Causes of Stomach Pain in Pregnant Women Pregnant women often experience stomach ache during pregnancy, which often makes people feel uneasy and anxious. So, what is the cause of stomachache? Let\’s take a look at the possible reasons. 1. Calcium deficiency During pregnancy, the body of pregnant women needs more calcium to support the development of the fetus. Pregnant women are more likely to suffer from abdominal pain if they consume less calcium than they need. In addition, a lack of magnesium in pregnant women may cause muscle spasms, leading to abdominal pain. 2. Reasonable diet. Pregnant women’s eating habits have a great impact on their health during pregnancy.