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Preterm Labor

Preterm labor is defined as regular uterine contractions with progressive cervical change or regular uterine contractions with a cervix that is 2 cm dilated and 80% effaced at less than 37 weeks gestation. Preterm labor is a major cause of preterm delivery. Birth is the cause of 80% of neonatal deaths that are not due to congenital malformations.

Etiology and Epidemiology

Predisposing Factors

The cause of most cases of labor is unknown. Risk factors include low socioeconomic status, nonwhite race, maternal age of 18 years or less or of 40 years or more, and low prepregnancy weight.

Multiple gestations account for 10% of all births even though they account for only 1.1% of all pregnancies.

A history of one previous birth is associated with a recurrence risk of 17-37%.

Women who have experienced one or more spontaneous second-trimester abortion are at increased risk for subsequent deliveries.

Maternal smoking, cocaine use, and lack of prenatal care are associated with delivery.

Other conditions that lead to early prematurity include premature rupture of membranes, maternal complications, and antepartum fetal compromise.

Uterine Causes of Prematurity

Uterine malformations (unicornuate or bicornuate uterus) increase the risk for delivery.

Cervical incompetence affects 0.1-2% of all pregnancies. It presents as painless cervical dilation and premature loss.

Infectious Causes of Prematurity

Maternal genital tract colonization and premature infection are important causes of births.

An increased rate of prematurity delivery occurs in women with cervical colonization with group B streptococci, Neisseria gonorrhoeae, Chlamydia trachomatis, Ureaplasma urealyticum, Treponema pallidum, Trichomonas vaginalis, prematurity or Gardnerella vaginalis.

Treatment