This is actually a part of the story.

Heavy axe and blade females become very fierce no matter how sweet they usually are.

They're use to being strong, but to some pregnancy is a weakening thing, so they become more violent to be under-estimated. It's because some actually think they can just run up on a preg'd woman and take advantage of them somehow.

When a female gets far enough into the stages she's no longer allowed to fight, so there's no use in wearing the armor. You can't tell a pregnant warrior female from otherwise, until you've upset them and they react by kicking your ass.

Heavy females will gladly kick your ass themselves, where as other types might have someone get you for them. As a Heavy it's natural for them to want to fight, and given the opportunity THEY WILL. They may try to start off kind, but if pressured or over whelmed they'll react outrageously. Some may react lightly so some comments, but NEVER saying anything remotely disrespectful about the child(ren) they're carrying.

No matter how violent they become in pregnancy they return to their normality after having the child(ren).