I didn't use anything aside from my ayurvedics while I was pregnant. Hair products aren't the only things you should look into. Certain body products and even certain herbs are advised against while pregnant. Definitely do your research.
I was pregnant with a girl and my hair still grew super fast. I'd henna one week, and my grays would be showing again in a week combine that with the fact that I was pregnant during the summer (my hair seems to grow better in the summer). My hair didn't really grow all that fast with my son.
And remember every woman's pregnancy is different. Chances are good that you'll get some nice growth, but that's not the case for every woman. So, I wouldn't advise getting your hopes up... just in case it doesn't happen.
As far as the shedding goes, a lot of women do start shedding around 3 months after pregnancy, and it'll mostly be hair that would've shed normally, but again, you may no shed. You'll just notice it more because it'll all be coming out ahead of time rather than here and there like it normally would. I didn't shed after my first pregnancy, but I just had my daughter almost a month ago. So, I'll the verdict's still out on the hair. I would love to keep the thickness I have now, though.
And since you're TTC, I'm sure your probably taking all the extra precautions to ensure you're healthy like taking vitamins or eating better or whatever, you hair will thrive from you taking better care of yourself for your future pregnancy, as well.
HTH, and GOOD LUCK!