The NICHD Consecutive Pregnancies Study: recurrent preterm delivery by subtype

OBJECTIVE: Attention for recurrent preterm delivery has primarily focused on spontaneous subtypes with less known about indicated preterm delivery. STUDY DESIGN: In a retrospective cohort of consecutive pregnancies among 51,086 women in Utah (2002-2010), binary relative risk regression was performed to examine the risk of preterm delivery (PTD; <37 weeks) in the second observed delivery by PTD in the first, adjusting for maternal age, race/ethnicity, prepregnancy body mass index, insurance, smoking, alcohol and/or drug use, and chronic disease. Analyses were also performed stratified by prior preterm delivery subtype: spontaneous, indicated, or no recorded indication. RESULTS: There were 3836 women who delivered preterm in the first observed pregnancy (7.6%), of which 1160 repeated in the second (30.7%). Rate of recurrent PTD was 31.6% for prior spontaneous, 23.0% for prior indicated delivery, and 27.4% for prior elective delivery. Prior spontaneous PTD was associated with a relative risk (RR) of 5.64 (95% confidence interval [CI], 5.27-6.05) of subsequent spontaneous and RR of 1.61 (95% CI, 0.98-2.67) of subsequent indicated PTD. Prior indicated PTD was associated with an RR of 9.10 (95% CI, 4.68-17.71) of subsequent indicated and RR of 2.70 (95% CI, 2.00-3.65) of subsequent spontaneous PTD. CONCLUSION: Prior indicated PTD was strongly associated with subsequent indicated PTD and with increased risk for subsequent spontaneous PTD. Spontaneous PTD had the highest rate of recurrence. Some common pathways for different etiologies of preterm delivery are likely, and indicated PTD merits additional attention for recurrence risk.