Introduction: Primary hyperparathyroidism (PHPT) in pregnancy is rare but associated with significant maternal and fetal risks.
Clinical case: A 25 yo female, G2P0, was referred with hypercalcaemia at 22 weeks’ gestation. She was diagnosed with hypertension and nephrotic-range proteinuria earlier in the pregnancy. Corrected calcium was elevated 2.9 mmol/L with non-suppressed parathyroid hormone (PTH) 4.7 pmol/L. Vitamin D was 47 nmol/L. Urinary fractional excretion of calcium was unexpectedly low at 0.85%. Calcium levels in 3 first degree relatives were normal and genetic testing for genes implicated in MEN and familial hypocalciuria hypocalcaemia (FHH) were negative. Thyroid imaging suggested an inferior adenoma which, when biopsied, had elevated PTH levels on saline washout. A diagnosis of primary hyperparathyroidism was made and she proceeded to minimally invasive parathyroidectomy at 29 weeks gestation. Parathyroid adenoma was confirmed histologically. She is now 31 weeks gestation and remains normocalcaemic.
This case highlights the diagnostic challenges associated with hypercalcaemia in pregnancy. Pregnancy hormones drive an increase in calcitriol, which in turn leads to increased intestinal calcium absorption. The fetal calcium requirements are predominantly in the 3rd trimester, thus to prevent hypercalcaemia prior there is normally a compensatory increase in urinary calcium excretion.
Hyperparathyroidism is linked with increased maternal and fetal complications in particular hyperemesis, pre-eclampsia, nephrolithiasis and pancreatitis in the mother, and fetal growth restriction, neonatal hypocalcaemia and tetany in the infant due to chronic hypercalcaemia suppressing the fetal parathyroid.
Adequate hydration with close monitoring is required for all patients, with the gold standard remaining parathyroidectomy in the second trimester for moderate to severe cases.
Conclusion: Although rare, hypercalcaemia in pregnancy presents as a diagnostic challenge due to the normal physiological changes that occur. Correct diagnosis is important to allow appropriate and timely surgery for those with PHPT to reduce the associated risks.