title: The epidemiology of multiple births.
abstract: On the basis of MEDLINE and manual searches, we examined the main papers in the English literature regarding risk factors for spontaneous (i.e. not related to fertility drug use) multiple births. The constant frequency of monozygotic (MZ) pregnancies over time and in different geographical areas suggests that the determination of MZ twins is largely unchanged over time, and that a genetic mechanism may have a role. In contrast, temporal and geographical trends observed in dizygotic (DZ) pregnancies suggest that environmental factors play a role in determining this condition. At present, maternal age and hereditary components are the best-defined determinants for spontaneous multiple births.
authors.affiliation: Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Bortolus
authors.forename: F
authors.initials: F
authors.lastname: Parazzini
authors.forename: L
authors.initials: L
authors.lastname: Chatenoud
authors.forename: G
authors.initials: G
authors.lastname: Benzi
authors.forename: M M
authors.initials: MM
authors.lastname: Bianchi
authors.forename: A
authors.initials: A
authors.lastname: Marini
mesh_terms: D000367:Age Factors; D003241:Consanguinity; D003276:Contraceptives, Oral / Q000008:administration & dosage; D005260:Female; D006801:Humans; D008019:Life Style; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000208:ethnology / Q000235:genetics / Q000706:statistics & numerical data*; D044469:Racial Groups; D017584:Reproductive History; D012307:Risk Factors; D012923:Social Class; D013997:Time Factors; D014427:Twins / Q000706:statistics & numerical data
chemical_list: D003276:Contraceptives, Oral