• Generations;
  • post-term pregnancy;
  • prolonged pregnancy

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.