Pregnant women taking any calcium tablets may be constipated, which is a common side effect of calcium supplements. Constipation is a common adverse reaction to calcium supplements. The main ingredient of calcium tablets is calcium carbonate, and the main ingredients of various brands are similar, so there is no guarantee that any calcium tablet will not cause constipation. Routinely used calcium tablets are calcium carbonate, which may dissolve in stomach acid to form calcium chloride, which forms calcium phosphate in the intestinal fluids that can be deposited on the feces, leading to the occurrence of constipation. Supplementing calcium tablets during pregnancy with fiber, proper exercise, and good bowel habits may improve constipation. Calcium supplements as well as other medications during pregnancy should be used under a doctor’s supervision.