Yes, tightening of the stomach can be felt during the first trimester of pregnancy. This is because the uterus is growing and expanding to carry the new life that is starting in a woman’s body. A woman feels this expansion more likely as her stomach begins to tighten.
Aside from this tightening feeling, a woman bearing a growing baby in her experiences pain at the back and sides of the abdomen. The muscles in these areas lengthen and stretch to accommodate the growth of the baby. These changes may bring discomfort to a pregnant woman but these are for a while and to prepare her body to carry comfortably the new life in her.