When a woman goes into labor, she starts having uterine contractions, the amniotic sac ruptures and birth is imminent. Since normal human gestation lasts between 37 to 42 weeks, the start of labor before the 37th week of pregnancy is considered to be premature labor, or preterm labor. In some cases, premature labor can be halted using medical means, but it often proceeds to birth, resulting in a premature baby. Premature labor before the 34th week of pregnancy is especially dangerous, according to Baby Center.
Multiple Gestation
Women carrying twins, triplets or more are at a higher likelihood of going into premature labor than mothers carrying one baby. The Nemours Foundation maintains that almost 50 percent of twins are born before the 37th week of gestation, often between weeks 35 to 37. Women carrying multiples are often advised to stay off their feet as much as possible, or are even put on bed rest, from about 28 weeks of pregnancy to help prevent preterm labor.
Infections
According to Baby Center, certain bacterial infections, such as chlamydia, bacterial vaginosis and trichomonaiasis, can potentially cause premature labor. Most women are tested for genital tract infections during pregnancy, but if an infection is not detected or treated the bacteria can get into the amniotic sac or weaken the sac and cause a premature rupture of the membranes that initiate labor. Any infection, bacterial or viral, that leads to a fever over 101 degrees Fahrenheit can also cause a woman to go into labor prematurely, according to Sutter Health.
Cervical or Uterine Abnormalities
Women with an extremely short cervix, less than 25 millimeters, can have problems carrying a pregnancy to term and may go into premature labor. Some women whose mothers were given the drug diethylstilbestro, or DES, during pregnancy grow up to have a short cervix that predisposes them to premature labor, explains Sutter Health. Women with cervical insufficiency, a condition that causes the cervix to thin out as pregnancy progresses, may also be at risk for delivering prematurely. A very large or misshapen uterus is another potential cause of preterm labor.
Placental Problems
In some cases, the placenta grows abnormally, such as growing downward to cover the opening of the cervix, which can induce premature labor. In other women a condition called placental abruption, in which the placenta detaches from the side of the uterus, causes preterm labor to begin.
Mother's History
Previous procedures or events in a woman's history can add to the risk of premature labor caused by damage done to the cervix or uterus. Women who have had two or more second trimester abortions or miscarriages may go into labor before 37 weeks' gestation. Women who have had a cone biopsy or LEEP procedure done to test for cervical cancer are also more likely to have preterm labor.
