This very much enters the realm of medically justified abortion. Of course there are issues of properly determining real risk and actual microcephaly. Because we do have modern techniques we no longer have the option of taking a failed birth child out onto a hillside to allow death by exposure. Unfortunately that never meant we had the ability to prevent the situation in which this was the solution.
Abortion is our modern solution and it has the benefit of been private. Babies will be conceived who have no possibility of living a full human life. As it is we err on the side of caution and sustain a small population of the mildly retarded usually well engaged and perhaps even happy. All well and good.
It is those who have no hope at all that are so troublesome. They are very much the walking dead. If that can be identified early then abortion is truly a blessing for all. Identification is the real problem here. Just when do we know that the fetus is affected? These are terrible decisions and abortion has been applied to huge numbers healthy viable fetuses so the choice is very much available even if no proof exists yet.
The real question that must be addressed is this. Can the spirit body operating this life make any life progress in view of current conditions. If the true answer is no, then we are responsible for releasing that spirit body as soon as plausible. It may become easier seen that way and truly applies to the whole question of medical euthanasia. Once the spirit body is effectively trapped the body serves no further purpose except as a prison...