Preterm Labor and Birth

Preterm labor (also called premature labor) is labor that begins before 37 weeks of pregnancy. Because the fetus is not fully grown at this time, it may not be able to survive outside the womb. Health care providers will often take steps to try to stop labor if it occurs before this time.

Signs and Symptoms

The signs of preterm labor include:

• Contractions (the uterus tightens and feels hard) every 10 minutes or more frequently
• Low, dull backache, especially if it comes and goes
• Change in vaginal discharge (leaking fluid or blood from the vagina)
• Pelvic pressure—the feeling that the baby is pushing down
• Cramps similar to those felt during a woman's period
• Abdominal cramps with or without diarrhea

Causes

The causes of preterm labor are often difficult to identify. However, some of the reasons for preterm labor can be put into four general categories:

1. Placental problems: Placenta praevia and placental abruption can cause bleeding behind the placenta and can lead to preterm labor and premature rupture of fetal membranes (the bag of water breaks too early).
2. The uterus is stretched too much, which often results from multiple babies (twins, triplets, etc) or from too much amniotic fluid (polyhydramnios)
3. Inflammation caused by an infection can cause contractions.
4. Severe stress: Both physical and psychological stress leads the body to release stress hormones which can cause uterine contractions.

Diagnosis

In women without symptoms but who are at high risk for delivering early, several tests are available including:

• Monitoring uterine contractions on a non-stress test
• Measuring the length of the cervix by ultrasound
• Testing for fetal fibronectin (protein)
• Doing a vaginal exam to see if the cervix has dilated (started to open)

Non-stress test

Monitors are placed on the pregnant woman’s abdomen. They record the fetal heart rate and frequency of contractions.

Cervical ultrasound

Some physicians will check the length of the cervix using an ultrasound machine with a vaginal probe. If the cervix is shorter than normal or if the inside part of the cervix is starting to open (the cervix starts to look like a funnel), then the woman is placed on bed rest and is monitored for contractions.

Fetal Fibronectin (fFN)

Fetal fibronectin (also known as fFN) is a “glue-like” protein that holds the baby in place in the uterus (womb). This protein is normally found in vaginal secretions at the very beginning of pregnancy and then again after 35 weeks of pregnancy.

A woman’s health care provider can test for the fetal fibronectin protein in vaginal secretions between 24 and 34 weeks of gestation in women who are at high risk for premature delivery. Normally this protein is not found in vaginal secretions during that time. If the fetal fibronectin protein test comes back negative, the patient has a 99% chance that she will not deliver in the next two weeks. This test can therefore be reassuring for women who are at higher risk for early delivery (such as women who are carrying twins.)

Treatment

Treatment includes:

• Identifying women who are at high risk for premature delivery and monitoring them closely throughout pregnancy
• Teaching all patients about preterm labor symptoms
• Progesterone to help prevent preterm labor in high risk women
• Use of tocolytic ("contraction-breaking") medications to relax the uterus and stop preterm contractions
• Use of corticosteroid medicines to help mature the baby’s lungs
• Bedrest
• Antibiotics to treat infections if suspected, and especially if the woman has preterm premature rupture of membranes

Recognizing the symptoms of preterm labor is key to preventing preterm delivery. If a woman feels that she is having regular cramping, is leaking amniotic fluid, or is having vaginal bleeding, she should call her doctor right away.

Medications (called tocolytics) can be given to slow or stop labor if they are given early enough. The tocolytics relax the uterine muscles. Common tocolytic medications are terbutaline, magnesium sulfate, nifedipine, and indomethacin.

The goal of these medications is to allow time for corticosteroids (such as betamethasone or dexamethasone) to be given. If these steroids are given at least 24 to 48 hours before birth, they can help the baby’s lungs to mature. They also help to prevent bleeding in the premature baby’s brain.

Recent studies have shown that treating high-risk pregnant women (those who have previously had a premature baby) with a form of the hormone progesterone reduces the risk of another preterm delivery. The treatment worked among all ethnic groups in the study and improved outcomes for the babies. Studies to find out whether the treatment works for other at-risk women, such as those having twins and triplets, are ongoing.

In addition to tocolytic medications, bed rest can reduce the pressure of the baby on the cervix which can help reduce the dilation of the cervix in some cases.

Prevention

Research supported by the NICHD found that treating high-risk pregnant women (those who have previously had a spontaneous preterm baby) with a certain type of progesterone reduces the risk of another preterm delivery. The treatment worked among all ethnic groups in the study and improved outcomes for the babies. Efforts to find out whether the treatment works for other at-risk women, such as those having twins and triplets, are ongoing.

Bed rest and medications that relax the muscles in the uterus are also commonly used to try to stop preterm labor.

