Answer: In early pregnancy, the stretching of ligaments is responsible for abdominal tightening. As the baby grows and demands more space, the uterus stretches itself pushing the other organs. Because of this, the stomach becomes hard and tight with each passing day, and you could feel uncomfortable with your stomach being tight. Round ligament pain is fairly common during this phase of pregnancy. This may not be regular though. Besides this constipation, large meals, or flatulence can also lead to abdominal tightening.