You don't typically get to "self defense" property. Laying hands on someone, whether pushing, shoving, hitting, or whatnot only flies when that force applies to the defense of self or others, and only to the extent that the force is reasonable. When some hysterial woman, pregnant or not, throws themselves on your vehicle, you use 911 and then sue for any damages sustatained to the property.

It doesn't matter WHOSE baby it is - courts tend to look harshly upon ANY level of battery against a pregnant woman which isn't OBVIOUS self defense (again, not PROPERTY defense).