The 90% rate of abortion upon prenatal discovery that a fetus likely has Down Syndrome is being quoted a lot today. Is it true? Seems like it. Termination rates after prenatal diagnosis of Down syndrome, spina bifida, anencephaly, and Turner and Klinefelter syndromes: a systematic literature review:
...Termination rates varied across conditions. They were highest following a prenatal diagnosis of Down syndrome (92 per cent; CI: 91 per cent to 93 per cent) and lowest following diagnosis of Klinefelter syndrome (58 per cent; CI: 50 per cent to 66 per cent). Where comparisons could be made, termination rates were similar in the 1990s to those reported in the 1980s.
Approximately 90% would choose TOP for lethal chromosomal abnormalities and Down syndrome while about 50% would do so for Klinefelter or Turner syndromes. Over 80% were of the opinion that women should be given the right to choose TOP for lethal congenital malformation as well as for Down syndrome after 24 weeks of gestation. This figure dropped to 55.7% for non-lethal structural malformation that requires postnatal treatment. Religious background was a significant factor for a negative attitude towards TOP.
But it's good to check your intuitions, Attitudes towards termination for fetal abnormality: comparisons in three European countries:
.... In all, more than 1,700 study participants completed questionnaires. Overall, health professionals were more likely than the lay persons to report that they would opt for termination following diagnosis of a fetal abnormality. Differences were found between countries and study groups. German respondents were least likely to report that they would undergo termination in the case of a fetal abnormality while Portuguese respondents were most likely to report that they would undergo a termination....
Finally, that doesn't mean that Down Syndrome is going to be a condition of the past, Impact of prenatal diagnosis on the prevalence of live births with Down syndrome in the eastern half of Switzerland 1980-1996:
Despite increasing prenatal detection rates of trisomy 21 foetuses (an increase of 169% in the last 5 versus the first 5 years of the study period) and subsequent termination of pregnancies, the number of liveborn Down syndrome children remained constant. The reason is a shift towards a higher mean maternal age from 28 to 30 years between 1980 and 1996. If mean maternal age at delivery was considered, the observed increase of trisomy 21 conceptions matched well with the calculated figures.