Under a similar situation with a partner Id agree. But that is the exception, not the rule. IMO the 'vote' from one parent to carry the child overrides the vote for abortion. Even if you agree with abortion, how can you agree in a fair, equal society in which men and women should have equal footing and opertunity in all walks, from the army to the home, and yet say the womens right in child bearing overrides the mans?
In the situation with the gay couple, their votewould count as one, I guess the one who was the hiological father (or mother in a reverse situation) would get the choice. But the question you highlited shows a problem with the current system. So some -itch of a women decides that she wants to back out, she is effectively killing someone elses baby with litle or no consideration for the father. A system which protects a womens right to do this is anything but fair and equal.