What is preterm birth?
Preterm birth is defined as birth before the 37th week of gestation, calculated from the first day of the woman's last normal menstrual period. A baby is considered full term if born within 2 weeks of the "due date", (40 weeks after the last period). The smallest preterm babies (weighing below 1500 grams) are two hundred times more likely to die in the first year of life than babies born weighing greater than 2500 grams. Even if they survive, these very small infants are at 10 times greater risk of long term problems such as vision and hearing complications, chronic lung disease, cerebral palsy, and other neurological disorders.
What is preterm labor?
Preterm labor is defined as regular contractions of the uterus, plus a change in the amount of opening and thinning of the cervix before the 37th week of gestation. A woman's perception of her contractions varies, and studies have not shown that routinely examining the cervix duringpregnancy is helpful in detecting preterm labor. Maternity care providers struggle with the diagnosis. Half of all women with a diagnosis of preterm labor (they have contractions and cervical change) go on to full term pregnancy without any treatment. Twenty percent of women who don't meet the criteria for preterm labor (they have contractions, but their cervix doesn't change, for example), come back to deliver preterm anyway.
What causes preterm labor and birth?
Despite serious efforts to reduce preterm birth, there is little good news. Factors that start a normal, term labor are poorly understood, and preterm labor is more perplexing. Researchers have tried to identify the causes of preterm labor and birth, the women who are at risk, and ways to prevent or treat preterm labor. Very few clear answers have emerged. Most often, the cause of preterm labor is unknown. Sometimes malformations of the uterus or cervix are associated with early delivery. Often these are unknown to the woman prior to becoming pregnant. Even if known, how much a uterine fibroid or unusually shaped uterus will affect the pregnancy is often difficult to predict.
