Diabetes Mellitus & Pregnancy


Diabetes mellitus, a clinical syndrome characterized by deficiency of or insensitivity to insulin and exposure of organs to chronic hyperglycemia, is the most common medical complication of pregnancy. Over 3 million persons in the United States are sufficiently affected by diabetes mellitus to warrant treatment with insulin or oral hyperglycemics. Another 3 million are treated with diet alone in addition to a possible 4 or more million with varying degrees of asymptomatic glucose intolerance.

Preexisting diabetes (ie, diabetes diagnosed prior to pregnancy) affects approximately 1-3 pregnancies per 1000 births. In spite of the goal of preconception counseling for women with preexisting diabetes, many women will present for medical care for the first time during pregnancy. In this light, pregnancy affords a unique opportunity for diabetes screening and may well be the best opportunity in a woman's life to discover or prevent her diabetes.

Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with first recognition during pregnancy. GDM complicates approximately 4% of pregnancies (135,000 cases in the United States annually).

Hyperglycemia around the time of conception and early organogenesis results in the developing embryo having a 6-fold increase in midline birth defects. Ketoacidosis is an immediate threat to life and is the leading cause of perinatal morbidity in diabetic pregnancies today, accounting for 40% of perinatal mortality.

Complications of GDM include fetal macrosomia, which is associated with increased rates of secondary complications such as operative delivery, shoulder dystocia, and birth trauma. In addition, neonatal complications attributed to gestational diabetes include respiratory distress syndrome (RDS), hypocalcemia, hyperbilirubinemia, and hypoglycemia.

Before the introduction of insulin in 1922, patients often died during the course of their pregnancy. Twenty years ago it was not uncommon to deliver an unexplained stillbirth from a mother with type 1 diabetes mellitus. In an effort to prevent fetal death, deliveries were often performed early.

Today, this tragedy is rare, and over the last decade associated perinatal morbidity and mortality have been reduced from 60% to less than 5%. With therapy beginning prior to conception and continuing throughout pregnancy, including nutrition therapy, insulin when necessary, and eventual antepartum fetal surveillance, there is a marked decline in overall morbidity and mortality.

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    Diabetes Mellitus & Pregnancy

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    Two decades ago, most diabetics required prolonged hospitalization, but today the majority is managed with only brief hospitalizations. This is partly due to the technologic improvements in home reflectance glucose monitors and the beneficial impact they have had in management of the diabetic during pregnancy.

    Currently, the major challenges of caring for diabetics in pregnancy are first, to enhance preconceptual glucose control and reduce the risk of associated congenital malformations, second to adequately screen pregnant women, and third, to detail the full impact of milder glucose elevations, not only on maternal risk for developing diabetes, but also on immediate and long-term consequences to the fetus/child.

    What risks does pregestational diabetes pose to the baby?
    Poorly controlled pregestational diabetes poses a number of risks to the baby. These risks can be greatly reduced with good blood sugar control starting before pregnancy.

    • Birth defects: Women with poorly controlled diabetes in the early weeks of pregnancy are 3 to 4 times more likely than nondiabetic women to have a baby with a serious birth defect. These include heart defects or neural tube defects (NTDs), birth defects of the brain or spinal cord (1).
    • Miscarriage: High blood sugar levels around the time of conception may increase the risk of miscarriage (1).
    • Premature birth (before 37 completed weeks of pregnancy) (1): Premature babies are at increased risk of health problems in the newborn period as well as lasting disabilities.
    • Macrosomia: Women with poorly controlled diabetes are at increased risk of having a very large baby (10 pounds or more). Macrosomia is the medical term for this. These babies grow so large because some of the extra sugar in the mother's blood crosses the placenta and goes to the fetus. The fetus then produces extra insulin, which helps it process the sugar and store it as fat. The fat tends to accumulate around the shoulders and trunk, sometimes making these babies difficult to deliver vaginally and putting them at risk for injuries during delivery.
    • Stillbirth: Though stillbirth is rare, the risk is increased with poorly controlled diabetes (3).
    • Newborn complications: These include breathing problems, low blood sugar levels and jaundice (yellowing of the skin). These complications can be treated, but it's better to prevent them by controlling blood sugar levels during pregnancy.
    • Obesity and diabetes: Babies of women with poorly controlled diabetes may be at increased risk of developing obesity and diabetes as young adults (1).

    What risks does gestational diabetes pose to the baby?
    Babies of women with gestational diabetes usually face fewer risks than those of women with pregestational diabetes. Babies of women with gestational diabetes usually do not have an increased risk of birth defects (4). However, some women with gestational diabetes may have had unrecognized diabetes that began before pregnancy. These women may have had high blood sugar in the early weeks of pregnancy, which increases the risk of birth defects.

    Like pregestational diabetes, poorly controlled gestational diabetes increases the risk of macrosomia, stillbirth and newborn complications, as well as obesity and diabetes in young adulthood (5, 6).

