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What Are the Causes of a Premature Baby?

Counted in weeks, the term of a pregnancy begins on the first day of the pregnant woman's last menstrual cycle. A normal, or term, delivery occurs anytime between weeks 37 and 42. Deliveries taking place at 43 weeks or later are post-term births, and those taking place before week 37 are preterm---or premature. According to the March of Dimes, approximately 12.8 percent of U.S. births per year are premature.

  1. Infection

    • Preterm labor caused by an infection is one of the many types of "spontaneous" preterm labors. Bacterial vaginosis, chlamydia and gonorrhea are the genital tract infections screened for during proper prenatal care, in part because they're associated with premature births. The bacteria introduced by these infections produce substances that pose a risk to the membranes around the amniotic sac, causing it to rupture and inducing labor. Should the membranes remain intact, bacteria that makes its way into the amniotic fluid could still trigger preterm labor. Trichomoniasis, or trich, can also cause premature labor, but so can its screening process, according to BabyCenter.com---so doctors only test women with symptoms.

    Illnesses and Conditions

    • Several chronic illnesses linked to premature labor include inflammatory bowel disease, lupus, chronic active hepatitis, sickle cell anemia, severe asthma and diabetes. Conditions associated with early labor and delivery include pneumonia, kidney infections and any trauma to the abdominal area---including surgery. Although associations between premature birth and certain chronic illnesses and medical conditions have been established, "in about half of all cases... providers cannot determine why a woman delivered prematurely," according to the March of Dimes.

    Other Risk Factors

    • Because it can be so difficult to determine why a woman goes into labor prematurely, a number of other factors are risks. Statistical data shows that women under the age of 17 and over the age of 35 are at increased risk, as are women carrying twins or multiples. Women who have already experienced one premature birth are at greater risk for experiencing it in subsequent pregnancies. Problems with the placenta have been linked to prematurity, as have uterine and cervical structural abnormalities. Being underweight prior to conception or not gaining enough during pregnancy are risk factors. A high amount of stress, a physically demanding job, smoking, drinking and drug abuse are all connected to premature birth.

    Medical Intervention

    • Approximately 25 percent of all premature deliveries are intentional, because of medical intervention in cases of serious or life-threatening conditions. In pregnancies where the mother's and fetus's lives are at risk from severe or intensifying pre-eclampsia, health professionals will deliver the baby by cesarean. The same is true in situations when a fetus has stopped growing. Whenever possible, doctors put off necessary intervention so that the fetus has a few extra, precious days to develop.

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