Ttc girlfriend trans mtf

Hi so I'm wondering if my girlfriend (MTF) and I ( I'm cis female) can still have a baby once she's on hormones? She hasn't started taking them yet and we're gonna have a baby before she starts them but I'm wondering if we decide to have another baby after she's taking the hormones if we can still conceive? I know that estrogen obviously has affects on sperm but is it a for sure that we couldn't have a baby? Thanks everyone!(: