy can be recommended.

There are 3 interrelated objectives to the longitudinal care plan: control of the diabetes, monitoring for maternal complications, and the prevention of fetal/neonatal complications. Diabetes care continues with control of diet, monitoring of blood glucose levels, and insulin therapy, if indicated. Prepartum complications more common in women with GDM are pregnancy-induced hypertension (PIH) and pre-eclampsia and preterm labor (PTL). Weekly blood pressure and urine protein measurements, as part of routine prenatal care, should provide early indications suggestive of PIH and pre-eclampsia. Preterm labor is defined differently in pregnancies complicated by GDM. There is evidence that fetal hyperinsulinemia retards lung surfactant production and may delay lung maturity, often until 38 weeks gestation. Thus, any confirmed labor before 38 weeks falls under the definition of PTL and requires aggressive management, with consideration of amniocentesis to evaluate lung maturity. Amniotic fluid should be evaluated for the presence of phosphotidyl glycerol, as a lecithin/sphingomyelin (L/S) ratio greater than 2.0 does not always ensure lung maturity in diabetes-affected infants.[48]

Fetal/neonatal complications include those related to the size of the fetus and those related to the severity of diabetes and its effect on the mother. Regarding infant size, no clear evidence shows that any intervention, beyond routine care, is required in persons with diet-controlled diabetes, unless the pregnancy continues to 41 weeks or more.[6] In patients with insulin-requiring diabetes, more intensive monitoring of fetal size and well-being is recommended. Typically, this includes biweekly non-stress tests (NSTs) beginning at 32 to 36 weeks, with follow-up as appropriate.

It is important to remember that perceived fetal size is a function of actual fetal weight, maternal weight, and the presence of polyhydramnios (more common in women with GDM) or absence. Unfortunately, the estimation of fetal weight (EFW) is notoriously inexact whether determined on the basis of Leopold's maneuvers or ultrasound. Any pregnancy with fetus size greater than normal for gestational age, or with suspected macrosomia or polyhydramnios, warrants ultrasound evaluation; however, no evidence clearly shows that routine ultrasonography at term is useful for the detection of macrosomic infants.[49] In pregnancies that go beyond 41 weeks, however, an ultrasound may provide useful information.

When diabetes has been well controlled and there are no maternal complications, fetal weight is the major factor that determines whether intervention is appropriate before the onset of spontaneous labor. For suspected normal-weight fetuses, no convincing evidence supports routine induction or other intervention before 41 to 42 weeks. Some have advocated earlier induction, in an attempt to decrease the incidence of macrosomia and shoulder dystocia. It is difficult to estimate fetal weight accurately; therefore, if macrosomia is detected by Leopold's maneuvers or ultrasound, one may feel compelled to intervene with induction or a scheduled cesarean section. Induction is recommended for fetuses ≥ 4000 g and cesarean section for those ≥ 4500 g.[1]


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