Paternal age and preterm birth.

Background: There is growing evidence that advanced paternal age can be a reproductive hazard.
Methods: We studied couples and their first children using nationwide registers in Denmark between 1980 and 1996. We restricted the analysis to mother's age 20-29 years. We estimated odds ratios (ORs) of preterm (< 37 weeks gestation) and very preterm birth (< 32 weeks) as a function of paternal age using logistic regression to adjust for potential confounding variables.
Results: The risk of preterm birth increased with paternal age, almost entirely resulting from an association for very preterm birth. Compared with fathers age 20-24 years, ORs for very preterm birth were 1.3 (age 25-29), 1.4 (age 35-39), 1.7 (age 40-44), 1.6 (age 45-49), and 2.1 (age 50+) (test for trend: P = 0.01).
Conclusions: Risk of very preterm birth increases among older fathers, perhaps as a result of a paternal placental effect.