It grows due to prenatal vitamins so if you're not taking them that's probably why.
I've been takung them but havent notice a difference...
My hair has grown quite a bit, and Im only 15wks. Depending on how far along you are in your pregnancy will you notice a difference. The prenatal vitamins they say help with hair growth, however I believe its more hormonal changes within you. When you notice your hair growing you will also notice your nails growing faster than usual. I have been taking prenatal vitamins for only 3-4 wks... I would say its more hormonal changes than the vitamins, for myself atleast.
My hair didn't grow but that's because I needed a haircut, then it started growing super fast, I have to cut my nails every 2 days as well.