By Elaine Brown, MD
Preterm labor is labor on or before 37 completed weeks of pregnancy (normally pregnancy is 40 weeks long).
Infants born prematurely (especially before 32 weeks) are more likely to suffer complications such as cerebral palsy, chronic lung disease, visual disturbances, and hearing impairment.
Symptoms of preterm labor include:
There are four major pathways that lead to preterm birth:
Many doctors give their patients a single injection of terbutaline when she presents to the hospital with contractions. If labor stops completely with one injection, it was probably a false alarm. If contractions continue, additional diagnostic tests may be used to help sort out true from false pre-term labor. Some of these are:
If it appears that delivery may be imminent, magnesium sulfate is typically administered to the mother. Magnesium sulfate is given by IV in the attempt to stop true preterm labor long enough to transfer the mother to a tertiary care hospital (a major or specialty hospital) with a neonatal intensive care unit (NICU) that is capable of caring for premature infants. Recent studies have indicated that magnesium sulfate, in addition to slowing labor, has a protective effect of stabilizing delicate fetal blood vessels, especially those in the brain. When administered to mothers who deliver prematurely, it reduces the risk of cerebral palsy (a neurologic disorder) and necrotizing enterocolitis (a severe infection of the bowel) in their infants.
During this time period, corticosteroids are often also administered. Corticosteroids, such as beta methasone, help the fetal lungs to mature quickly, reducing the newborn's need for oxygen. Oxygen delivered in high concentrations for prolonged periods of time is associated with vision problems and hearing impairment.
The following groups of women are at highest risk for preterm delivery:
Finally, other factors associated with preterm delivery are vaginal bleeding, urinary tract infection during the current pregnancy, sexually transmitted infections, smoking and periodontal disease.
Recent studies have shown that administration of 17 alpha hydroxyprogesterone caproate (typically given to mothers with a history of preterm birth in a previous pregnancy) statistically reduces preterm deliveries.
Cervical cerclage (a suture similar to a purse string which is placed around the cervix) has also been demonstrated to reduce the number of preterm births. A cerclage can be used for women who have a history of preterm delivery and who have not responded to progesterone therapy.
The incidence of preterm birth in the United States increased by 20% between 1990 and 2006. Although much of this increase was due to an increase in multiple gestations resulting from assisted reproductive technologies (such as IVF) — multiple pregnancies increased by 22% over approximately the same time period — newer and more effective strategies are needed to address preterm labor and birth.
Current research is increasing our understanding of the mechanisms that cause preterm birth. As this knowledge increases, our ability to diagnose, treat and prevent preterm birth should improve substantially. There is good news too for those who go on to deliver early despite intervention: Our ability to care for premature infants, even extremely tiny babies (22-23 weeks), has resulted in increased survival of preterm infants with fewer disabilities.
Dr. Elaine Brown completed her residency in obstetrics and gynecology at Harvard. She has more than 15 years of experience in private practice.
Published March 6, 2014