Urinary calcium excretion in pregnancy

Urinary calcium excretion and creatinine clearance studies have been conducted in 50 women at 36 weeks of pregnancy and 50 normal controls. Of the pregnant women, 25 had been administered 600,000 IU vitamin D in the 24-26 weeks of pregnancy (supplemented group). The non-supplemented group showed significant hypocalcaemia (even after accounting for low plasma protein levels) and hypocalciuria, while the supplemented group showed normocalcaemia as well as significantly greater 24-hour urinary calcium excretion than the controls. 24-hour creatinine clearance was increased in both groups of pregnant women. It was concluded that, due to increased GFR, urinary calcium excretion tends to increase in pregnancy provided the subject is not deficient in vitamin D. Occurrence of hypocalciuria in pregnancy suggests vitamin D deficiency and should not be considered a physiological adaptation.