Challenges and pitfalls in diagnosing and managing severe gestational hypercalcemia

A 38-yr-old primigravida presented at 30 + 2 wk' gestation with pregnancy-induced hypertension and was found to have severe hypercalcaemia (adjusted calcium 3.19 mmol/L). Intravenous fluid therapy produced only transient improvement, and recurrent hypercalcaemia required repeated inpatient management. Parathyroid hormone (PTH) was suppressed, while both 25(OH)D₃ and 1,25(OH)₂D₃ (calcitriol) were elevated. Imaging and laboratory investigations revealed no evidence of malignancy or granulomatous disease. Delivery by elective caesarean section was undertaken at 35 wk' gestation. The neonate developed transient hypocalcaemia with suppressed PTH, requiring brief intravenous calcium supplementation. Maternal hypercalcaemia persisted postpartum, and renal imaging revealed nephrolithiasis and nephrocalcinosis. Serum calcium remained elevated during lactation but normalized after weaning. Extended vitamin D metabolite profiling showed an increased 25(OH)D₃:24,25(OH)₂D₃ ratio, and genetic analysis confirmed compound heterozygous pathogenic variants in CYP24A1, encoding vitamin D 24-hydroxylase, the enzyme responsible for calcitriol degradation. The findings established a diagnosis of gestational hypercalcaemia due to CYP24A1 deficiency. Normal pregnancy is associated with physiological rises in calcitriol, reduced PTH, and hypercalciuria, features that can mimic or mask this disorder. This case illustrates the diagnostic challenges of recognizing CYP24A1 deficiency in pregnancy.