did treatment of down syndrome change after prenatal testing and selective abortion was normalized in public health

Yes. Once prenatal testing became routine, the main "treatment" offered for Down syndrome became termination, and the numbers show it.

The clearest evidence is a systematic review of termination rates after a prenatal diagnosis of Down syndrome. Pooled across ten studies, about 92 in 100 pregnancies with a Down syndrome diagnosis were terminated, and the rate stayed stable over time rather than falling [2]. That is not a fringe finding. It is the published record of what testing plus the option of abortion actually produces.

A national Cuban program shows the same machinery at work. Of pregnancies where a chromosomal abnormality was detected, 88.5 in 100 were terminated, and Down syndrome made up 47.2 in 100 of the abnormalities found [3]. Cuba's Down syndrome live-birth rate sat around 7 to 8 per 10,000 births [3]. The authors tie that low prevalence directly to high termination after diagnosis [3]. Meanwhile a Dutch modeling study found that rising screening can coexist with rising live births, because more older mothers and incomplete uptake offset the terminations [1]. So the effect is real but not automatic.

What this retrieval does not show is the other half of your question: whether actual care for children born with Down syndrome changed, for better or worse, in the same period. No record here measures that. The evidence covers the selection side, not the treatment side.

My call: prenatal testing normalized selective abortion and reshaped the Down syndrome birth population, but the records here say nothing about whether the care of those who are born improved. Confidence: moderate on the selection effect, low on the care question.