We sought to evaluate the impact of later menarche on the risk of operative delivery.
We studied 38,069 eligible women (first labors at term with a singleton infant in a cephalic presentation) from the Norwegian Mothers and Child Cohort Study. The main exposures were the age at menarche and the duration of the interval between menarche and the first birth.
Poisson's regression with a robust variance estimator.
Operative delivery, defined as emergency cesarean or assisted vaginal delivery (ventouse extraction or forceps).
A 5 year increase in age at menarche was associated with a reduced risk of operative delivery (risk ratio [RR] 0.84, 95%CI 0.78, 0.89; p?