If your stomach is tight in early pregnancy, the most common cause is contraction of the uterus, which is often caused by a lack of progesterone, and the smooth muscle of the uterus will contract when there is a lack of progesterone, and you will feel tightness in your stomach. In addition, if you are overly tired or have sexual stimulation in early pregnancy, it may lead to contraction of the uterus. It is recommended to take active rest and, if necessary, go to the hospital to have blood drawn for appropriate tests and give medication according to the results. If your stomach is tight in the early stages of pregnancy, you should also rule out the possibility of ectopic pregnancy and monitor your blood HCG or diagnose it by ultrasound if necessary.