What does the uterus feel like when it's stretching?
The uterus is mostly muscle that tends to contract if there’s something in it. This explains why blood clots during a heavy period cause cramping and why labor eventually results when the baby is big enough.
In early pregnancy, the growing baby will expand the uterus, and the result will be contractions against it. Luckily, these contractions are not enough to cause any problems. You may also experience cramping that your health care provider will most likely tell you are “growing pains.” Some cramping is normal—but if you experience any heavy bleeding or times of painful cramping, let your provider know right away.