I'm Dr. Peter Heyl, a maternal-fetal medicine specialist at Eastern Virginia medical School. The duration of a normal pregnancy is about 38 to 40 weeks, but sometimes the uterus begins regularly contracting too early, when the fetus is not yet ready for life outside the womb. This condition, pre-term labor, if not stopped, can lead to disease and even death for the newborn, in what was previously a healthy pregnancy.
Premature labor has many possible causes.
It is more common in pregnancies that involve more than one fetus, such as twins, triplets, or more. This is probably due to over-distension of the womb, which can also occur when there is an excessive amount of amniotic fluid in the bag of waters. An incompetent cervix may start to open up, or dilate, with minimal or no uterine contractions. And smoking, substance abuse, or poor nutrition greatly increase the chance that pre-term labor will occur. Finally, a large number of premature births are associated with infections of the reproductive tract, caused by such organisms as chlamydia, trichomonas, and bacterial vaginosis.