Braxton hicks can happen anytime at 2nd trimester onwards and it is totally normal. As long as it is not painful like contractions. But...... I had frequent braxton hicks starting on my 2nd trimester & it gets more and more frequent on my 3rd trimester. Only to find out that I was actually having contractions. So if it is very constant, very frequent and very uncomfortable, do let your gynae know.
Some women experience that at 6 months. this is the uterus's way of practicing for labor
Thanks!
Yantie Ashanty