Preterm labor and delivery can happen to any pregnant woman. But it happens more often to some women than to others. Researchers continue to study preterm labor and birth. They have identified some risk factors, but still cannot predict which women will give birth too early. Having a risk factor does not mean a woman will have preterm labor or preterm birth.

Three groups of women are at greatest risk of preterm labor and birth:

• Women who have had a previous preterm birth
• Women who are pregnant with twins, triplets or more
• Women with certain uterine or cervical abnormalities

If a woman has any of these three risk factors, it's especially important for her to know the signs and symptoms of preterm labor and what to do if they occur.

Lifestyle and Environmental Risks
Some studies have found that certain lifestyle factors may put a woman at greater risk of preterm labor. These factors include:

• Late or no prenatal care
• Smoking
• Drinking alcohol
• Using illegal drugs
• Exposure to the medication DES
• Domestic violence, including physical, sexual or emotional abuse
• Lack of social support
• Extremely high levels of stress
• Long working hours with long periods of standing

Medical Risks
Certain medical conditions during pregnancy may increase the likelihood that a woman will have preterm labor. These conditions include:

• Infections (urinary, vaginal, sexually transmitted; possibly others)
• 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
• Short time period between pregnancies (less than 6-9 months between birth and the beginning of the next pregnancy)

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. Experts do not fully understand why and how these factors increase the risk that a woman will have preterm labor or birth.

May 2007