Hi @AnonymousNurse. I am going through something very similar too. My hair started thinning gradually from around 18 weeks pregnant - it just seemed looser at first. I avoided washing/brushing it more than absolutely necessary, and a midwife told me it was normal so I crossed my fingers and hoped it would pass (my hair was pretty thick so I could afford to lose some). Eventually another midwife suggested I consult a GP, so I did, and a blood test showed my thyroid etc. were normal, but my iron was 'slightly low' (that was at about 25-26 weeks). I started taking iron supplements, but by 27 weeks the hair on the top of my head, around my part, was noticeably thin. Now I am 30 weeks and the hair on nearly my entire scalp is conspicuously thin - it's very dramatic and looks as if I am balding. I wear a thick headband or hat whenever I go out, but I'm going to have my OH cut off the remaining long bits soon.
Last week I saw an obstetrician and got some more blood tests (supposedly more detailed ones relating to thyroid, B12, perhaps something else) and haven't got the results yet. While I was there she consulted two of her colleagues - another obstetrician and an endocrinologist - and they all agreed that if nothing came up in the new tests, it was 'a mystery' and probably just down to hormones. I suppose it could also have been the slight iron deficiency, or a combination of factors, although the iron supplements haven't stopped me from losing hair (maybe because I need to lose it all before I can start growing it back? Not sure). The obstetrician said it didn't look like alopecia (I haven't been losing it in patches, just an overall thinning), and thought she could spot new hair growth among the shorter hairs on my scalp. But anything long, it looks like I'll lose.
This is really unpleasant and upsetting, I know, and I hope you're coping with it as well as possible. I'm up and down myself - I feel all right about it so long as I don't stare at myself in the mirror for too long or think about it too much.
Anyway, since I was reading through this thread in a desperate attempt to find any info on hair loss during pregnancy, and saw your recent comment, I thought I'd share! It's reassuring to know there are others in similar situations.
@Swan8, I'd also love to know how you got on after pregnancy.
All the best! X