I think it's definitely possible that Scratch was a mommy. She does suddenly shift in her demeaner toward Lizzie when she sees that she's throwing up, and could recognize it as morning sickness. So there might be more to it than just the extreme bargaining chip it would be to have the pregnant girlfriend to one of the soldiers from the Tower. Although, I'm not sure how much of a maternal instinct Scratch would have.
If I may expand on Eviebae's theory a little further:
Perhaps Scratch, with her quick temper, was less-than-stellar at being a mommy, resulting in the loss of her baby/child (i.e. Shaken Baby Syndrome). She might then plan on taking Lizzie's unborn child, seeing it as a second chance or replacement for the one she lost. I have heard horror stories of women killing new mothers or even mothers-to-be and taking the baby as their own. Scratch seems like just the right kind of psycho to do something like that.