Find information on medical topics, symptoms, drugs, procedures, news and more, written for the health care professional.

* This is the Professional Version. *

Diabetes Mellitus in Pregnancy (Gestational Diabetes)

by Lara A. Friel, MD, PhD

Pregnancy aggravates preexisting type 1 ( insulin -dependent) and type 2 (non– insulin -dependent) diabetes but does not appear to exacerbate diabetic retinopathy, nephropathy, or neuropathy.

Gestational diabetes (diabetes that begins during pregnancy) can develop in overweight, hyperinsulinemic, insulin -resistant women or in thin, relatively insulin -deficient women. Gestational diabetes occurs in at least 5% of all pregnancies, but the rate may be much higher in certain groups (eg, Mexican Americans, American Indians, Asians, Indians, Pacific Islanders). Women with gestational diabetes are at increased risk of type 2 diabetes in the future.

Diabetes during pregnancy increases fetal and maternal morbidity and mortality. Neonates are at risk of respiratory distress, hypoglycemia, hypocalcemia, hyperbilirubinemia, polycythemia, and hyperviscosity. Poor control of preexisting or gestational diabetes during organogenesis (up to about 10 wk gestation) increases risk of major congenital malformations and spontaneous abortion. Poor control of diabetes later in pregnancy increases risk of fetal macrosomia (usually defined as fetal weight > 4000 g or > 4500 g at birth), preeclampsia, spontaneous abortion, and shoulder dystocia. However, gestational diabetes can result in fetal macrosomia even if blood glucose is kept nearly normal.

Diagnosis

  • Oral glucose tolerance test (OGTT) or a single plasma glucose measurement (fasting or random)

Most experts recommend that all pregnant women be screened for gestational diabetes (see Approach to the Pregnant Woman and Prenatal Care:Laboratory testing). An OGTT is usually recommended, but the diagnosis can probably be made based on a fasting plasma glucose of > 126 mg/dL (> 6.9 mmol/L) or a random plasma glucose of > 200 mg/dL (> 11 mmol/L).

The recommended screening method has 2 steps. The first is a screening test with a 50-g oral glucose load and a single measurement of the glucose level at 1 h. If the 1-h glucose level is > 130 to 140 mg/dL (> 7.2 to 7.8 mmol/L), a second, confirmatory 3-h test is done using a 100-g glucose load (see Table: Glucose Thresholds for Gestational Diabetes Using a 3-h Oral Glucose Tolerance Test*).

Most organizations outside the US recommend a single-step, 2-h test.

Glucose Thresholds for Gestational Diabetes Using a 3-h Oral Glucose Tolerance Test*

Organization

Fasting mg/dL (mmol/L)

1-h mg/dL (mmol/L)

2-h mg/dL (mmol/L)

3-h mg/dL (mmol/L)

Carpenter and Coustan

95 (5.3)

180 (10)

155 (8.6)

140 (7.8)

National Diabetes Data Group

105 (5.8)

190 (10.5)

165 (9.1)

145 (8)

*A 100-g glucose load is used.

Treatment

  • Close monitoring

  • Tight control of blood glucose

  • Management of complications

Preconception counseling and optimal control of diabetes before, during, and after pregnancy minimize maternal and fetal risks, including congenital malformations. Because malformations may develop before pregnancy is diagnosed, the need for constant, strict control of glucose levels is stressed to women who have diabetes and who are considering pregnancy (or who are not using contraception).

To minimize risks, clinicians should do all of the following:

  • Involve a diabetes team (eg, physicians, nurses, nutritionists, social workers) and a pediatrician

  • Promptly diagnose and treat complications of pregnancy, no matter how trivial

  • Plan for delivery and have an experienced pediatrician present

  • Ensure that neonatal intensive care is available

In regional perinatal centers, specialists in management of diabetic complications are available.

During pregnancy

Women with type 1 or 2 should monitor their blood glucose levels at home. During pregnancy, normal fasting blood glucose levels are about 76 mg/dL (4.2 mmol/L).

