Hypercalcemia in a calcitriol-treated hypoparathyroid woman during lactation.

We treated a hypoparathyroid woman with calcitriol during pregnancy and did not reduce the dosage after delivery. Despite lactation, the serum calcium level increased to 15.4 mg/dL 11 days postpartum. We treated two other hypoparathyroid women during four pregnancies with either calcitriol or dihydrotachysterol. In all five pregnancies, requirements for the vitamin D preparations increased beginning at the 20-28th week of gestation. Hypercalcemia did not occur in the two women who did not breast-feed and in whom we reduced the dose of calcitriol or dihydrotachysterol after delivery. We conclude the following: 1) Calcitriol is effective for treating hypoparathyroidism during pregnancy; 2) the dose usually needs to be increased during the latter half of gestation; 3) the calcitriol dose should be reduced during lactation; and 4) both mother and infant should be monitored to detect hypercalcemia during breast-feeding. We speculate that low serum estrogen levels associated with breast-feeding promote bone resorption and diminish calcitriol needs in lactating hypoparathyroid women.