When considering gestational diabetes diagnosis criteria, carbohydrate intolerance with onset or recognition during pregnancy after 20 weeks is foremost.

Gestational diabetes accounts for about 6 in 7 cases of diabetes in pregnancy. Risk factors are similar to nongestational diabetes: obesity, advanced maternal age, hypertension, family history of diabetes, nonwhite ethnicity and prior macrosomic infant.

Diagnosing gestational diabetes is a two-step process, according to Kendal K. Stephens, M.D., a  maternal-fetal medicine specialist with Norton Children’s Maternal-Fetal Medicine.

The first step is a one-hour, 50-gram glucose challenge test. If the result is elevated at a plasma glucose value greater than 130 milligrams per deciliter (mg/dL) to 140 mg/dL, depending on the community cutoff, the next step is a fasting, three-hour glucose tolerance test.

Diagnosis on the fasting three-hour test with a 100-gram load is based on elevations at any two or more blood testing times — fasting, one hour, two hours or three hours — or a fasting glucose level greater than 126 mg/dL. A one-hour screen greater than 200 mg/dL also confirms the diagnosis of gestational diabetes.

One study found even a single abnormal value during the three-hour glucose tolerance test raised the risk of adverse pregnancy outcomes such as miscarriage, congenital malformations and maternal mortality. For patients who experience such abnormalities, we recommend glycemic monitoring or a repeat three-hour oral glucose tolerance test within four weeks.

Management of gestational diabetes

The same principles of diabetic management are applied for gestational and pre-gestational diabetes.

“The treatment for gestational diabetes is the same, but time is of the essence. If the patient has elevated blood sugars after dieting for one to two weeks, then do not delay initiation of medication,” Dr. Stephens said.

Poorly controlled diabetes increases the risk of congenital anomalies threefold to eightfold. Women with an A1C level over 8.5 have a 22% risk for congenital malformations.

Studies have found miscarriage rates for women with poor glycemic control are 25% to 44%, but approach the general population rate with treatment for gestational diabetes. With treatment, the risk of macrosomia drops from 22% to 13%, and the risk for preeclampsia decreases from 18% to 12%.

Insulin is the gold standard for treatment for diabetes in pregnancy. Insulin does not cross the placenta but does reduce maternal blood sugar and transplacental transport of glucose to the fetus. Fetal blood sugar is typically 15 mg/dL less than maternal blood sugar.

Oral hypoglycemic agents are not well studied in pre-gestational diabetes and should be considered only for those not willing or able to self-administer insulin. All oral agents cross the placenta and worsen neonatal hypoglycemia. Insulin is the standard of care for the treatment of gestational diabetes due to its superior efficacy and safety profile during pregnancy.

The American Association of Clinical Endocrinology recommends a preconception A1C goal of less than 6.5 to mitigate congenital anomaly risks. For that reason, all women of childbearing age with diabetes should be referred for preconception counseling.

Even with excellent glycemic control, mothers with diabetes are at higher risk for hypertension, preeclampsia, cesarean delivery, preterm birth and maternal mortality.

Norton Children’s Maternal-Fetal Medicine initiates antenatal fetal surveillance at 32 weeks or earlier in cases of poor glycemic control, conducting twice-weekly testing. There is no consensus on fetal testing for diet-controlled gestational diabetes; however, it is tailored to individual circumstances, considering factors such as fetal growth and maternal comorbidities.

“We typically do not perform it unless the patient has other pregnancy comorbidities, such as obesity, with a BMI [body mass index] greater than 40,” Dr. Stephens said.

Delivery timing typically is recommended in the 39th week of pregnancy, if on medication, according to Dr. Stephens.

Norton Children’s Maternal-Fetal Medicine offers patients inpatient glycemic control for three to five days prior to delivery, if necessary, as earlier delivery may be required in cases of suboptimal control.

We collaborate closely with our OB/GYN providers and neonatologist colleagues to optimize intrapartum blood sugar management and conduct thorough postnatal evaluations of the newborn.