Risk of labor dystocia increases with maternal age irrespective of parity: a population-based register study

Advanced maternal age is associated with labor dystocia (LD) in nulliparous women. This study investigates the age-related risk of LD in first, second and third births.

All live singleton cephalic births at term (≥ 37 gestational weeks) recorded in the Swedish Medical Birth Register from 1999 to 2011, except elective cesarean sections and fourth births and more, in total 998 675 pregnancies, were included in the study. LD was defined by International Classification of Diseases, version 10 codes (O620, O621, O622, O629, O630, O631 and O639). In each parity group risks of LD at age 25-29 years, 30-34 years, 35-39 years and ≥ 40 years compared with age < 25 years were investigated by logistic regression analyses. Analyses were adjusted for year of delivery, education, country/region of birth, smoking in early pregnancy, maternal height, body mass index, week of gestation, fetal presentation and infant birthweight.

Rates of LD were 22.5%, 6.1% and 4% in first, second and third births, respectively. Adjusted odd ratios (OR) for LD increased progressively from the youngest to the oldest age group, irrespective of parity. At age 35-39 years the adjusted OR (95% CI) was approximately doubled compared with age 25 and younger: 2.13 (2.06-2.20) in first birth; 2.05 (1.91-2.19) in second births; and 1.81 (1.49-2.21) in third births.

Maternal age is an independent risk factor for LD in first, second and third births. Although age-related risks by parity are relatively similar, more nulliparous than parous women will be exposed to LD due to the higher rate.