Gestational diabetes mellitus (GDM) is hyperglycemia occurring during the second or third trimester in absence of a pre-pregnancy diagnosis of type 1 or type 2 diabetes.

Screening for gestational diabetes mellitus in asymptomatic pregnant women after 24 wk gestation is a grade B recommendation by the U.S. Preventive Services Task Force (USPSTF). In the U.S., a two-step approach to screening is commonly used and is currently endorsed by the American College of Obstetricians and Gynecologists (ACOG) and the National Institutes of Health (NIH). The International Association of Diabetes in Pregnancy Study Group has recommended a simplified, one-step approach for screening and diagnosing GDM, which has been endorsed by the American Diabetes Association since 2011, with the acknowledgment that the one-step approach increases the prevalence of GDM without clear evidence of benefit. Pregnant women with diabetes mellitus (DM) (gestational or preexisting) are classified according to White classification (Table 1).

Gestational diabetes

Diet-controlled gestational diabetes (A1)

Medication-treated gestational diabetes (A2)

Suspect GDM if:

• Fetal size greater than dates on Leopold or increased fundal height measurement
• Ultrasound findings of fetal macrosomia (especially enlarged abdominal circumference) or polyhydramnios
• Marked maternal obesity or weight gain above expected range
• Acanthosis nigricans (as underlying insulin resistance increases risk)
• Symptoms of diabetes
• Glucosuria
• Hemoglobin A1c ≥ 5.7 in the first trimester

During normal pregnancy, several mechanisms contribute to increased insulin resistance. Placental secretion of human placental lactogen (hPL) decreases maternal insulin sensitivity, decreases maternal glucose utilization, and increases lipolysis, all to ensure adequate glucose availability to the growing fetus. Maternal pancreatic beta cells are increased in order to secrete additional insulin to compensate for the increased circulating blood glucose. Insulin resistance is also exacerbated by an increase in maternal adipose deposition, decreased exercise, and increased caloric intake. GDM occurs when maternal insulin secretion cannot meet the increased glucose burden, resulting in carbohydrate intolerance and hyperglycemia.

Preexisting type 1 or 2 DM not previously diagnosed

• History with focus on personal medical history, prior pregnancy history, and family history
• Routine prenatal examination
• Laboratory evaluation (see the following)

• Exclude preexisting diabetes.
• For women with risk factors (see above), order a 1-hr glucose tolerance test at the first prenatal visit, then repeat at 24 to 28 wk if initial screen was normal. If abnormal at intake, consider the probability of undiagnosed preexisting DM or underlying insulin resistance and check hemoglobin A1c. A diagnosis of diabetes is made if a woman meets any of the following criteria: Fasting plasma glucose >126 mg/dl, A1c >6.5%, random plasma glucose >200 mg/dl. The authors consider a first-trimester A1c of ≥5.7 suggestive of preexisting insulin resistance and would be inclined to monitor closely for hyperglycemia.
• Two-step approach:
  1. For screening without risk factors, a 1-hr, nonfasting 50-g oral glucose tolerance test (OGTT) is appropriate. If the result is abnormal (≥130 mg/dl, as defined by Carpenter and Coustan), a 3-hr, 100-g oral glucose tolerance test is performed. The diagnosis of GDM is made if two or more of the following glucose values are met or exceeded:
     1. Fasting: 95 mg/dl
     2. 1-hr plasma glucose: 180 mg/dl
     3. 2-hr plasma glucose: 155 mg/dl
     4. 3-hr plasma glucose: 140 mg/dl
  2. If one of four values on 3-hr glucose tolerance test is abnormal, consider repeat testing in 1 mo and recommend a low-carbohydrate diet immediately and consultation with a nutritionist. At least one study has demonstrated increased perinatal risk in women with only one of four abnormal values on 3-hr OGTT.
• One-step approach:
  1. Like the two-step, a one-step screening is performed at 24 to 28 wk on all pregnant patients who have not already been diagnosed with diabetes. This is a 2-hr, 75-g oral glucose tolerance test performed after an overnight, 8-hr fast. A diagnosis of GDM is made if one or more of the following values are met or exceeded:
     1. Fasting: ≥92 mg/dl
     2. 1-hr plasma glucose ≥180 mg/dl
     3. 2-hr plasma glucose ≥153 mg/dl
• After pregnancy, women with GDM have an increased risk of developing diabetes during their lifetime. Women with GDM should be screened at or after 6 wk postpartum with a 75-g, 2-hr GTT to diagnose type 2 diabetes using the same criteria as nonpregnant patients. Alternatively, an HgbA1c can be performed at or after 12 wk postpartum.

Ultrasound for fetal size is performed in women with GDM. It may be initiated at the time of diagnosis and repeated every 3 to 4 wk if macrosomia is suspected. Clinicians should consider local standards of care.

• Glucose monitoring:
  1. Four times daily: Fasting and 2-hr postprandial (defined as 2 hr after the start of each meal)
  2. Goals: Fasting <95 mg/dl; 2-hr postprandial <120 mg/dl
  3. Can also use 1-hr postprandial goal of <140 mg/dl
• Dietary modifications for glycemic control:
  1. Follow a low-carbohydrate diet; avoid sugar and concentrated sweets; and eat small, frequent meals (three meals with two snacks is often recommended).
  2. Complex carbohydrates should be consumed over simple carbohydrates to prevent glucose fluctuations.
  3. Diet should adequately meet the needs of pregnancy (following sublist) while restricting carbohydrates to 33% to 40% of daily calories. Caloric needs in pregnancy:
     1. BMI <30: 30 kcal/kg/day
     2. BMI >30: 25 kcal/kg/day
     3. BMI >40: 12 to 14 kcal/kg/day
  4. Regular moderate exercise, defined as 30 min five times per week.
  5. Ongoing nutrition counseling throughout pregnancy.

