Hi mama! Congrats sa pregnancy! Usually OBs start prescribing calcium around second trimester (weeks 13-14 onwards), so it's perfect timing to ask your doctor about it sa next checkup, bawat OB may sariling approach kasi depending sa diet at needs mo. One of my mum friends took hers starting week 16, pero iba-iba talaga, so best mag-confirm lang with your OB para sure sa dosage at timing perfect for you!