It's called Linea Nigra, or the pregnancy line. Prego friend of mine had it, kinda freaked me out when I first saw it. Apparently all women have the line prior to pregnancy (linea alba), but it darkens during pregnancy and the darker your skin the darker the line can appear. Hair can also grow a bit weird during pregnancy, usually darker. I doubt it's taking hormones or T during pregnancy, your baby would probably be all kinds of fucked up, and I wouldn't think you could even get pregnant when you're pumped up on male hormones.