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.
© 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2011 RCOG.