What causes it. Doctors aren't sure, but risk factors include carrying multiple fetuses, a history of premature labor, an abnormality of the cervix, and certain vaginal infections.
Symptoms. See your physician right away if you notice bloody or watery vaginal discharge or experience abdominal cramps or backache.
Treatment. Bed rest can sometimes reduce pressure on the cervix, making it less likely to dilate. But a new study indicates that bed rest may do more harm than good in some situations, so ask your doctor whether it's necessary. "We also encourage drinking lots of fluids, because dehydration can cause uterine contractions," says Iffath Hoskins, M.D., executive director of the Women's Services Memorial Health Medical Center, in Savannah.
Can you prevent it? Reduce your risk by having your thyroid checked before getting pregnant. Women who have untreated thyroid disease are more likely to deliver prematurely. Before you conceive, it's also important to get screened for bacterial vaginosis, which has been linked to premature birth. Stress-management techniques such as yoga can also help, because several studies have found a link between high levels of stress hormones and preterm delivery rates. Finally, if you have a history of preterm delivery, ask your doctor about progesterone shots, which may reduce the risk of premature birth by almost 20 percent.