It is most definitely an interesting case. If the pregnant girl had nothing to do with the spiking of her drink, then I would have to say that, in my opinion, the perp should be charged with attempted murder.
I want to say there are degrees of attempted murder just as their are degrees of murder While, PJ, you could be correct in that the intent was not to kill the unborn child, I still think one would have to argue for second degree or at least attempted manslaughter (does that exist?)
However, someone already said it: that option will most likely not be pursued. It will be easier for a prosecutor to get a conviction of assault/aggravated assault, then to swing a jury in what would turn in to a highly politicized circus trial...