Estimating recurrence of spontaneous preterm delivery

To identify factors associated with spontaneous preterm birth and to estimate the risk of its recurrence for the second through fourth births among women in Utah who had a first and any subsequent birth between 1989 and 2001, using a retrospective cohort study design.

Utah state birth records were reviewed to identify women with a first live birth and at least one subsequent live birth from 1989 to 2001. Recurrence risks for spontaneous preterm birth were calculated for first through fourth births. Then all parties (1-12) and multiple maternal risk factors were used to estimate recurrence risks for pre-term birth outcomes by multinomial regression. Recurrence risks for early and late spontaneous preterm birth were calculated. Recurrence also was evaluated as the fraction attributable to previous spontaneous preterm birth. Using the identified factors, the sample was divided and the model was estimated for a subset of births (1989-1999); its predictive value was tested on the remaining births (2000-2001).

Women who experienced a spontaneous preterm birth before 34 weeks of gestation in their first or second live birth had the highest rate of recurrence. Spontaneous preterm birth before 34 weeks was the highest risk factor for recurrence of early spontaneous preterm birth (relative risk 13.56, 95% confidence interval 11.5-16.0), and, in general, risks were highest for recurrences of same gestational age outcomes.

A history of a live spontaneous birth before 34 weeks of gestation is a strong predictor of subsequent spontaneous preterm birth. A model of clinical risk factors may be used to identify women at increased risk for recurrent spontaneous preterm birth.