Preterm Birth
Most pregnancies last around 40 weeks. Babies born between 37 and 42 weeks of pregnancy are called full term. Babies born before 37 completed weeks of pregnancy are called premature or preterm. About 12 percent of babies in the United States are born preterm. Of those, the majority (84 percent) are born between 32 and 36 weeks of gestation. About 10 percent are born between 28 and 31 weeks of gestation, and about 6 percent are born at less than 28 weeks of gestation.
All babies born preterm are at risk for serious health problems, but those born earliest are at greater risk of medical complications, long-term disabilities and death. Fortunately, advances in obstetrics and neonatology, the branch of pediatrics that deals with newborns, have improved the chances for survival for even these smallest babies.
Babies born preterm face a greater risk of serious health problems for several reasons. The earlier a child is born, the less she will weigh, the less developed her organs will be, and the more complications she is likely to face. These babies may require care in a neonatal intensive care unit (NICU), which has specialized medical staff and equipment that can deal with the multiple problems faced by premature infants. Very premature babies also have the highest risk of death and lasting disabilities, such as mental retardation, cerebral palsy, lung and gastrointestinal problems, and vision and hearing loss.
Not only are premature babies often small and sick, but they may look and behave very differently than full-term babies. For example, their skin may be thin and wrinkled, and their heads may look too large for their bodies. But these babies look the way they should at their stage of development, and will begin to appear and act more like full-term babies as they continue to develop and grow. Throughout their first year of life, these babies should be evaluated according to their adjusted age (which takes their prematurity into account).
What causes preterm birth?
A baby may be delivered preterm after a doctor induces labor due to pregnancy complications or health problems in the mother. However, most preterm births are a result of spontaneous preterm labor (which may follow spontaneous premature rupture of the membranes or PROM—the sac inside the uterus that holds the baby breaks too soon). The causes of preterm labor and PROM are not fully understood, but the latest research suggests that many cases are triggered by the body’s natural response to certain infections, including infections involving the amniotic fluid and fetal membranes. However, in nearly half of all cases, the doctor cannot determine why a woman delivered preterm. And, at this time, there often is little the doctor or the pregnant woman can do to prevent preterm labor.
Which women are at increased risk of preterm delivery?
Any woman can deliver prematurely, but some women are at greater risk than others. Researchers have identified some risk factors, but experts still can’t predict which women will delivery prematurely.
Studies show that a woman is at high risk of preterm birth if she:
- Has had a previous preterm birth
- Is pregnant with twins, triplets or more
- Has certain uterine or cervical abnormalities
Researchers also have identified other risk factors. For instance, African-American women, women younger than 17 or older than 35, and poor women are at greater risk than other women. Certain lifestyle and environmental factors may put a woman at greater risk of preterm labor. These include: late or no prenatal care, smoking, drinking alcohol, using illegal drugs, exposure to the medication diethylstilbestrol (DES), domestic violence (including physical, sexual or emotional abuse), lack of social support, stress, and long working hours with long periods of standing.
Certain medical conditions during pregnancy also may increase the likelihood that a woman will have preterm labor. These include: infections (including urinary tract, vaginal, sexually transmitted and possibly other infections), diabetes, high blood pressure, clotting disorders (thrombophilia), bleeding from the vagina, certain birth defects in the baby, being pregnant with a single fetus after in vitro fertilization (IVF), being underweight before pregnancy, obesity, and short time period between pregnancies (less than 6-9 months between birth and the beginning of the next pregnancy).
How can a woman reduce her risk of preterm delivery?
A woman may be able to reduce her risk of preterm delivery by visiting her health care provider before pregnancy and, once pregnant, seeking early and regular prenatal care. A pre-pregnancy visit is especially crucial for women with chronic disorders such as diabetes and high blood pressure, which sometimes can contribute to preterm birth. When a woman receives adequate prenatal care, problems usually can be identified early and treated, to reduce the risk of preterm birth. A 1996 study suggested that consuming the recommended amount of folic acid throughout pregnancy may reduce the risk of preterm birth. A woman should avoid alcohol, smoking and illicit drugs beginning before pregnancy and throughout pregnancy.
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