Well, me and my boyfriend have sex ALOT and I'm pregnant now, he drinks my breast milk, and I haven't seen him get sick or anything. But, it depends I guess. How much bigger have her breasts gotten? And how many months is she pregnant. Because I went from a cup size 36B to a 32C...and he STILL sucks my nipples. haha, and also, it feels good. so if she's okay with it, go ahead. it'll make her feel wanted and happy (: it makes me that way all the time!!!