Increased parity does not increase the risk of Down’s syndrome

In response to a suggestion that increased parity may be an independent risk factor for Down’s syndrome, Chan et al examined South Australian data to assess the effects of parity, gravidity, and previous miscarriage (p 923). They found no increase in risk with increase in parity or gravidity or number of miscarriages. Maternal age remained the main risk factor. An analysis for trends in screening and diagnosis of Down’s syndrome in England and Wales by Mutton et al (p 922) showed that registrations rose from 1081 in 1989 to 1336 in 1997 despite a fall in the overall number of births. The proportion of cases diagnosed prenatally rose from 30% to 53%. The maternal age specific risks of Down’s syndrome remained similar to those before the availability of prenatal diagnosis: the higher numbers are accounted for partly by mothers starting families later in life.