title: Is the natural twinning rate still declining?
authors.forename: Anne Maria
authors.initials: AM
authors.lastname: Herskind
authors.forename: Olga
authors.initials: O
authors.lastname: Basso
authors.forename: Jørn
authors.initials: J
authors.lastname: Olsen
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthe
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
mesh_terms: D000367:Age Factors; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D005298:Fertility / Q000187:drug effects*; D005299:Fertility Agents / Q000008:administration & dosage; D006801:Humans; D007246:Infertility / Q000188:drug therapy; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000187:drug effects / Q000706:statistics & numerical data*; D012042:Registries; D027724:Reproductive Techniques, Assisted; D014427:Twins
chemical_list: D005299:Fertility Agents