Goals of treatment are

  • Fasting blood glucose levels at < 95 mg/dL (< 5.3 mmol/L)

  • 2-h postprandial levels at ≤ 120 mg/dL (≤ 6.6 mmol/L)

  • No wide blood glucose fluctuations

  • Glycosylated Hb (Hb A 1c ) levels at < 8%

Management of Type 1 Diabetes Mellitus* During Pregnancy

Time Frame

Measures

Before conception

Diabetes is controlled.

Risk is lowest if Hb A 1c levels are 8% at conception.

Evaluation includes

  • 24-h urine collection (protein excretion and creatinine clearance) to check for renal complications

  • Ophthalmologic examination to check for retinal complications

  • ECG to check for cardiac complications

Prenatal

Prenatal visits begin as soon as pregnancy is recognized.

Frequency of visits is determined by degree of glycemic control.

Diet should be individualized according to ADA guidelines and coordinated with insulin administration.

Three meals and 3 snacks/day are recommended, with emphasis on consistent timing.

Women are instructed in and should do blood glucose self-monitoring.

Women should be cautioned about the dangers of hypoglycemia during exercise and at night.

Women and their family members should be instructed in glucagon administration.

Hb A 1c level should be checked every trimester.

Antenatal testing with the following should be done weekly from 32 wk to delivery (or earlier if indicated):

  • Nonstress tests

  • Biophysical profiles

  • Kick counts

Amount and type of insulin should be individualized. In the am ; two thirds of the total dose (60% NPH, 40% regular) is taken; in the pm ; one third (50% NPH, 50% regular) is taken. Or, women can take NPH insulin bid and insulin aspart immediately before breakfast, lunch, and dinner.

During labor and delivery

Vaginal delivery at term is possible if women have documented dating criteria and good glycemic control.

Amniocentesis is not done unless indicated for another problem or requested by the couple.

Cesarean delivery should be reserved for obstetric indications or fetal macrosomia (> 4500 g), which increases risk of shoulder dystocia.

Delivery should occur by 39 wk.

During delivery, a constant low-dose insulin infusion is usually preferred, and the usual sc administration of insulin is stopped. If induction is planned, the usual pm NPH insulin dose is given on the day before induction.

Postpartum and continuing diabetes care should be arranged.

Postpartum insulin requirements may decrease by up to 50%.

* Guidelines are only suggested; marked individual variations require appropriate adjustments.

Normal values may differ depending on laboratory methods used.

Some hospital programs recommend up to 4 insulin injections daily. Continuous sc insulin infusion, which is labor-intensive, can sometimes be given in specialized diabetes clinics.

ADA = American Diabetes Association; Hb A 1c =glycosylated Hb; NPH= neutral protamine Hagedorn.

Management of Type 2 Diabetes Mellitus* During Pregnancy

Time Frame

Measures

Before conception

Hyperglycemia is controlled.

Risk is lowest if Hb A 1c levels are 8% at conception.

Weight loss is encouraged if BMI is >27 kg/m 2 .

The diet should be low in fat, relatively high in complex carbohydrates, and high in fiber.

Exercise is encouraged.

Prenatal

For overweight women, diet and caloric intake are individualized and monitored to avoid weight gain of more than about 9 kg (> 20 lb) or, if they are obese, more than about 7 kg (> 16 lb).

Moderate walking after meals is recommended.

Women are instructed in and should do blood glucose self-monitoring.

The 2-h postbreakfast blood glucose level is checked weekly at clinic visits if possible.

Hb A 1c level should be checked every trimester.

Antenatal testing with the following should be done weekly from 32 wk to delivery (or earlier if indicated):

  • Nonstress tests

  • Biophysical profiles

  • Kick counts

Amount and type of insulin is individualized. For obese women, regular insulin is taken before each meal. For women who are not obese, two thirds of the total dose (60% NPH, 40% regular) is taken in the am ; one third (50% NPH, 50% regular) is taken in the pm . Or, women can take NPH bid and insulin aspart immediately before breakfast, lunch, and dinner.

During labor and delivery

Management is the same as for type 1 (see Table: Management of Type 1 Diabetes Mellitus* During Pregnancy).

* Guidelines are only suggested; marked individual variations require appropriate adjustments.

Normal values may differ depending on laboratory methods used.

BMI= body mass index; Hb A 1c =glycosylated Hb; NPH= neutral protamine Hagedorn.

