The normal human gestation period is 40 weeks. Delivery of an infant prior to 37 weeks is considered a premature birth. Premature birth places the child at greatly increased risk of death or permanent physical, learning and behavioral difficulties. The March of Dimes explains that most cases of premature delivery happen spontaneously, while a quarter of them are induced or delivered by Cesarean section due to risk to the baby or mother. Some causes of prematurity can be controlled by the mother or the obstetrician. Good prenatal care is vital throughout every pregnancy.
Maternal Medical Problems
The University of Virginia Health System reports that pre-existing heart or kidney disease increases the risk of premature birth. Diabetes and obesity are other frequent causes. Urinary tract infections, sexually transmitted diseases and vaginal infections also increase the odds of an early delivery. Hypertension (high blood pressure) and blood clotting disorders are implicated in some cases.
Reproductive Causes
Pre-eclampsia, a condition in which the mother develops high blood pressure serious enough to cause protein in her urine, often leads to premature birth. Placenta previa, in which the placenta is too low in the uterus, often prevents a baby from being able to be carried to full term. Placental abruption occurs when the placenta detaches from the uterus sooner than it should, often requiring a mandatory delivery to save the baby. Some women have a condition called incompetent cervix; in this situation the cervix--which should remain closed--becomes weak as the baby grows. The cervix slowly begins to open and the baby may not be able to be carried to term. Often, the obstetrician places a stitch in the cervix in an attempt to correct the problem or give the baby more time in the womb. Some uteruses have genetic or other defects. An infection can also be present inside the amniotic membrane. Other serious problems that often lead to premature delivery include polyhydramnios, in which too much fluid is present in the amniotic sac, and a spontaneous early rupture of the sac. This early rupture may precipitate labor, or the obstetrician may decide to take the baby soon after. Carrying twins, triplets or more fetuses increases the odds that delivery will occur pre-term.
Other Maternal Conditions
Expectant mothers who are 17 years old or younger are at higher risk for delivering prematurely. Women over age 35 are also at higher risk. Women who are underweight or malnourished prior to becoming pregnant are more likely to have a early birth, as are women who eat poorly during the pregnancy. A lack of prenatal care increases the odds, as does obesity. Having a child before the body has had a chance to recover from a prior pregnancy is another cause of premature birth. Women who stand for hours most days of the week also place themselves at risk. Increased emotional stress is implicated in some cases of prematurity. Using drugs, such as alcohol, cocaine, tobacco or amphetamines, is also known to cause premature birth.
Other Causes
Babies with serious birth defects are often born prematurely. In some cases, the cause is never determined. The obstetrician tries to control this unless the fetus is in distress. Women who have had previous preterm deliveries are, unfortunately, at increased risk of it happening again.
