There are several reasons for the hardness of the belly in the second trimester: first, fetal movement, the form of fetal movement is different for each pregnant woman, but sometimes a hard bag is found on the belly, which may be the result of the fetus moving inside the belly and appearing. Second, it may be caused by other reasons, such as eating bad stomach or stomach cold, and caused by the increase in abdominal pressure of pregnant women caused by the stomach hard. Third, the most common cause is the physiological contractions of pregnant women, because in the late embryonic development into a fetus and fetal growth, the pregnant woman’s uterine muscle and abdominal wall muscles will be stretched, which will lead to a tight or hard stomach. Another reason for physiological contractions may be related to the amplitude of fetal movement, when the fetus moves more, it may cause physiological contractions in pregnant women, resulting in a hard stomach.