Mine weaned in early pregnancy...maybe at the end of the first tri? Can't remember properly. But I sort of didn't fight the weaning, I'd introduced cow's milk as part of his diet, that was about a week before he turned 1. For me, it sort of had to happen, because I was losing quite a bit of weight, I think that breastfeeding and growing a new baby put a lot of demand on my body at a time when I found it really hard to eat.
That was just me though - I definitely know that pregnancy and breastfeeding can co-exist!