title: Twinning rates: reply.
authors.forename: Sakari
authors.initials: S
authors.lastname: Timonen
mesh_terms: D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D005260:Female; D006801:Humans; D008027:Light; D009664:Norway; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000502:physiology*