Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Diabetes During Pregnancy

(Gestational Diabetes)


Lara A. Friel

, MD, PhD, University of Texas Health Medical School at Houston, McGovern Medical School

Last full review/revision Jun 2021| Content last modified Jun 2021
Click here for the Professional Version

For women who have diabetes before they become pregnant, the risks of complications during pregnancy depend on how long diabetes has been present and whether complications of diabetes, such as high blood pressure and kidney damage, are present. Pregnancy tends to make diabetes (types 1 and 2) worse but does not trigger or worsen the complications of diabetes (such as eye, kidney, or nerve damage).

(See also Diabetes.)

Gestational diabetes

At least 5% of pregnant women develop diabetes during pregnancy. This disorder is called gestational diabetes. Gestational diabetes is more common among the following:

  • Obese women

  • Women with a family history of diabetes

  • Certain ethnic groups, particularly Native Americans, Pacific Islanders, and women of Mexican, Indian, or Asian descent

Unrecognized and untreated, gestational diabetes can increase the risk of health problems for pregnant women and the fetus and the risk of death for the fetus.

Most women with gestational diabetes develop it because they cannot produce enough insulin. Insulin helps control the level of sugar (glucose) in the blood. More insulin is needed during pregnancy because the placenta produces a hormone that makes the body less responsive to insulin (a condition called insulin resistance). This effect is particularly noticeable late in the pregnancy, when the placenta is enlarging. As a result, the blood sugar level tends to increase. Then, even more insulin is needed.

Some women may have had diabetes before becoming pregnant, but the disease was not recognized until they became pregnant.

Risks of Diabetes During Pregnancy

If poorly controlled, diabetes is more likely to cause problems.

Early in pregnancy, poor control of diabetes increases the risk of the following:

  • Having a baby with major birth defects

  • Having a miscarriage

Late in pregnancy, poor control of diabetes increases the risk of the following:

Babies born to women with diabetes tend to be larger than those born to women without diabetes. If diabetes is poorly controlled, babies may be particularly large. A large fetus is less likely to pass easily through the vagina and is more likely to be injured during vaginal delivery. Consequently, cesarean delivery may be necessary. Also, the fetus’s lungs tend to mature slowly.

Newborns of women with diabetes are at increased risk of having low sugar, low calcium, and high bilirubin levels in the blood (hyperbilirubinemia).

Diagnosis of Diabetes During Pregnancy

  • Blood tests to measure blood sugar

Most experts now recommend that doctors routinely screen all pregnant women for gestational diabetes.

To check whether women have diabetes, some doctors first take a sample of blood, usually after women have fasted overnight, and do a blood test to measure the blood sugar (glucose) level.

But the best way to confirm the diagnosis of diabetes is a two-part test that begins by having the woman drink a liquid that contains glucose. One hour after the woman drinks the liquid, doctors take and test samples of blood to determine whether the blood sugar level becomes abnormally high. If it is abnormally high, doctors give her a liquid that contains larger amount of glucose. After 3 hours, her blood sugar level is measured again. If it is still abnormally high, diabetes is diagnosed. This test is called the oral glucose tolerance test.

Treatment of Diabetes During Pregnancy

  • Close monitoring of the woman and fetus

  • Diet, exercise, and sometimes drugs to control the blood sugar level

  • A glucagon kit (to be used if blood sugar levels decrease too much)

  • Sometimes a drug to start labor

To reduce the risk of problems, doctors usually do the following:

  • Involve a diabetes team (including nurses, a nutritionist, and social workers) and a pediatrician.

  • Promptly diagnose and treat any pregnancy-related problems, no matter how trivial

  • Plan for delivery and have an experienced pediatrician present

  • Make sure that intensive care is available for the newborn (if needed)

Controlling blood sugar levels

The risk of complications during pregnancy can be reduced by controlling the level of sugar in the blood. The level should be kept as near normal as possible throughout pregnancy.

Doctors advise women who have diabetes and who are planning to become pregnant to immediately start taking steps to control their blood sugar level if they have not already done so. These steps include following an appropriate diet, exercising, and, if needed, taking insulin. High-sugar foods are eliminated from the diet, and women should eat so that they do not gain excess weight during pregnancy.

Most pregnant women with diabetes are asked to measure their blood sugar level several times a day at home using a home blood sugar monitoring device. If blood sugar levels are high, women may need to take an oral hypoglycemic drug or insulin.

Treatment sometimes causes blood sugar levels to decrease too much (called hypoglycemia). Hypoglycemia, if severe, causes confusion and loss of consciousness and can occur without any warning. If a woman is prone to episodes of hypoglycemia (for example, if she has had type 1 diabetes for a long time), she is given a glucagon kit and taught how to use it. Glucagon, when injected, increases blood sugar levels. A family member is also taught how to use the kit. Then if symptoms of severe hypoglycemia occur, the woman or the family member can inject glucagon.

Controlling diabetes is particularly important late in pregnancy because then, the blood sugar level tends to increase. A higher dose of insulin is usually needed.

Monitoring the fetus

Women are often asked to count the number of times they feel the fetus move each day. If all is well, they should feel at least 10 movements (kicks, flutters, or rolls) within 2 hours. Usually, the fetus moves 10 times in less time. Women should report any sudden decreases in movement to the doctor immediately.

Doctors monitor the fetus by doing tests such as fetal heart rate monitoring, nonstress tests, or biophysical profiles (using ultrasonography). Monitoring often begins at 32 weeks of pregnancy or sooner if complications develop—for example, if the fetus is not growing as much as expected or if the woman develops high blood pressure.

If any of the following are present, doctors may remove and analyze a sample of the fluid that surrounds the fetus (amniotic fluid):

  • Women have had pregnancy-related problems in previous pregnancies.

  • The due date is uncertain.

  • Blood sugar has not been well-controlled.

  • Care during the pregnancy has been inadequate.

  • Women are not following their treatment plan as directed.

This procedure, called amniocentesis, helps doctors determine whether the fetus’s lungs are mature enough to breathe air and thus determine when the baby can be delivered safely.

Labor and delivery

If labor has not started by 39 weeks, doctors may start labor using a drug (called induction of labor). If blood sugar is not controlled well or if women are not following their treatment plan, labor may be started as early as 37 weeks. Usually, vaginal delivery is possible.

During labor and delivery, many women with diabetes need to be given a continuous infusion of insulin through a catheter inserted in a vein.

After delivery

In newborns of women with diabetes, hospital staff members measure blood levels of sugar, calcium, and bilirubin because these newborns often have abnormal levels. The newborns are also observed for symptoms of these abnormalities.

For women with diabetes, the requirement for insulin dramatically drops immediately after delivery. But the requirement usually returns to what it was before pregnancy within about 1 week.

After delivery, gestational diabetes usually disappears. However, many women who have gestational diabetes develop type 2 diabetes as they become older.

Drugs Mentioned In This Article

Generic Name Select Brand Names
No US brand name
NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Test your knowledge

Abortion is defined as the intentional ending of a pregnancy by surgery or drugs. Which of the following statements about abortion in the United States is most accurate? 
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID