title: Increasing twinning rates in Norway.
authors.forename: Björn
authors.initials: B
authors.lastname: Westin
mesh_terms: D002940:Circadian Rhythm; D004641:Emigration and Immigration; D005260:Female; D005843:Geography; D006801:Humans; D009664:Norway / Q000453:epidemiology; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data*; D012959:Socioeconomic Factors; D014429:Twins, Dizygotic