    Does diabetes cause other pregnancy complications?
    Women with diabetes (pregestational and gestational) are likely to have an uncomplicated pregnancy and a healthy baby, as long as blood sugar levels are well controlled. However, women with poorly controlled diabetes are at increased risk of certain pregnancy complications. These include:

    • Preeclampsia: This disorder is characterized by high blood pressure and protein in the urine. Severe cases can cause seizures and other problems in the mother and poor growth and premature birth in the baby.
    • Polyhydramnios: Too much amniotic fluid (polyhydramnios) can increase the risk of preterm labor and delivery (1, 3).
    • Cesarean delivery: When the baby grows too large, a cesarean delivery often is recommended (5).

    What causes gestational diabetes?
    Gestational diabetes occurs when pregnancy hormones or other factors interfere with the body's ability to use its insulin. An affected woman usually has no symptoms. This form of diabetes usually develops during the second half of pregnancy and goes away after delivery.

    Who is at risk of gestational diabetes?
    Women with certain risk factors are more likely to develop gestational diabetes. These risk factors include (5, 7):

    • Had gestational diabetes in a previous pregnancy
    • Age over 30
    • Overweight and/or excessive weight gain during pregnancy
    • Had a very large (over 91/2 pounds) or stillborn baby in a previous pregnancy
    • African-American, Native American, Asian, Hispanic, Pacific Island ancestry

    However, even women who don't have any risk factors can develop gestational diabetes. For this reason, health care providers screen most pregnant women for the disorder. According to the American Diabetes Association (ADA), women under age 25 who have no other risk factors may not require screening because they have a very low risk of the disorder (8).

    What can a woman with diabetes do before pregnancy to reduce the risks to her baby?

    Women who have pregestational diabetes or who had gestational diabetes should consult their health care provider before attempting to conceive. Preconception care (care before getting pregnant) can help a woman get her blood-sugar levels under control before pregnancy. This is important because the birth defects associated with diabetes originate in the early weeks of pregnancy, before a woman may realize she is pregnant.

    At a preconception visit, women who are overweight should discuss with their provider how to reach a healthy weight before conceiving. Women who are overweight or obese are at increased risk for gestational diabetes and other pregnancy complications, including high blood pressure, premature birth, stillbirth and having a baby with certain birth defects (12). Women who have already had gestational diabetes may be able to reduce their risk in another pregnancy by reaching a healthy weight before their next pregnancy.

    Women who are obese or overweight should ask their provider about their pregnancy weight-gain goal. Generally, women who are overweight should gain 15 to 25 pounds, and women who are obese should gain 15 pounds (12).

    The provider may recommend that a woman with pregestational diabetes have a blood test that measures glycosylated hemoglobin (a substance formed when glucose in the blood attaches to the hemoglobin protein in red blood cells) every 1 to 2 months. This test shows how well blood sugar has been controlled during the past 2 to 3 months. It can help determine when it is safest to try to conceive. The test also may be used to monitor blood-sugar control during pregnancy. The provider may recommend that a woman who had gestational diabetes have a blood-sugar test to see if her blood-sugar levels have returned to normal, or whether she has developed diabetes.

    All women should take a multivitamin containing 400 micrograms of the B vitamin folic acid, as part of a healthy diet, starting at least 1 month before pregnancy, to help prevent NTDs. Women with pregestational diabetes are at increased risk of having a baby with an NTD, so taking folic acid may be especially important for them. In some cases, the provider may recommend that the woman take a larger dose (1). Daily doses of 4,000 micrograms have proven successful in reducing the risk of having another baby with an NTD in women who already have had an affected baby.

    At a preconception visit, the provider may recommend that women with pregestational diabetes who take oral diabetes medications switch to insulin.


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    Correa, A., et al. Diabetes Mellitus and Birth Defects. American Journal of Obstetrics and Gynecology, September 2008, volume 199:237.el-237.e9.
    American College of Obstetricians and Gynecologists (ACOG). Your Pregnancy and Birth, 4th edition. ACOG, Washington, DC, 2005.
    Centers for Disease Control and Prevention (CDC). Diabetes and Pregnancy: Frequently Asked Questions. Accessed 10/11/07.
    American College of Obstetricians and Gynecologists (ACOG). Gestational Diabetes. ACOG Practice Bulletin, number 30, September 2001.
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    Langer, O., et al. Insulin and Glyburide Therapy: Dosage, Severity Level of Gestational Diabetes, and Pregnancy Outcome. American Journal of Obstetrics and Gynecology, volume 192, January 2005, pages 134-139.
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    American Diabetes Association (ADA). Gestational Diabetes Mellitus. Diabetes Care, volume 27, supplement 1, January 2004, pages s88-s90.
    American College of Obstetricians and Gynecologists (ACOG). Obesity in Pregnancy. ACOG Committee Opinion, number 315, September 2005.