A discordant movement in urine calcium excretion in relation to serum calcium and parathyroid function occurring immediately after birth.
We studied the relationship between serum calcium and urinary calcium excretion in association with the parathyroid function in 28 neonates at birth and at five days of age. At birth, the urine calcium was low in spite of high cord serum calcium and a low parathyroid hormone level. On the fifth day of birth, urinary calcium excretion increased despite the reduction in serum calcium and an increase in the parathyroid hormone. These results suggest that the large increase in renal blood flow and the consequent increase in calcium load on the immature renal tubule occurring after birth may be the main cause for the change in this serum calcium-urinary calcium relationship. This finding can in part explain the temporary hypocalcemia during this period.