Initiate if >20% of glucose values are elevated after trial of diet control:

• Insulin: Considered the gold standard in GDM management
  1. There are no randomized controlled trials on insulin regimens, and therapy is largely guided by expert opinion.
  2. Insulin is the only FDA-approved medication for GDM (Pregnancy Class B) and does not cross placenta.
  3. Insulin may be started first line or added when oral medications have failed to achieve glycemic control. The authors consider factors such as the degree of hyperglycemia, obstacles to medication adherence, and gestational age at time of diagnosis (with early-onset diagnosis more likely to progress and require insulin) when initiating therapy. The ADA recommends insulin as first-line pharmacotherapy for GDM, and ACOG (2017) mirrors this recommendation (Level A).
  4. Regardless of insulin regimen initiated, blood glucose values should be reviewed frequently, and the regimen adjusted and customized to optimize each woman’s blood glucose levels, using a single agent or combination of long, intermediate, and/or short-acting insulins.
  5. One commonly used regimen:
     1. Insulin 0.7 to 1.0 U/kg/day subcutaneous (based on current pregnant weight), with two thirds of the total daily dose given in the morning and one third of the total daily dose given in the evening.
     2. One third of each dose is given as short-acting insulin and the remaining two thirds as long-acting insulin.
• Oral hypoglycemics:
  1. Oral antidiabetic agents continue to be used in the management of GDM, despite a lack of FDA approval for this indication.
  2. Several recent studies have examined the potential benefits and harms of metformin and glyburide, comparing them with the gold-standard insulin and with each other. Metformin (compared with insulin) has been demonstrated to decrease maternal glucose levels, maternal weight gain, and the risk of gestational hypertension. Evidence grows that it may decrease the risk of preeclampsia as well. Although known to cross the placenta, concerns about the long-term risk in exposed offspring have been mitigated by at least one recent study showing no neurodevelopmental differences with intrauterine exposure to metformin versus insulin. Meanwhile, recent meta-analyses have demonstrated worse neonatal outcomes with the use of glyburide compared with insulin. With both metformin and glyburide, many women go on to require insulin therapy.
  3. As of 2017, ACOG recommends “in women who decline insulin therapy or for those women whom the obstetrician or obstetric care provider believes the patient will be unable to safely administer insulin, metformin is a reasonable second-line choice” (Level B); while suggesting that glyburide should not be recommended as a first-line agent due to a failure to achieve equivalent outcomes to insulin in most studies (also Level B).
  4. Metformin: Begin at 500 mg PO nightly or bid, and titrate up to a maximum of 2500 mg daily in divided doses.
  5. Glyburide: Begin at 2.5 mg qd, and titrate up to a maximum of 20 mg qd (10 mg bid). Increase dose as needed by 2.5 to 5 mg/wk.

Antepartum testing is recommended for women with pregestational diabetes and gestational diabetes. There is no consensus regarding initiation, frequency, or modality of antepartum testing in gestational diabetes, and this should be guided by local standards.

• Weekly nonstress test/amniotic fluid level beginning at 32 wk or when medications are initiated in women with GDMA2. Less frequent testing or delayed initiation of testing may be considered in women who maintain glycemic control with diet alone (GDMA1), as increased rates of stillbirth have not been observed in these women before 40 wk of gestation.
• Preexisting or poorly controlled diabetes, vascular complications, or concomitant hypertension: Twice weekly NST/AFI beginning at 28 wk. Consider hospital admission to obtain glycemic control.

• Women with preexisting diabetes should be induced at 39 wk.
• Women with GDMA2 may also be induced at 39 wk unless otherwise indicated, with decisions regarding induction guided by local standards of care.
• In women with GDMA1, ACOG supports expectant management of up to 40 and 6/7 wk with appropriate antepartum testing.
• Counsel regarding elective cesarean section at or after 39 wk if estimated fetal weight is over 4500 g.
• Consider delivery earlier than 39 wk if poor glycemic control or other medical indications such as growth restriction or preeclampsia.

• Goal is normoglycemia (80 to 120 mg/dl) using insulin and D5 lactated Ringer IV fluid if needed.
• Monitor glucose every 1 to 2 hr in active labor.
• Preparation for shoulder dystocia.
• If on glyburide, discontinue in labor or 12 hr before a scheduled induction.
• If on insulin, consider decreased long-acting insulin by one third to one half before scheduled induction. Most experts recommend holding insulin entirely the morning of a scheduled cesarean delivery.

• Class A2: Check fasting blood glucose level before discharge; if abnormal, continue checking at home and schedule early follow-up with primary care physician to confirm diagnosis of DM.
• 6-wk postpartum visit: Screen for impaired glucose tolerance and diabetes with a 75-g, 2-hr glucose tolerance test. Alternatively, an HgbA1c or 3 fasting blood glucose levels may be performed at or after 12 wk postpartum.
• If no evidence of DM, screen annually for DM and counsel on risk factor modification.

• Nutritionist
• Maternal-fetal medicine
• Diabetes educator
• Nurse care manager, when available

• Maternal: Preeclampsia, future type 2 DM or GDM, operative delivery
• Fetal: Polyhydramnios, macrosomia, congenital malformations, shoulder dystocia, birth trauma, intrauterine fetal demise
• Neonatal: Hypoglycemia, hypocalcemia, hyperbilirubinemia, polycythemia, perinatal death, respiratory distress, future obesity, and DM

Regular exercise, maintenance of ideal body weight, and high-fiber low-glycemic diet

Gestational Diabetes (Patient Information)

Diabetes Mellitus (Related Key Topic)