Maintenance of serum calcium by parathyroid hormone-related peptide duringlactation in a hypoparathyroid patient

We describe the changes in calcium homeostasis seen in a hypoparathyroid wo man during the third trimester and with lactation following her second preg nancy. During lactation her need for sup supplemental calcium and calcitrio l abated, and in fact she was transiently hypercalcemic and hypophosphatemi c. This change was associated with a rise of serum parathyroid hormone-rela ted peptide (PTHrP) released systemically during lactation. This is the fir st documentation of the time course of serum PTHrP levels from the late thi rd trimester throughout lactation in a hypoparathyroid woman. In this conte xt PTHrP may have sufficient biological activity to compensate for parathyr oid hormone deficiency.