Practice contraction. Braxton hicks contractions can happen at anytime during your pregnancy. They tend to be milder and more irregular than the contractions you get during labor. In general they are practice contractions that normally occur. If you have contractions more than 4 times in an hour and are preterm, you should call your doctor.
Uterine contractions. Braxton hicks contractions are sporadic uterine contractions that start about 6 weeks into your pregnancy, although you won't be able to feel them that early. You probably won't start to notice them until sometime after mid-pregnancy, if you notice them at all. (some women don't.) they get their name from john braxton hicks, an english doctor who first described them in 1872.