In nearly 4 out of 10 premature births, the cause is unknown. But researchers have made some progress in learning the causes of prematurity. Studies suggest that there may be four main routes leading to premature labor:
1.
Maternal or fetal stress: Constant stress in the mother (such as exhaustion, tension, emotional stress or abuse) appears to trigger the production of hormones that can cause contractions and premature labor. Stress in the infant (such as poor blood supply from the placenta or
birth defects) can also lead to premature labor. Medical conditions in the mother, including anemia, unhealthy diet, and diabetes, may contribute to physical stress for both mother and child during pregnancy.
2.
Infections and inflammation: Studies suggest that premature labor is often triggered by the body's natural immune response to certain bacterial infections, such as those involving the genital and urinary tracts and fetal membranes. Even infections far away from the reproductive organs, such as periodontal disease, may contribute to premature delivery.
3.
Bleeding: The uterus may bleed due to problems such as placental abruption (the placenta separates from the wall of the uterus). Bleeding triggers the release of proteins involved in blood clotting. These proteins may cause labor contractions to begin.
4.
Stretching of the uterus. An overstretched uterus is a risk factor for preterm birth. This may happen when a woman is carrying two or more babies. It can also happen when there is too much amniotic fluid (polyhydramnios) or when the uterus is abnormal.
The four routes described above are not the only things to consider. One condition that can lead to premature delivery is incompetent cervix. This means that the cervix opens too early. Doctors don't know why this occurs. For more information, read about
cervical insufficiency. Other factors, such inductions and cesarean sections, can also play a role in premature birth.
Three groups of women are at greatest risk of preterm labor and birth:
- Women who have had a previous preterm birth
- Women who are pregnant with twins, triplets or more
- Women with certain uterine or cervical abnormalities
If you have any of these three risk factors, it's especially important for you to know the signs and symptoms of preterm labor and what to do if they occur.
The article on premature labor—including causes, risk factors, prevention, and signs of labor—has more information.
August 2009
