Health care providers consider labor to be preterm if it starts before 37 weeks of pregnancy. Because a fetus is not fully grown at 37 weeks, and it may not be able to survive outside the womb, health care providers will often take steps to stop labor if it starts before this time. Common methods for trying to stop labor include bed rest and medications that relax the muscles in the uterus involved with labor and delivery.
However, the American College of Obstetricians and Gynecologists (ACOG) recently reported that many of the methods used to stop preterm labor are ineffective. The ACOG announcement confirms NICHD-supported research, which found that home uterine monitors were not effective for predicting or preventing preterm labor.
If efforts to stop labor fail, then the baby could be born prematurely. Premature infants face a number of health challenges, including low birth weight, breathing problems, and underdeveloped organs and organ systems. Many infants that are born prematurely need to stay in the hospital until their health is stable, sometimes several weeks or more.
NICHD Research on Preterm Labor and Premature Birth
Despite attempts to stop labor, many cases of preterm labor end in premature birth. Premature birth occurs in between 8 percent to 10 percent of all pregnancies in the United States; it remains one of the top causes of infant death in this country. Infants who survive being born prematurely are at increased risk for certain life-long health effects, such as cerebral palsy, blindness, lung diseases, learning disabilities, and developmental disabilities.
Current NICHD-supported research is trying to identify markers and predictors of preterm labor and premature birth. In one study, researchers are investigating premature rupture of membranes (PROM), a situation in which the membranes that support the fetus in the womb break (sometimes referred to as "when a woman's water breaks") before the fetus is fully developed. PROM can lead to preterm labor and premature birth. Researchers found that, in some cases, the womb and the fetus produce enzymes, proteins that speed up certain chemical reactions, which can cause the membranes to break apart. Further research is now underway to figure out whether other features may make some women more likely to experience PROM. The findings of this research may lead to new methods of preventing PROM and some premature births.
Past research revealed that certain infections can make a woman more likely to experience preterm labor and give birth early. For instance, women who have bacterial vaginosis, the most common vaginal infection for women of reproductive age, are more likely than other women to experience preterm labor and give birth prematurely. Similarly, women who have trichomoniasis, a sexually transmitted infection, are also more likely to give birth prematurely than women who don't have the infection. It would stand to reason, then, that treating these infections would prevent premature births in these cases. But, NICHD-supported studies have shown that treating these infections is not an effective way to prevent premature birth. Further research is now underway to find other options for treating these infections that may reduce the risk of premature birth. For more information on this research, read the news release on the bacterial vaginosis and the news release on trichomoniasis.
One effective way to understand preterm labor and premature delivery is to study the characteristics of women who have given birth prematurely. One group of NICHD-supported researchers found that, among women who had given birth prematurely in the past, a shortened cervix could be a warning sign in preterm labor for a current pregnancy. With this knowledge, scientists can work to develop ways of preventing this shortening of the cervix, which may help to prevent preterm labor and premature delivery. For more information on this research, read the news release about shortened cervix and premature birth.
In addition, research on preterm labor and premature birth is ongoing through the NICHD's Maternal-Fetal Medicine Units (MFMU) Network, a research program that uses 14 sites around the country to conduct studies related to the mechanisms of pregnancy and birth. Researchers in the MFMU Network recently completed a clinical trial, which showed that the hormone progesterone may prevent repeated premature birth in a specific group of women, those who were carrying a single fetus, and who previously gave birth prematurely, between 20 and 26 weeks of pregnancy. In this trial, the progesterone treatment started between the 16th and 20th week of pregnancy, and continued through the 36th week of pregnancy. This finding may help to reduce future premature births among women who have a history of preterm labor and premature delivery.
NICHD-supported researchers were also working to see whether having more uterine contractions during pregnancy could be a warning sign of premature birth. Many pregnant women have uterine contractions throughout their pregnancies. These contractions are often mild and usually occur after the mid-way point of pregnancy. But, this research showed that, even though how often a woman had contractions was significantly related to premature birth, it wasn't an effective way to predict which mothers would give birth prematurely.
