Risk for postterm delivery after previous postterm delivery

We examined the hypothesis that the risk for subsequent postterm birth is increased in women with an initial postterm birth.

We performed a population-based cohort study of Missouri births (1989-1997) to assess the recurrence of postterm birth using the Missouri Department of Health's maternally linked database.

A total of 368,633 births were evaluated, of which 7.6% were postterm (>42 weeks of gestation). Black mothers had a lower risk for all (adjusted odds ratio [OR], 0.70; 95% CI, 0.67-0.73) or recurrent (adjusted OR, 0.73; 95% CI, 0.67-0.79) postterm birth. Maternal education of <12 years (adjusted OR, 1.51; 95% CI, 1.41-1.62), indices of low socioeconomic status, and maternal body mass index >35 kg/m2 (adjusted OR, 1.23; 95% CI, 1.11-1.37) were associated with increased risk for recurrent postterm birth. Mothers with an initial postterm birth were at increased risk for postterm birth (OR, 1.88; 95% CI, 1.79-1.97) in subsequent pregnancies, independent of race.

Among mothers who deliver postterm, there is a significant risk for subsequent postterm births. This increased risk suggests that common factors (genetic or other) influence the likelihood of abnormal parturition timing.