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Preterm Labor

By Julie S. Moldenhauer, MD, Associate Professor of Clinical Obstetrics and Gynecology in Surgery, The Garbose Family Special Delivery Unit; Attending Physician, The Center for Fetal Diagnosis and Treatment, Children's Hospital of Philadelphia; The University of Pennsylvania Perelman School of Medicine

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

  • Babies born premature can have serious health problems.

  • The diagnosis of preterm labor is usually obvious.

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

  • Antibiotics or corticosteroids may also be needed.

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

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.

Babies born prematurely can have serious health problems (see Premature Newborn), such as bleeding in the brain. When there is bleeding in the brain, the brain may not develop normally, causing problems such as cerebral palsy. Thus, doctors try to prevent or stop labor that begins before the 34th week of pregnancy. Preterm labor is difficult to stop.


  • A doctor's evaluation

The diagnosis of preterm labor is usually obvious, based on the signs that labor is starting and the length of the pregnancy.

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.

A sample of urine may be analyzed and cultured to check for kidney and bladder infections.


  • Sometimes allowing labor to continue

  • If labor needs to be delayed, rest, fluids, drugs that slow labor, antibiotics, and sometimes corticosteroids

If vaginal bleeding occurs or the membranes around the fetus 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.

Drugs that can slow labor include the following:

  • Magnesium sulfate: This drug is often given intravenously to stop preterm labor, particularly if the pregnancy is less than 32 weeks. Magnesium sulfate also appears to substantially reduce the risk of bleeding in the brain and problems with development of the newborn's brain, such as cerebral palsy. 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.

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. It also reduces the risk that after birth, the baby will have difficulty breathing (neonatal respiratory distress syndrome) or other problems related to prematurity.