Chapter 33 PRETERM LABOR
Preterm labor is the leading cause of perinatal morbidity and mortality in the United States. Preterm labor is characterized by increased uterine irritability and cervical effacement or dilatation, or both, before 37 weeks of pregnancy. Preterm labor usually results in preterm birth, which affects 8% to 10% of births in the United States. Unfortunately, in most cases, the precise causes of preterm labor are not known. Risk factors associated with preterm labor are outlined later in this chapter. Women with a history of preterm delivery have the highest risk of recurrence, estimated to be between 17% and 37%. Approximately 40% of spontaneous births following preterm labor are thought to be caused by infection. Screening and treatment for asymptomatic bacteriuria early in pregnancy, which prevents pyelonephritis during pregnancy, has helped reduce the rate of preterm delivery.
Fetal fibronectin in cervical and vaginal secretions may be a biochemical marker for preterm labor. The presence of fetal fibronectin in the cervix or vagina is infrequent after the 20th week of gestation and rare after the 24th week. After the 24th week, the presence of fetal fibronectin may indicate detachment of the fetal membranes from the deciduas. Studies suggest that fetal fibronectin is a biochemical marker for labor. However, there is no evidence to suggest that the use of the assay for fetal fibronectin would result in a reduction in spontaneous preterm birth. Many questions still remain as to how to use the results of fetal fibronectin assays, both positive and negative, in clinical care.
