I've gotten about a dozen tiny, moles on my chest and breasts during pregnancy, especially around my areolas. I'm really not too concerned about them, though. I really think they're just caused by hormones.
With my first pregnancy I got about 100 new freckles/tiny moles all over chest and stomach. They grew through pregnancy (a tiny bit) but stopped after I gave birth. They're all still there but not very noticeable