PubMed · 4845939
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R Freedman, B Berelson. 1974. The human population.. https://doi.org/10.1038/scientificamerican0974-30
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The aims of the present study were to determine recent trends in the prevalence of Down syndrome (DS) in Japan, and to determine whether recent changes in demographic and social habits and access to prenatal diagnosis have influenced the livebirth rates of DS. Livebirth statistics indicate that the birth rate in Japan has decreased for women in their 20s and has increased for those in their 30s and 40s. During an 18-year period between 1980 and 1997, 1,299 consecutive DS infants were born among a total of 2,232,694 births, a rate corresponding to approximately 10% of all births in Japan over the same period. The increasing risk of DS with advancing maternal age was confirmed. The overall prevalence was 5.82 DS births per 10,000 livebirths (8.3-9.7 per 10,000 after correction according to the estimated ascertainment ratio: 60-70%). The prevalence rate by year of child birth represents a statistically significant increase (P = 0.001). In conclusion, recent trends in the prevalence of DS in Japan from 1980 to 1997 failed to show a consistent tendency to decrease, probably because of the concomitant increase in pregnancy in advanced maternal age.
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BACKGROUND: Meta-analyses of randomized controlled trials suggest that elective induction of labour at 41 weeks' gestation, compared with expectant management with selective labour induction, is associated with fewer perinatal deaths and no increase in the cesarean section rate. The authors studied the changes over time in the rates of labour induction in post-term pregnancies in Canada and examined the effects on the rates of stillbirth and cesarean section. METHODS: Changes in the proportion of total births at 41 weeks' and at 42 or more weeks' gestation, and in the rate of stillbirths at 41 or more weeks' (versus 40 weeks') gestation in Canada between 1980 and 1995 were determined using data from Statistics Canada. Changes in the rates of labour induction and cesarean section were determined using data from hospital and provincial sources. RESULTS: There was a marked increase in the proportion of births at 41 weeks' gestation (from 11.9% in 1980 to 16.3% in 1995) and a marked decrease in the proportion at 42 or more weeks (from 7.1% in 1980 to 2.9% in 1995). The rate of stillbirths among deliveries at 41 or more weeks' gestation decreased significantly, from 2.8 per 1000 total births in 1980 to 0.9 per 1000 total births in 1995 (p < 0.001). The stillbirth rate also decreased significantly among births at 40 weeks' gestation, from 1.8 per 1000 total births in 1980 to 1.1 per 1000 total births in 1995 (p < 0.001). The magnitude of the decrease in the stillbirth rate at 41 or more weeks' gestation was greater than that at 40 weeks' gestation (p < 0.001). All hospital and provincial sources of data indicated that the rate of labour induction increased significantly between 1980 and 1995 among women delivering at 41 or more weeks' gestation. The associated changes in rates of cesarean section were variable. INTERPRETATION: Between 1980 and 1995 clinical practice for the management of post-term pregnancy changed in Canada. The increased rate of labour induction at 41 or more weeks' gestation may have contributed to the decreased stillbirth rate but it had no convincing influence either way on the cesarean section rate.