Chances of Developing Preterm Labor and Birth

A baby born before 37 weeks of pregnancy is considered a preterm birth (or premature birth). Preterm births occur in about 12 percent of all pregnancies in the U.S. It is one of the top causes of infant death in this country.

Eighty percent of preterm births happen because of preterm labor or premature rupture of the fetal membranes (or "broken bag of waters"). The other 20 percent are planned early deliveries that are done for maternal or fetal safety reasons.

About 60 percent of women who have preterm labor will deliver their baby prematurely. Early intervention including testing, medications to stop labor and bed rest can help the other 40 percent of women with preterm labor to go on to deliver at term.

Risk factors

Health care providers currently have no way of knowing which women will experience preterm labor or deliver their babies preterm, but there are factors that place a woman at higher risk for preterm labor or birth:

• Certain infections, such as bacterial vaginosis and trichomoniasis
• Shortened cervix
• Previously preterm deliveries

In addition, some studies have shown that the following may put a pregnant woman at an increased risk for preterm labor:

• Urinary tract infections (bladder infection)
• Vaginal infections (including bacterial vaginosis and trichomoniasis)
• Diabetes
• Too much amniotic fluid (polyhydramnios)
• Clotting problems (thrombophilias)
• Short amount of time between pregnancies (less than 6 months between birth and the beginning of the next pregnancy)
• Smoking or using illegal drugs such as cocaine
• Late or no prenatal care
• Domestic violence
• Long working hours which require standing for long periods of time

Related Problems

Premature infants may face a number of health challenges, including:

• Low birth weight
• Breathing problems because of underdeveloped lungs
• Underdeveloped organs or organ systems
• Greater risk for life-threatening infections
• Greater risk for a serious lung condition, known as respiratory distress syndrome
• Greater risk for cerebral palsy (CP)
• Greater risk for learning and developmental disabilities

Babies born prematurely may need to stay in the hospital for several weeks or more, often in a neonatal intensive care unit (NICU).

Research

Researchers have found that other methods of stopping preterm labor are not as effective as once thought. For instance, NICHD-supported researchers have found that uterine monitors are not effective for predicting or preventing preterm labor.

In addition, NICHD-funded research found that screening women who do not show any symptoms of infection, but who have vaginosis and received treatment with antibiotics, did not prevent preterm birth.

References

Alfirevic Z, Allen-Coward H, Molina F, Vinuesa CP, Nicolaides K. Targeted therapy for threatened preterm labor based on sonographic measurement of the cervical length: a randomized controlled trial. Ultrasound Obstet Gynecol. 2007 Jan;29(1):47-50. PMID: 17201013

Crowley PA. Antenatal corticosteroid therapy: a meta-analysis of the randomized trials, 1972 to 1994. Am J Obstet Gynecol. Jul 1995;173(1):322-35. PMID: 7631713

Dodd JM, Flenady VJ, Cincotta R, Crowther CA. Progesterone for the prevention of preterm birth: a systematic review. Obstet Gynecol. 2008 Jul;112(1):127-34. PMID: 18591318

Fox NS, Gelber SE, Kalish RB, Chasen ST. Contemporary practice patterns and beliefs regarding tocolysis among u.s. Maternal-fetal medicine specialists. Obstet Gynecol. 2008 Jul;112(1):42-7. PMID: 18591306

Goldenberg RL, Iams JD, Mercer BM, et al. The preterm prediction study: the value of new vs. standard risk factors in predicting early and all spontaneous preterm births. Am J Public Health. 1998; 88:233-238 PMID: 9491013

Goldenberg RL, Culhane JF, Iams JD, Romero R. Epidemiology and causes of preterm birth. Lancet. 2008 Jan 5;371(9606):75-84. Review. PMID: 18177778

Morgan MA, Goldenberg RL, Schulkin J. Obstetrician-gynecologists' screening and management of preterm birth. Obstet Gynecol. 2008 Jul;112(1):35-41. PMID: 18591305

Moster D, Lie RT, Markestad T. Long-term medical and social consequences of preterm birth. N Engl J Med. 2008 Jul 17;359(3):262-73. PMID: 18635431

Tanir HM, Sener T, Yildiz Z. Cervicovaginal fetal fibronectin (FFN) for prediction of preterm delivery in symptomatic cases: a prospective study. Clin Exp Obstet Gynecol. 2008;35(1):61-4. PMID: 18390084

External Links

• National Library of Medicine: [www.nlm.nih.gov/medlineplus/healthtopics.html/ Preterm labor]

• National Institute of Child Health and Human Development: womenshealth

• March of Dimes: Preterm Labor

• What Is Fetal Fibronectin (fFN)?

• American College of Obstetricians and Gynecologists Preterm Labor