In many cases, the reasons for birth prior to 37 weeks gestation are not known. According to the Centers for Disease Control (CDC), premature birth occurs more frequently in blacks than whites and is more common in women who are younger than 18 or older than 40. Poor management of diabetes and high blood pressure can raise the risk of delivering early. Twins are more frequently born premature than singletons. The highest risk population are mothers who have a history of preterm deliveries.
Incompetent Cervix
Incompetent cervix occurs in approximately one in 100 pregnancies, according to The American Pregnancy Association. In this condition, pressure on the cervix from the weight of the growing fetus causes it to open before the baby is mature enough to be born. Reasons for this condition may include maternal DES exposure, congenital defect, or previous procedures that weakened the cervix. Because incompetent cervix is not easy to detect, women may have two or three miscarriages before the condition is diagnosed. Cerclage, a procedure in which the cervix is stitched closed, is usually done in the second trimester. Stitches are removed when the pregnancy reaches 36 weeks.
Smoking and Drug Abuse
Maternal tobacco use is known to have adverse effects in pregnancy. Inhaled carbon monoxide reduces the oxygen-carrying ability of red blood cells and nicotine constricts blood vessels, impairing circulation to the placenta. Babies born to mothers who smoke have lower birth weights than non-smokers. A two-year study assessing preterm birth rates before and after a workplace smoking ban in Dublin, Ireland found a 25 percent decrease in premature deliveries after the law took effect. Methamphetamine and cocaine use during pregnancy also decrease blood flow to the placenta and are associated with low birth weight and preterm birth.
Infections
Approximately 40 percent of premature births are thought to be caused by infections, according to an article published in the January 2002 issue of American Family Physicians. Group B streptococcus (GBS) colonization of the vagina and cervix may invade the placenta, producing prostaglandins, hormones that trigger contractions. Kidney infections are also associated with preterm labor, as well as trichomonas and sexually transmitted diseases such as gonorrhea and chlamydia. Early and regular prenatal care makes detection of infections more likely, and in some cases can help prevent premature birth.
Stress
Emotional support can be crucial to a healthy pregnancy. Chronic stress, such as domestic violence, overwork, caring for other children, or the death of a loved one can lead to unhealthy coping behaviors such as skipping meals or eating too much sugar and fat. Cedars-Sinai reports that stress is a cause of premature birth and suggests that a history of stress before and during pregnancy may lead to preterm labor.
References
- American Pregnancy Association: Incompetent Cervix
- CDC: Preterm Birth
- "BJOG"; Low birthweight and preterm birth rates 1 year before and after the Irish workplace smoking ban; Kabir Z; December, 2009, 116(13)
- "Am Fam Physician"; Genitourinary Infections and Their Association with Preterm Labor; Cram L; Jan 15, 2002 65(2)
- Cedars-Sinai: Stress and Birth Outcomes
