title: Down syndrome and parity.
abstract: OBJECTIVE
  To investigate the effect of parity on Down syndrome (DS).
  
  
  METHODS
  The study was conducted on data from Northeast Italy (NEI) (1981-1996) and Sicily (ISMAC) (1991-1996) Congenital Malformation Registries. In these areas, all DS births are recorded and confirmed by chromosomal analysis; the NEI Registry also registers pregnancy terminations (TOPs) after prenatal diagnosis of DS. In order to estimate the effect of parity independently of the mother's age and to reduce the truncation effect, different age classes and three classes of parity (1, 2-4, >4) were defined.
  
  
  RESULTS
  The study sample consisted of 1,088 consecutive newborns and 169 consecutive fetuses affected by DS. In both NEI and ISMAC samples, we found a significantly increased risk of having a DS child for multiparas > or =35 years of age. In the NEI sample, the inclusion of TOP data did not seem to modify this finding. In the ISMAC sample, a significantly reduced risk for primiparas was found at all ages.
  
  
  CONCLUSIONS
  Our data confirm a higher risk of having a DS child in women with parity >4. As this effect is evident only in women > or =35 years age, its practical impact is null because these women are usually offered prenatal diagnosis in any case. However, the mechanisms involved, if this association is true, are very intriguing and the observation should stimulate scientific studies allowing a better knowledge of the nondisjunction mechanism.
authors.affiliation: Servizio di Genetica Clinica ed Epidemiologica, Dipartimento di Pediatria, Università di Padova, Italy. clementi@child.pedi.unipd.it
authors.forename: M
authors.initials: M
authors.lastname: Clementi
authors.forename: S
authors.initials: S
authors.lastname: Bianca
authors.forename: F
authors.initials: F
authors.lastname: Benedicenti
authors.forename: R
authors.initials: R
authors.lastname: Tenconi