I got ones when my wired bras became too uncomfortable. I think I was about 26 weeks pregnant. It really depends on your body. My bump was small and my body didn't change much. I still wear my originals for comfort
I've got mine at M&S at 36 weeks! Very comfortable and cosy, and M&S are brilliant in helping out!
Im a 32 GG had my maternity bras from 18 weeks as they were all uncomfortable I hated the clasps so got seam free ones from H&M and Amazon most comfiest bras and reasonable prices too if you need to upsize but they’re not necessary ’supportive’
I didn't bother with them I just upped the cup size
I'd try and stick to seamless bralette styles right now if you can (size and support needs dependent of course), they will continue to grow and might even get bigger if you plan to breastfeed. I've gone up a cup size so far and I'm almost 37 weeks. Not a clue if they will balloon when I breastfeed but I've been in and out of sizes throughout. Definitely found the seamless ones easier to wear.
If yours is still fitting, then I'd wait. I know at like 30 weeks I went from a Med to a Large and then after birth I went from a large to XXL. Now I'm back to a medium bra size.
Marks and Spencer
Would recommend (if they’re available in the UK) the kindred bravely nursing bras (especially if you plan on breastfeeding) they are sized s-xxl however they also come in busty sizes and they are very comfortable.
I went at 24 weeks to be measured as mine were not fitting correctly. The lady at the shop advised to not get fitted for a maternity bra until I was around 35-36 weeks as if I brought one earlier I would likely need to get another one later on. Instead she measured the size I was then and I went online and brought one in that size on sale. I'm currently 29 weeks and the one I purchased no longer fits well so I would recommend waiting until later if you can. I found that a cheap pack of bra extenders has worked well to extend the wearability of the one I purchased.