The cause of Braxton Hicks contractions are irregular contractions of the uterus. Braxton Hicks contractions are considered "practice" contractions for the more frequent and painful contractions that occur during true labor. Braxton Hicks contractions are irregular in occurrence and normally painless. These contractions appear unpredictably and sporadically, and can be rhythmic and of mild intensity. In the last month of pregnancy, Braxton Hicks contractions may occur more frequently -- sometimes every 10 to 20 minutes -- and with greater intensity than before.

 

When uterine contractions occur in the third trimester, it is important to distinguish these Braxton Hicks causes from true preterm labor.