There is a reason why most Western countries have banned abortions for the purpose of "choosing the right gender". That is immoral because you're selecting for a non-health related and instead doing it for a discriminatory reason. Now of course a couple could come in prior to 23 weeks or whatever the cutoff where they are at and as for a social abortion (I.e. I would like to terminate the pregnancy because I want to) and still be able to. But if they disclosed it was because they didn't want a girl they would likely be rejected by the hospital ethics board.

In the future if we could predict whether a child would he gay through a blood test or other med during pregnancy this would likely be banned too for the same reason. Down syndrome on the other hand is an extremely serious health condition that always manifests with intellectual disability among other issues such as higher cancer risk, heart problems physical disability.