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Preterm Labor

By Julie S. Moldenhauer, MD

Labor that occurs before 37 weeks of pregnancy is considered preterm.

  • Measures such as rest and sometimes drugs may be used to delay labor.

  • Antibiotics, corticosteroids, or drugs that slow labor may be needed.

What causes preterm labor is not well understood. However, certain conditions may make it more likely:

  • Premature rupture of membranes

  • Previous preterm deliveries

  • Genital infections, including some sexually transmitted diseases

  • Infections of the kidneys or the membranes containing the fetus

  • Structural weakness of the cervix

  • Pregnancy with more than one fetus

  • Abnormalities in the placenta, uterus, or fetus

A healthy lifestyle during pregnancy can help reduce the risk of preterm labor, as can regular visits to the doctor or midwife, who can then identify potential problems early.

Because babies born prematurely can have serious health problems (see page Prematurity), doctors try to prevent or stop labor that begins before the 34th week of pregnancy. Preterm labor is difficult to stop. If vaginal bleeding occurs or the membranes rupture, allowing labor to continue is often best. If vaginal bleeding does not occur and the membranes are not leaking amniotic fluid (the fluid that surrounds the fetus in the uterus), the woman is advised to rest and to limit her activities as much as possible, preferably to sedentary ones. She is given fluids and may be given drugs that can slow labor. These measures can often delay labor for a brief time.

Samples may be taken from the cervix, vagina, and anus to culture. Analysis of these samples may suggest a specific infection as the cause of preterm labor.

Drugs that can slow labor include the following:

  • Magnesium sulfate: This drug is often given intravenously to stop preterm labor. However, if the dose is too high, it may affect the woman’s heart and breathing rates.

  • Calcium channel blockers: These drugs are usually used to treat high blood pressure. They sometimes cause headaches and low blood pressure in the woman.

  • Prostaglandin inhibitors: These drugs may transiently reduce the amount of amniotic fluid. They are not used after the 32nd week of pregnancy because they may cause heart problems in the fetus.

  • Terbutaline: Terbutaline, given by injection, is no longer commonly used to stop preterm labor. If it is used, it is stopped after 48 to 72 hours because using it longer can cause heart problems in the woman.

Women are given antibiotics until culture results are obtained. If results are negative, the antibiotics are then stopped.

If the cervix opens (dilates) more than 2 inches (5 centimeters), labor usually continues until the baby is born. If doctors think that premature delivery is inevitable, a woman may be given a corticosteroid such as betamethasone. The corticosteroid helps the fetus’s lungs and other organs mature more quickly and reduces the risk that after birth, the baby will have difficulty breathing (neonatal respiratory distress syndrome) or other problems related to prematurity.

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* This is the Consumer Version. *