Patient information: Gestational diabetes mellitus

GESTATIONAL DIABETES OVERVIEW

Gestational diabetes mellitus (GDM) is a condition that develops during pregnancy, when the body is not able to make enough insulin to overcome the body's resistance to insulin. The lack of insulin causes the woman's blood glucose (also called blood sugar) level to become elevated compared to the usual levels seen during pregnancy. Gestational diabetes affects between 3 and 5 percent of women during pregnancy.

Gestational diabetes is caused by hormones that are released by the placenta; the hormones require the body to make additional insulin. However, in women with GDM, the pancreas cannot produce an adequate amount of insulin.

It is important to recognize and treat gestational diabetes promptly to minimize the risk of complications in the baby. In addition, it is important for women with a history of GDM to be screened for diabetes after pregnancy due to an increased risk of developing type 2 diabetes in the years following delivery.

GESTATIONAL DIABETES RISK FACTORS

Women with any of the following characteristics are at increased risk of being diagnosed with gestational diabetes, compared to women without any of these characteristics:

• History of gestational diabetes in previous pregnancies
• A family history of diabetes, especially in first degree relatives (eg, parent, sibling)
• Being overweight
• Age greater than 25 years
• Previous delivery of a baby greater than nine pounds [4.1 kg]
• Personal history of abnormal glucose tolerance (sometimes called "pre-diabetes")
• Member of certain ethnic groups (in the United States: African-American, Latino, Native American, and Asian women)
• Previous unexplained stillbirth or birth of a malformed child
• If the woman herself weighed more than nine pounds [4.1 kg] or less than six pounds [2.7 kg] at birth
• Having glucose in the urine at the first prenatal visit
• Polycystic ovary syndrome (see "Patient information: Polycystic ovary syndrome (PCOS)")
• Current use of steroids (eg, prednisone)
• Current or pregnancy-related high blood pressure
• Rapid weight gain in the first half of pregnancy

GESTATIONAL DIABETES TESTING

There are differing opinions about the need to screen pregnant women for gestational diabetes; some groups recommend that all pregnant women undergo testing while others recommend that only pregnant women with risk factors be tested.

We recommend that all pregnant women be screened for gestational diabetes because identifying and treating gestational diabetes can reduce the risk of pregnancy complications.

Complications of gestational diabetes can include having a large baby (often defined as a birth weight greater than 9 lbs [4.1 kg]), injury to the mother/infant during delivery as a result of the large size of the baby, preeclampsia, and an increased chance of needing a cesarean delivery [1,2].

Timing of test — Screening for gestational diabetes is usually performed between 24 and 28 weeks of pregnancy. However, screening may be done earlier in the pregnancy if the clinician suspects that the woman has gestational diabetes because of risk factors such as a history of gestational diabetes in previous pregnancies, obesity prior to pregnancy (defined as a body mass index greater than 30, (calculator 1), glucose in the urine, or a strong family history of diabetes.

Test procedure — On the day of the screening test, the woman may eat and drink normally. She will be given 50 grams of glucose, usually in the form of a specially formulated orange or cola drink; this should be consumed within a few minutes. One hour later, a small sample of blood is drawn to measure the woman's blood glucose level.

Test results — If the woman's blood glucose is elevated, further testing is needed to determine with certainty if she has gestational diabetes (see 'Further testing' below. Clinicians vary in their definition of elevated blood glucose; most consider a value greater than130 to 140 mg/dL (7.2 to 7.7 mmol/L) to be "elevated". The one hour glucose test is a screening test, meaning that not everyone who has an elevated one hour blood glucose level will have gestational diabetes.

However, if the one hour blood glucose level is very high (≥200 mg/dL [11.1 mmol/L]), many clinicians do not perform any further testing because there is a very good chance that the woman has gestational diabetes.

Further testing — The three hour (or two hour, in some locations) oral glucose tolerance test (GTT) is used to determine with certainty if a woman has gestational diabetes. The test is done by measuring the woman's blood glucose level before she eats anything in the morning (fasting), then again one, two, and three hours after she drinks a glucose drink that contains 100 grams of glucose (twice the amount in the one hour test). Similar to the one hour test, this is usually in the form of a specially formulated orange or cola drink.

A woman is said to have gestational diabetes if two or more of her blood glucose values are above the following levels:

• Fasting: >95 mg/dL (5.3 mmol/L)
• One-hour: >180 mg/dL (10 mmol/L)
• Two-hour: >155 mg/dL (8.6 mmol/L)
• Three-hour: >140 mg/dL (7.8 mmol/L)

GESTATIONAL DIABETES TREATMENT

Women who are diagnosed with gestational diabetes are usually managed with a combination of dietary changes, home blood glucose monitoring, and in some cases, daily injections of insulin. Less commonly, an oral diabetes medication is used.

