Calcium citrate and calcium carbonate can be used by pregnant women, and can be chosen as needed and as prescribed by your doctor. 1. Calcium Citrate and Calcium Carbonate are both calcium supplements, with Calcium Carbonate being cheaper and usually preferred. Calcium carbonate is usually taken with a meal and is more effective. It is not suitable for patients using proton pump inhibitors or histamine H2 receptor antagonists. 2. Calcium citrate is better absorbed when taken on an empty stomach and is generally recommended for patients using proton pump inhibitors or histamine H2 receptor antagonists. Both calcium supplements need to be taken under the guidance of a medical professional, and pregnant women can choose the appropriate one according to their own situation.