The NICHD and other NIH Institutes are currently conducting a number of clinical trials related to premature birth.
Infant Problems Related to Premature Birth
Babies that are born prematurely face a number of problems, including low birth weight, respiratory and breathing difficulties, and underdeveloped organs and organ systems. Some research also suggests that babies born prematurely are at higher risk for certain health problems as they get older. To find ways to minimize the impact of premature birth on the health of infants, the NICHD supports and conducts observational and interventional studies on these topics.
Low Birth Weight (LBW) and Very Low Birth Weight (VLBW)
LBW refers to any baby that weighs less than 2,500 grams (about 5 pounds, 8 ounces). VLBW describes an infant that weighs less than 1,500 grams (about 3 pounds, 5 ounces). LBW and VLBW infants are at higher risk than other infants for a variety of problems, including cerebral palsy, sepsis (a type of blood infection), chronic lung disease, and death. These infants are also at higher risk for hypothermia (high-poh-THERM-ee-uh), low body temperature, which can be dangerous.
Research is now underway to learn how to increase the level of nutrition for these infants, to improve their survival rates, and find out what, if any, long-term effects these conditions have on overall health.
The NICHD and other Institutes are currently conducting a number of clinical trials related to LBW and VLBW.
Respiratory Distress Syndrome (RDS)
In RDS, the baby has trouble breathing. RDS can result from various situations, such as:
- The baby's lungs aren't fully developed. Health care professionals can give these infants certain types of steroids, called corticosteroids (CORE-tick-oh-stair-oids), to help the lungs mature more quickly. These steroids may also lower the risk of brain injury. Sometimes, giving the lungs a little extra push in their development can help the baby breathe easier, which allows the infant to get stronger. Health care providers may also give corticosteroids to a woman who is at risk of delivering her baby before 34 weeks of pregnancy, to try to prevent the infant from developing RDS.
- The lungs are missing an important material. For the lungs to work properly, their lining has to be completely covered with a slick, soapy coating called surfactant. A growing fetus doesn't make enough surfactant to breathe outside of the womb until a certain point in development. Babies born prematurely have about 5 percent of the total surfactant that they need, which puts them at high risk for RDS. Through research conducted and supported by the NICHD, premature babies can now receive replacement surfactant to coat their lungs and allow for easier breathing. In some cases, getting replacement surfactant can prevent RDS from occurring at all; in other cases, the replacement surfactant saves the baby's lungs from long-term damage.
In addition to the treatments for these situations, premature infants may also benefit from being placed on a respirator, a machine that helps them breathe by inflating and deflating their lungs. Oxygen treatments or treatments using nitric oxide may also improve the breathing.
Quick GuideEarly Signs & Symptoms of Pregnancy
Through this and other NICHD-supported research into the problems faced by premature infants, survival rates for premature infants with RDS are nearly 95 percent. The NICHD and other Institutes are also conducting clinical trials related to RDS.
The NICHD is currently conducting and sponsoring a number of clinical trials
involving infants born prematurely. The Institute's
Neonatal Research Network,
established in 1986, strives to improve the care of and outcomes for infants,
especially LBW and VLBW infants. The Neonatal Research Network follows thousands
of infants, through its 16 clinical centers throughout the country, to conduct
clinical trials and observational studies for preventing and treating problems
related to pregnancy, premature birth, and the newborn period. The Institute's
Maternal-Fetal Medicine Unit Network also conducts clinical trials on these
topics. Among the trials currently underway are: the BEAM (Beneficial
Effects of Antenatal Magnesium Sulfate) trial, to try and
prevent cerebral palsy; and the FOX (Fetal pulse OXimetry) trial,
to learn more about the effects of cesarean delivery.
Source: National Institutes of Health (www.nih.gov)