During pregnancy, with the passage of time, the fetus body will increase a lot, and at this time the space for activities will become smaller, so the baby will hit the belly in the process of activity, especially the pregnant woman walking in the process of bumps, will lead to fetal stimulation of the uterine wall, the phenomenon of uterine cramps, especially in late pregnancy, the uterus will be more sensitive, once stimulated will produce contractions, there will be a tight, hard stomach This is the time to pay attention to rest and not to overexert yourself. If you feel tightness and hardness in your stomach without severe pain or vaginal bleeding, this is a physiological contraction, which generally does not have any significant impact on the fetus or the pregnant woman.