If you are suggesting that decrease is proportional to an increase in abortions, I believe you would be very wrong

https://www.guttmacher.org/infographic/2018/changes-worldwid...

coupled with some estimates on population indicates the total number of abortions has gone down by about 10%.

If birth defects are passed on from parent genes, I don't think abortion can explain a constant rate of decrease. It can explain it in the 'kill all the defective' sense (Iceland), but not 'cleaning the gene pool' sense.

"Folic acid"

Zero sum, huh?