Recurrence of prolonged and post‐term gestational age across generations: maternal and paternal contribution

Please cite this paper as: Morken N‐H, Melve K, Skjaerven R. Recurrence of prolonged and post‐term gestational age across generations: maternal and paternal contribution. BJOG 2011;118:1630–1635. Objective  To estimate intergenerational recurrence risk of prolonged and post‐term gestational age. Design  Population‐based cohort study. Setting  Norway, 1967–2006. Population  Intergenerational data from the Medical Birth Registry of Norway of singleton mothers and fathers giving birth to singleton children: 478 627 mother–child units and 353 164 father–child units. A combined mother–father–child file including 295 455 trios was also used. Methods  Relative risks were obtained from contingency tables and relative risk modelling. Main outcome measures  Gestational age ≥41 weeks (≥287 days), ≥42 weeks (≥294 days) and ≥43 weeks (≥301 days) of gestation in the second generation. Results  A post‐term mother (≥42 weeks) had a 49% increased risk of giving birth to a child at ≥42 weeks (relative risk [RR] 1.49, 95% CI 1.47–1.51) and a post‐term father had a 23% increased risk of fathering a child at ≥42 weeks (RR 1.23, 95%CI 1.20–1.25). The RRs for delivery at ≥41 weeks were 1.29 (1.28–1.30) and 1.14 (1.13–1.16) for mother and father, respectively, and for ≥43 weeks 1.55 (1.50–1.59) and 1.22 (1.17–1.27). The RR of a pregnancy at ≥42 weeks in the second generation was 1.76 (1.68–1.84) if both mother and father were born post‐term. Adjustment for maternal age in both generations, fetal sex in the second generation, parity, and maternal and paternal birthweight did not influence the risk estimates. Conclusions  There is a familial factor related to recurrence of prolonged pregnancy across generations and both mother and father seem to contribute.