Depends on where your empathy goes. You also have to consider the life of the one carrying the foetus, and the life that a being that is not yet sentient would get if it were to live. I don't see any inconsistency with being vegetarian in that respect.
Refusing to eat mussels but being supportive of abortion would seem inconsistent, though... As well as being fearlessly against abortion while enjoying a piece of a cow one in a while seems very inconsistent, if you set aside religious believes.
> convenience of lifestyle / avoidance of responsibility at the most callous
That was also what I was thinking of when I wrote taking into consideration the life of the unborn child. Being undesired or a burden isn't really giving someone the best chances of being happy and fulfilled. But then again, we can come up marginal cases.
"and the life that a being that is not yet sentient would get if it were to live"
I don't know that I think it's not sentient, nor that it is not yet alive. I recognise that might not accord with scientific opinion, but there it is.
Abortion is not something that you have to deal with daily, whereas food (other peoples', your own) is.
But, it would make sense perhaps, if many of the empathic vegetarians would also be anti-abortion too.