Decreased calcitriol requirement during pregnancy and lactation with a window of increased requirement immediately...

To describe the changes in calcium and calcitriol requirements during pregnancy and lactation in a patient with hypoparathyroidism due to autosomal dominant hypocalcemia.

We summarize the clinical presentation and treatment of the patient and review the pertinent literature.

Calcitriol requirements disappeared during pregnancy in a 34-year-old woman with autosomal dominant hypoparathyroidism secondary to an activating mutation in the calcium-sensing receptor gene. Within hours after delivery, her serum calcium concentration dropped to 4.7 mg/dL (albumin, 3.2 g/dL), and she required intravenous calcium and reinstitution of calcitriol. When lactation began a few days later, her calcitriol requirement again disappeared. As has occasionally been described in the literature, this patient with hypoparathyroidism required no calcitriol during late pregnancy and lactation to maintain a normal serum calcium level.

To our knowledge, this is the first reported case documenting a period of time between pregnancy and lactation when calcitriol requirements reappeared, likely due to a parathyroid hormone-related protein "window" between delivery, when placental production of parathyroid hormone-related protein stops, and lactation, when mammary gland production begins.