The prevalence does not continue increasing at an increasing rate with age above age 45 as has been previously assumed. Above this age the rate of increase declines with increasing age. The overall age pattern is sigmoidal. A new logit logistic model is proposed which fits the data well. The risk of a Down's syndrome live birth is given by: risk=1/(1+exp(7.330-4.211/(1+exp(-0.282x(age-37.23))))).
Objectives To describe trends in the numbers of Down’s syndrome live births and antenatal diagnoses in England and Wales from 1989 to 2008.Design and setting The National Down Syndrome Cytogenetic Register holds details of 26488 antenatal and postnatal diagnoses of Down’s syndrome made by all cytogenetic laboratories in England and Wales since 1989.Interventions Antenatal screening, diagnosis, and subsequent termination of Down’s syndrome pregnancies.Main outcome measures The number of live births with Down’s syndrome.Results Despite the number of births in 1989/90 being similar to that in 2007/8, antenatal and postnatal diagnoses of Down’s syndrome increased by 71% (from 1075 in 1989/90 to 1843 in 2007/8). However, numbers of live births with Down’s syndrome fell by 1% (752 to 743; 1.10 to 1.08 per 1000 births) because of antenatal screening and subsequent terminations. In the absence of such screening, numbers of live births with Down’s syndrome would have increased by 48% (from 959 to 1422), since couples are starting families at an older age. Among mothers aged 37 years and older, a consistent 70% of affected pregnancies were diagnosed antenatally. In younger mothers, the proportions of pregnancies diagnosed antenatally increased from 3% to 43% owing to improvements in the availability and sensitivity of screening tests.Conclusions Since 1989, expansion of and improvements in antenatal screening have offset an increase in Down’s syndrome resulting from rising maternal age. The proportion of antenatal diagnoses has increased most strikingly in younger women, whereas that in older women has stayed relatively constant. This trend suggests that, even with future improvements in screening, a large number of births with Down’s syndrome are still likely, and that monitoring of the numbers of babies born with Down’s syndrome is essential to ensure adequate provision for their needs.
Mortality and cancer incidence were assessed in a cohort of 1373 patients with numerical sex chromosome abnormalities diagnosed at three cytogenetics centres in Britain during 1959-90, and were compared with expectations from national rates. Four hundred patients with Turner's syndrome were followed, of whom 62 died, with a relative risk (RR) of death of 4.16 (95 % confidence interval (CI) 3.22-5.39). Turner's syndrome patients had greatly raised risks of death from diseases of the nervous, cardiovascular, respiratory, digestive and genitourinary systems. One hundred and sixty three deaths occurred among 646 patients with Klinefelter's syndrome with a 47,XXY constitution, giving an RR of 1.63 (1.40-1.91). Mortality in these patients was significantly raised from diabetes and diseases of the cardiovascular, respiratory and digestive systems. There was also significantly increased mortality for patients with X polysomy (RR l 2.11 (1.43-3.02)) and Y polysomy (RR l 1.90 (1.20-2.85)), the former with significantly increased mortality from cardiovascular disease and the latter from respiratory disease. The only significantly raised risks of cancer incidence or mortality in the cohort were for lung cancer and breast cancer in patients with Klinefelter's syndrome with a 47,XXY constitution, and non-Hodgkin's lymphoma in men with more than three sex chromosomes.
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