Contractions that are intermittent “practice” contractions of the uterus are Braxton Hicks Contractions that can start very early in pregnancy, possibly as early as 6 weeks along. Most women don’t begin to notice them until the second trimester, closer to 20-24 weeks. Sometimes these painless uterine contractions go undetected until the third trimester (this is when they’re the most common) and sometimes women may never experience any. It seems they are felt earlier and with greater intensity in second or subsequent pregnancies.