The goal of treatment for gestational diabetes is to reduce the risk that the baby will develop macrosomia (weigh greater than 9 lbs at birth). Macrosomia can make it difficult for the infant to pass through the pelvis (shoulder dystocia), which increases the risk of birth trauma to the infant (eg, fractured bones or nerve injury). A large baby is also more likely to cause injury to the soft tissues of woman's pelvis during the delivery and increases the risk that the woman will require a cesarean delivery. (See "Patient information: Cesarean delivery".)

Macrosomia is more likely if a woman's blood glucose levels are above normal during pregnancy. Normal blood glucose levels are as follows:

• Fasting: <90 mg/dL (5 mmol/L)
• One hour after a meal: <120 mg/dL (6.6 mmol/L)

Changes in diet — Women with gestational diabetes are usually encouraged to meet with a registered dietitian to determine approximately how many calories she should consume and how calories should be distributed throughout the day.

The number of calories recommended depends upon the woman's current and prepregnancy weight. The following are some general dietary recommendations:

• Avoid high calorie snacks and desserts, including soda, fruit punch, candy, chips, cookies, cakes, and full-fat ice cream.
• There is no evidence that use of artificial sweeteners such as aspartame (Nutrasweet®), sucralose (Splenda®), stevioside (Stevia®), or saccharin (Sweet 'N Low®) during pregnancy increases the risk of birth defects. One study in rats showed an increased risk of bladder cancer in offspring of pregnant rats that consumed very high doses of saccharin, while the only other study did not show an increased risk. Since there are alternatives to saccharin, some clinicians recommend avoiding it in pregnancy. There is no information on the safety of acesulfame potassium (Sunnet®) in pregnancy.
• Eat a lot of vegetables and fruits, at least five servings a day. Some fruits (eg, grapes, dried fruit) can increase the blood glucose level significantly and should be eaten in limited amounts. Limit starchy vegetables (eg, potatoes) but eat as many non-starchy fruits or vegetables as desired.
• Choose foods with whole grains rather than processed grains. Consider whole wheat bread, brown rice, or whole wheat pasta instead of white bread, white rice, or regular pasta.
• Eat a limited amount of red meat, and choose lean cuts of meat that end in loin (eg, pork loin, tenderloin, sirloin). Remove skin from chicken and turkey before eating.
• Choose low or fat-free dairy products, such as skim milk, non-fat yogurt, and low-fat cheese.
• Use liquid oils (olive, canola) instead of solid fats (butter, margarine, shortening) for cooking.

Blood glucose monitoring — Women with gestational diabetes are taught to check their blood glucose level and record the results (graph 1). Instructions for choosing a blood glucose meter, checking blood glucose levels at home, and methods to record the data are available separately. (See "Patient information: Self-blood glucose monitoring in diabetes mellitus".)

Initially, most women are advised to check their blood glucose level four times per day: before eating in the morning, and one hour after breakfast, lunch, and dinner. This information can help to determine if the blood glucose levels are on target (less than 90 mg/dL [5 mmol/L] before breakfast, less than 120 mg/dL [6.7 mmol/L] after meals). If glucose levels are consistently elevated, treatment with insulin is usually recommended. (See 'Insulin' below.)

If, however, blood glucose levels are consistently normal, the frequency of testing can sometimes be decreased. This should be discussed with the obstetrical provider on a regular basis because the need for testing can change through the course of pregnancy. For example, some women's blood glucose levels are initially controlled with diet alone, but later require treatment with insulin.

Exercise — Although exercise is not a necessary component of treatment of gestational diabetes, it may help to control blood glucose levels. Pregnant women who already exercise are encouraged to continue after being diagnosed with gestational diabetes. Women who did not previously exercise should talk to their obstetrical provider to determine if exercise is recommended, most women who do not have medical or pregnancy-related complications are able to exercise, at least moderately, throughout their pregnancy.

Insulin — Approximately 15 percent of women with gestational diabetes will require insulin because their blood glucose levels remain elevated despite changes in diet. Insulin is a medication that helps to reduce blood glucose levels and can reduce the risk of gestational diabetes-related complications, especially macrosomia.

Insulin must be given by injection because it is not effective when it is taken by mouth. Oral diabetes medications, such as those taken by people with type 2 diabetes, are not currently recommended during pregnancy in the United States. There is not enough data to determine whether these medications are as safe and effective as insulin. Studies are currently underway to clarify these concerns.

The dose and frequency of insulin injections that a woman will need depends upon her blood glucose levels, although most women start with a once daily injection at bedtime. If post-meal blood glucose levels remain elevated, more frequent insulin injections are usually recommended. Instructions for drawing up and injecting insulin are available separately. (See "Patient information: Diabetes mellitus type 2: Insulin treatment".)

Women who require insulin are strongly encouraged to check their blood glucose level at least four times per day, record these values, and review them at each prenatal visit (graph 1). Maintaining accurate records helps to adjust insulin doses and can decrease the risk of complications.

