I agree with pink4ever. Being pro-choice does not mean that you lose the right to think that a particular choice is morally abhorrent. It doesn't even mean that you lose the right to say it. Being pro-choice means that you would argue against anyone suggests that this couple could not have an abortion. You can still believe that they should not have done so. You can support their right to choice while still condemning the choice they made.
This couple did not become pregnant by accident. Their circumstances did not change after conception. They went into this situation, presumably in full knowledge that there was a 50% chance the resulting child (or potential child depending on your view) would be discarded in favour of another attempt. The most charitable interpretation would be that they did not realise that they would feel so strongly until they found out that they were having a boy.
I think that this type of decision is ever considered acceptable is fairly indicative of what a throw-away culture we have become, These embryos were aborted not because of anything that would impact upon their quality of life, nor because of anything that would make the family life difficult, but simply because they were not what the parents wanted.
I have enormous sympathy for the parents. I can't imagine what it woud be like to lose a child. But you can't replace a child. If they had decided to have another child because their family felt incomplete, or because the other children were now lonely, or because they simply wanted to experience being the parents of a new child once again, I would have more sympathy, although I would still be concerned about the possibility of the new child not living up to expectations. It is a big responsibility for that child to heal the family. But they are trying to recreate a particular facet of their lost child's identity - albeit a big one in gender. What if they wanted to recreate an attractive child, or an outgoing child, or a funny child?
I support their right to make the decision but I loathe the fact that this was what they chose. I also do not know what possessed them to go to the papers. Some things should be private.