Management of Gestational Diabetes During Pregnancy

Time Frame

Measures

Before conception

Women who have had gestational diabetes in previous pregnancies should try to reach a normal weight and engage in modest exercise.

The diet should be low in fat, relatively high in complex carbohydrates, and high in fiber.

Fasting plasma glucose and Hb A 1c levels should be checked.

Prenatal

Diet and caloric intake are individualized and monitored to prevent weight gain of more than about 9 kg (> 20 lb) or, if women are obese, more than about 7 kg (> 16 lb).

Moderate exercise after meals is recommended.

Antenatal testing with the following should be done weekly from 32 wk to delivery (or earlier if indicated):

  • Nonstress tests

  • Biophysical profiles

  • Kick counts

Insulin therapy is reserved for persistent hyperglycemia (fasting plasma glucose > 95 mg/dL or 2-h postprandial plasma glucose > 120 mg/dL) despite a trial of dietary therapy for 2 wk.

Amount and type of insulin should be individualized. For obese women, regular insulin is taken before each meal. For women who are not obese, two thirds of the total dose (60% NPH, 40% regular) is taken in the am ; one third (50% NPH, 50% regular) is taken in the pm . Or, women can take NPH bid and insulin aspart immediately before breakfast, lunch, and dinner.

During labor and delivery

Vaginal delivery at term is possible if women have a well-documented delivery date and good diabetic control.

Amniocentesis may not be required.

Cesarean delivery should be reserved for obstetric indications or fetal macrosomia (> 4500 g), which increases risk of shoulder dystocia.

Delivery should occur by 39 wk.

Hb A 1c =glycosylated Hb; NPH= neutral protamine Hagedorn.

Insulin is the traditional drug of choice because it cannot cross the placenta and provides more predictable glucose control; it is used for types 1 and 2 diabetes and for some women with gestational diabetes. Human insulin is used if possible because it minimizes antibody formation. Insulin antibodies cross the placenta, but their effect on the fetus is unknown. In some women with long-standing type 1 diabetes, hypoglycemia does not trigger the normal release of counterregulatory hormones (catecholamines, glucagon, cortisol, and growth hormone); thus, too much insulin can trigger hypoglycemic coma without premonitory symptoms. All pregnant women with type 1 should have glucagon kits and be instructed (as should family members) in giving glucagon if severe hypoglycemia (indicated by unconsciousness, confusion, or blood glucose levels < 40 mg/dL [< 2.2 mmol/L]) occurs.

Pearls & Pitfalls

  • All pregnant women with type 1 should have glucagon kits and be instructed (as should their family members) in giving glucagon if severe hypoglycemia occurs.

Oral hypoglycemic drugs (eg, glyburide) are being increasingly used to manage diabetes in pregnant women because of the ease of administration (pills compared to injections), low cost, and single daily dosing. Several studies have shown that glyburide is safe during pregnancy and that it provides control equivalent to that of insulin for women with gestational diabetes. For women with type 2 diabetes before pregnancy, data for use of oral drugs during pregnancy are scant; insulin is most often preferred. Oral hypoglycemics taken during pregnancy may be continued postpartum during breastfeeding, but the infant should be closely monitored for signs of hypoglycemia.

Management of complications

Although diabetic retinopathy, nephropathy, and mild neuropathy are not contraindications to pregnancy, they require preconception counseling and close management before and during pregnancy.

Retinopathy requires that an ophthalmologic examination be done every trimester. If proliferative retinopathy is noted at the first prenatal visit, photocoagulation should be used as soon as possible to prevent progressive deterioration.

Nephropathy , particularly in women with renal transplants, predisposes to pregnancy-induced hypertension. Risk of preterm delivery is higher if maternal renal function is impaired or if transplantation was recent. Prognosis is best if delivery occurs 2 yr after transplantation.

Congenital malformations of major organs are predicted by elevated Hb A 1c levels at conception and during the first 8 wk of pregnancy. If the level is 8.5% during the 1st trimester, risk of congenital malformations is significantly increased, and targeted ultrasonography and fetal echocardiography are done during the 2nd trimester to check for malformations. If women with type 2 diabetes take oral hypoglycemic drugs during the 1st trimester, fetal risk of congenital malformations is unknown (see Table: Some Drugs With Adverse Effects During Pregnancy).

Labor and delivery

Certain precautions are required to ensure an optimal outcome.

Timing of delivery depends on fetal well-being. Women are told to count fetal movements during a 60-min period daily (fetal kick count) and to report any sudden decreases to the obstetrician immediately. Antenatal testing (see Fetal Monitoring) is begun at 32 wk; it is done earlier if women have severe hypertension or a renal disorder or if fetal growth restriction is suspected. Amniocentesis to assess fetal lung maturity may be necessary for women with the following:

  • Obstetric complications in past pregnancies

  • Inadequate prenatal care

  • Uncertain delivery date

  • Poor glucose control

  • Poor adherence to therapy

Type of delivery is usually spontaneous vaginal delivery at term. Risk of stillbirth and shoulder dystocia increases near term. Thus, if labor does not begin spontaneously by 39 wk, induction is often necessary; also, delivery may be induced between 37 to 39 wk without amniocentesis if adherence to therapy is poor or if blood glucose is poorly controlled. Dysfunctional labor, fetopelvic disproportion, or risk of shoulder dystocia may make cesarean delivery necessary.

Blood glucose levels are best controlled during labor and delivery by a continuous low-dose insulin infusion. If induction is planned, women eat their usual diet the day before and take their usual insulin dose. On the morning of labor induction, breakfast and insulin are withheld, baseline fasting plasma glucose is measured, and an IV infusion of 5% dextrose in 0.45% saline solution is started at 125 mL/h, using an infusion pump. Initial insulin infusion rate is determined by capillary glucose level. Insulin dose is determined as follows:

  • Initially: 0 units for a capillary level of < 80 mg/dL (< 4.4 mmol/L) or 0.5 units/h for a level of 80 to 100 mg/dL (4.4 to 5.5 mmol/L)

  • Thereafter: Increased by 0.5 units/h for each 40-mg/dL (2.2-mmol/L) increase in glucose level over 100 mg/dL up to 2.5 units/h for levels > 220 mg/dL (> 12.2 mmol/L)

  • Every hour during labor: Measurement of glucose level at bedside and adjustment of dose to keep the level at 70 to 120 mg/dL (3.8 to 6.6 mmol/L)

  • If the glucose level is significantly elevated: Possibly additional bolus doses

For spontaneous labor, the procedure is the same, except that if intermediate-acting insulin was taken in the previous 12 h, the insulin dose is decreased. For women who have fever, infection, or other complications and for obese women who have type 2 and have required > 100 units of insulin/day before pregnancy, the insulin dose is increased.

Postpartum

After delivery, loss of the placenta, which synthesizes large amounts of insulin antagonist hormones throughout pregnancy, decreases the insulin requirement immediately. Thus, women with gestational diabetes and many of those with type 2 require no insulin postpartum. For women with type 1, insulin requirements decrease dramatically but then gradually increase after about 72 h.

During the first 6 wk postpartum, the goal is tight glucose control. Glucose levels are checked before meals and at bedtime. Breastfeeding is not contraindicated but may result in neonatal hypoglycemia if oral hypoglycemics are taken. Women who have had gestational diabetes should have a 2-h oral glucose tolerance test with 75 g of glucose at 6 to 12 wk postpartum to determine whether diabetes has resolved.

Key Points

  • Diabetes in pregnancy increases risk of fetal macrosomia, shoulder dystocia, preeclampsia, spontaneous abortion, and, if preexisting or gestational diabetes is poorly controlled during organogenesis, major congenital malformations and spontaneous abortion.

  • Screen all pregnant women for gestational diabetes using an oral glucose tolerance test.

  • Involve a diabetes team if available, and aim to keep fasting blood glucose levels at < 95 mg/dL (< 5.3 mmol/L) and 2-h postprandial levels at ≤ 120 mg/dL (≤ 6.6 mmol/L).

  • Begin antenatal testing at 32 wk and deliver by 39 wk.

  • Adjust insulin dose immediately after delivery of the placenta.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • No US brand name
  • DIABETA, GLYNASE

* This is a professional Version *