MONITORING DURING PREGNANCY

Prenatal visits — Most women who develop gestational diabetes have more frequent prenatal visits (eg, once per week or two), especially if insulin is used. The purpose of these visits is to monitor the health of the woman and her infant, discuss her diet, and adjust the dose of insulin to optimize blood glucose levels. It is common to change the dose of insulin as the pregnancy progresses.

Nonstress testing — Tests that monitor the health of the baby may be recommended during the last trimester of pregnancy, especially for women with persistently elevated blood glucose levels, those who require insulin, and those who have other pregnancy-related complications (eg, high blood pressure). The most commonly used test is the nonstress test. This test is discussed in a separate topic review. (See "Patient information: Postterm pregnancy".)

LABOR AND DELIVERY WITH GESTATIONAL DIABETES

If blood glucose levels are close to normal during pregnancy and there are no other complications, the ideal time to deliver is at term or between 39 and 40 weeks of pregnancy. If a woman does not deliver by her due date, additional testing may be recommended to monitor the health of the woman and her baby. (See "Patient information: Postterm pregnancy".)

In most women with a normal size baby, there are no advantages of a cesarean delivery over a vaginal delivery. The risks and benefits of cesarean delivery are discussed separately. (See "Patient information: Cesarean delivery".)

Blood glucose levels will be monitored during labor because high blood glucose levels during labor can cause problems in the baby both before and after delivery. Insulin is not usually required unless the woman's blood glucose level becomes elevated (above 90 mg/dL or 5 mmol/L).

AFTER DELIVERY CARE

After delivery, most women with gestational diabetes have normal blood glucose levels and do not require further treatment with insulin. Women can resume their usual diet and are encouraged to breastfeed. (See "Patient information: Deciding to breastfeed".)

However, it is important to check the blood glucose level the day after delivery to confirm that the blood glucose level is normal or near normal. Pregnancy itself does not increase the risk of developing type 2 diabetes. However, the presence of gestational diabetes indicates that the woman has a greatly increased risk of developing type 2 diabetes later in life.

Some providers also recommend that women with gestational diabetes test their blood glucose level intermittently during the first few weeks after delivery. If any level is elevated (>100 mg/dL [5.6 mmol/L] before breakfast or >140 mg/dL [7.8 mmol/L] two hours after a meal), the woman should notify her healthcare provider.

If the woman's blood glucose level is normal after delivery, testing for type 2 diabetes is recommended at six weeks postpartum. Testing usually includes a two hour glucose tolerance test (GTT).

Risk of gestational diabetes — One-third to two-thirds of women who have gestational diabetes in one pregnancy will have it again in a subsequent pregnancy.

Risk of type 2 diabetes — Women with gestational diabetes have an increased risk of developing type 2 diabetes later in life, especially if the woman has other risk factors (eg, obesity, family history of type 2 diabetes). The greatest increase in risk occurs within the first five years after the pregnancy.

The risk of developing type 2 diabetes is greatly affected by body weight. Women who are obese have a 50 to 75 percent risk of type 2 diabetes while women who are normal weight have a less than 25 percent risk. Women who are overweight or obese are also encouraged to lose weight and to exercise regularly.

The American Diabetes Association recommends that all women with a history of gestational diabetes undergo testing for type 2 diabetes at least every three years after their pregnancy; women who have gestational diabetes after age 45 should have testing once per year. Testing is usually done by measuring the blood glucose level while fasting (eg, before breakfast).

Birth control — Women with a history of gestational diabetes can use any type of birth control after pregnancy. The optimal choice depends upon the woman's personal preferences, medical history, plans for future children, and whether or not she is breastfeeding. A review of all of the birth control options is available separately. (See "Patient information: Birth control; which method is right for me?".)

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Polycystic ovary syndrome (PCOS)
Patient information: Cesarean delivery
Patient information: Self-blood glucose monitoring in diabetes mellitus
Patient information: Diabetes mellitus type 2: Insulin treatment
Patient information: Postterm pregnancy
Patient information: Deciding to breastfeed
Patient information: Birth control; which method is right for me?

Professional Level Information:
Diagnosis of diabetes mellitus
Effect of advanced age on fertility and pregnancy in women
Infant of a diabetic mother
Obstetrical management of pregnancy complicated by pregestational diabetes mellitus
Screening and diagnosis of gestational diabetes mellitus
Treatment and course of gestational diabetes mellitus

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/ency/article/000896.htm, available in Spanish)

• National Institute of Diabetes and Digestive and Kidney Diseases

      (http://diabetes.niddk.nih.gov/dm/pubs/gestational/)

• American Diabetes Association (ADA)

      (800)-DIABETES (800-342-2383)
      (www.diabetes.org/gestational-diabetes.jsp)

• The Hormone Foundation

      (www.hormone.org/public/diabetes.cfm, available in English and Spanish)

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