Low folate can be linked to anaemia, so I'm sure they will be keeping an eye on that. Folic acid is the synthetic form of folate, which is only stored in our body temporarily, so that's why we need to keep taking vitamins or eating folate-rich foods. Deficiency can happen if you are low on your intake even for a few weeks - so perhaps HG has contributed to it if you were unable to keep down foods and vitamins recently? Are you feeling better with it now or still suffering?
If you are able to keep any food down you could try foods naturally high in folate as well as the supplements - broccoli, cauliflower, sprouts, peas, kale, asparagus, any green leafy veg, romaine lettuce, lentils, fortified cereals etc (or the easiest one for me when I couldn't stand any veg was cantaloupe melon!) Easier said than done when you have HG though, I know!
Also I think vitamin B12 is supposed to help - either supplements or it is found in meat, fish, eggs, dairy products, marmite, cereals etc.
Hope you are feeling better soon 