What is preterm labor?

What is magnesium sulfate?


What is preterm labor?

Preterm labor is defined as regular contractions of the uterus resulting in changes in the cervix that start before 37 weeks of pregnancy. Changes in the cervix include effacement (the cervix thins out) and dilation (the cervix opens so that the fetus can enter the birth canal). In some cases preterm labor can lead to a baby being born too soon.


What is preterm birth?

When birth occurs between 20 weeks of pregnancy and 37 weeks of pregnancy, it is called preterm birth.


Why is preterm birth a concern?

Preterm birth is a concern because babies who are born too early may not be fully developed. They may be born with serious health problems. Some health problems, like cerebral palsy, can last a lifetime. Other problems, such as learning disabilities, may appear later in childhood or even in adulthood.


Which preterm babies are at greatest risk of health problems?

The risk of health problems is greatest for babies born before 34 weeks of pregnancy. But babies born between 34 weeks of pregnancy and 37 weeks of pregnancy also are at risk.


What are risk factors for preterm birth?

Factors that increase the risk of preterm birth include the following:

  • Having a previous preterm birth
  • Having a short cervix
  • Short time between pregnancies
  • History of certain types of surgery on the uterus or cervix
  • Certain pregnancy complications, such as multiple pregnancy and vaginal bleeding
  • Lifestyle factors such as low prepregnancy weight, smoking during pregnancy, and substance abuse during pregnancy


Can anything be done to prevent preterm birth if I am at high risk?

If you have had a prior preterm birth and you are planning another pregnancy, a prepregnancy care checkup can help you get in the best possible health before you become pregnant. When you become pregnant, be sure to start prenatal care early. You may be referred to a health care professional who has expertise in managing high-risk pregnancies. In addition, you may be given certain medications or other treatment to help prevent preterm birth if you have risk factors. Treatment is given based on your individual situation and your risk factors for preterm birth.


What are the signs and symptoms of preterm labor and what should I do if I have any of them?

Call your obstetrician or other health care professional right away if you notice any of these signs or symptoms:

  • Change in type of vaginal discharge (watery, mucus, or bloody)
  • Increase in amount of discharge
  • Pelvic or lower abdominal pressure
  • Constant low, dull backache
  • Mild abdominal cramps, with or without diarrhea
  • Regular or frequent contractions or uterine tightening, often painless
  • Ruptured membranes (your water breaks with a gush or a trickle of fluid)


How is preterm labor diagnosed?

Preterm labor can be diagnosed only when changes in the cervix are found. Your obstetrician or other health care professional may perform a pelvic exam to see if your cervix has started to change. You may need to be examined several times over a period of a few hours. Your contractions also may be monitored.

Your obstetrician or other health care professional may do certain tests to determine whether you need to be hospitalized or if you need immediate specialized care. A transvaginal ultrasound exam may be done to measure the length of your cervix. The level of a protein called fetal fibronectin in the vaginal discharge may be measured. The presence of this protein is linked to preterm birth.


If I have preterm labor, will I have a preterm birth?

It is difficult for health care professionals to predict which women with preterm labor will go on to have preterm birth. Only about 1 in 10 women with preterm labor will give birth within the next 7 days. For about 3 in 10 women, preterm labor stops on its own


What happens if my preterm labor continues?

If your preterm labor continues, how it is managed is based on what is thought to be best for your health and your fetus’s health. When there is a chance that the fetus would benefit from a delay in delivery, certain medications may be given. These medications include corticosteroids, magnesium sulfate, and tocolytics.


What are corticosteroids?

Corticosteroids are drugs that cross the placenta and help speed up development of the fetus’s lungs, brain, and digestive organs. Corticosteroids are most likely to help your fetus when they are given between 24 weeks of pregnancy and 34 weeks of pregnancy. They also may be given between 23 and 24 weeks of pregnancy.


What is magnesium sulfate?

Magnesium sulfate is a medication that may be given if you are less than 32 weeks pregnant, are in preterm labor, and are at risk of delivery within the next 24 hours. This medication may help reduce the risk of cerebral palsy that is associated with early preterm birth.


What are tocolytics?

Tocolytics are drugs used to delay delivery for a short time (up to 48 hours). They may allow time for corticosteroids or magnesium sulfate to be given or for you to be transferred to a hospital that offers specialized care for preterm infants. In addition to its role in protecting against cerebral palsy, magnesium sulfate also can be used as a tocolytic drug.


What happens if my labor does not stop?

If your labor does not stop and it looks like you will give birth to your baby early, you and the baby usually will be cared for by a team of health care professionals. The team may include a neonatologist, a doctor who specializes in treating problems in newborns. The care your baby needs depends on how early he or she is born. High-level neonatal intensive care units (NICUs) provide this specialized care for preterm infants.



Cerebral Palsy: A disorder of the nervous system that affects movement, posture, and coordination. This disorder is present at birth.

Cervix: The lower, narrow end of the uterus at the top of the vagina.

Corticosteroids: Drugs given for arthritis or other medical conditions. These drugs also are given to help fetal lungs mature before birth.

Fetal Fibronectin: A protein that is produced by fetal cells. It helps the amniotic sac stay connected to the lining of the uterus.

Fetus: The stage of human development beyond 8 completed weeks after fertilization.

Magnesium Sulfate: A drug that may help prevent cerebral palsy when it is given to women in preterm labor who may deliver before 32 weeks of pregnancy.

Neonatologist: A doctor who specializes in the diagnosis and treatment of disorders that affect newborn infants.

Obstetrician: A doctor who cares for women during pregnancy and their labor.

Pelvic Exam: A physical examination of a woman’s pelvic organs.

Placenta: An organ that provides nutrients to and takes waste away from the fetus.

Prenatal Care: A program of care for a pregnant woman before the birth of her baby.

Tocolytics: Drugs used to slow contractions of the uterus.

Transvaginal Ultrasound Exam: A type of ultrasound in which the device is placed in your vagina.

Uterus: A muscular organ in the female pelvis. During pregnancy, this organ holds and nourishes the fetus.

If you have further questions, contact your obstetrician–gynecologist.

FAQ087. Copyright January 2019 by the American College of Obstetricians and Gynecologists

This information is designed as an educational aid to patients and sets forth current information and opinions related to women’s health. It is not intended as a statement of the standard of care, nor does it comprise all proper treatments or methods of care. It is not a substitute for a treating clinician’s independent professional judgment. Read ACOG’s complete disclaimer.