title: Mechanisms of twinning. V. Conjoined twins, stem cells and the calcium model.
abstract: OBJECTIVE
  To examine the possible role of calcium in conjoined twinning.
  
  
  METHODS
  Conjoined (CJ) twins are an extreme example of monozygotic (MZ) twinning. Data were collected from various sources on factors to which gravidas who deliver CJ twins were exposed around the time of conception.
  
  
  RESULTS
  A significant number of such women were subjected to environmental triggers. Of particular interest is increased CJ twinning following use of oral contraceptives. It is hypothesized that this resulted from prolonged ovulatory dysfunction in lightweight women. The incidence of uniovular twinning is inversely related to women's prepregnancy weights.
  
  
  CONCLUSIONS
  These observations are consistent with the proposed general model of MZ twinning. Factors that induce calcium depression and delayed implantation encourage uniovular duplication in general and CJ twinning in particular.
authors.affiliation: Department of Obstetrics and Gynecology, Long Island Jewish Medical Center, New Hyde Park, New York, USA. dav4601@aol.com
authors.forename: Gary
authors.initials: G
authors.lastname: Steinman
mesh_terms: D015992:Body Mass Index; D002118:Calcium / Q000097:blood / Q000494:pharmacology* / Q000502:physiology*; D005260:Female; D006801:Humans; D008954:Models, Biological; D011247:Pregnancy; D011256:Pregnancy Outcome; D013234:Stem Cells / Q000502:physiology*; D038522:Twinning, Monozygotic / Q000187:drug effects* / Q000502:physiology*; D014428:Twins, Conjoined / Q000503:physiopathology*; D014430:Twins, Monozygotic
chemical_list: D002118:Calcium