As early as 8 weeks gestation, the uterus begins to generate small waves of contractions. These are called Braxton-Hicks contractions. Most women describe them as a tightening or hardening but not painful. They often notice them when exercising, stretching (e.g. when doing Yoga), lifting, or when having sex (especially noticeable with an orgasm!). Early on in pregnancy lots of women don’t notice them, but commonly will be aware of them in second half of pregnancy, and some women will describe them as very uncomfortable. They certainly seem to increase in the last couple of weeks of pregnancy and is a common time for women to misinterpret them as the ‘real thing’. They are much more evident in 2nd and subsequent pregnancies.