I definitely RETAIN hair during pregnancy, so I expect that "extra" hair to fall out after the hormones die down. I also credit my prenatal vitamins for the extra volume.
However, if you are concerned that it's getting thinner and thinner, talk to your doctor. There may be something missing nutritionally.. my MIL takes an OTC thyroid supplement, and she's noticed that her arm hair has finally returned, and the hair on her head is noticeably thicker.
Other ideas:
- keep taking prenatal vitamins
- use anti-hair loss shampoo/conditioner (my SIL used it when she was going through hair loss, likely from emotional stress)
- use a fine-toothed comb. get more of the shedding hair out all at once in the shower.