Urinary excretion of calcium in late pregnancy and its relation to creatinine clearance.

The distribution of the values for the daily urinary excretion of calcium during the last trimester of pregnancy was skewed toward high values in 1,034 women in Bradford, England. The logarithms of the values had a Gaussian distribution. The 95% range of this log-Gaussian distribution was 0.75 to 15.5 mmoles (30 to 620 mg.) per day. Nearly 20% of the values exceeded 8.75 mmoles (350 mg.) per day, which is the reported upper limit of the 95% range for nonpregnant women. Creatinine clearance is known to increase during pregnancy, and a prospective investigation in 112 pregnant Caucasian women in a hospital showed a highly significant correlation between calcium excretion and creatinine clearance. It is suggested that the increase in calcium excretion during pregnancy is due to the increase in glomerular filtration rate.