An Israeli study suggested that pregnant women with primary hyperparathyroidism had only mildly elevated serum calcium levels, and there was no increased risk of obstetrical complications.[8] A register-based cohort study from Denmark also demonstrated that a diagnosis of primary hyperparathyroidism did not increase the rate of abortions.[9] A plausible explanation is that parathyroid tumors had the expression of functional estrogen receptor (ER)-β but not ER-α.[10] Furthermore, expansion of the intravascular volume and fall in serum albumin levels may mask hypercalcemia in pregnancy.[11]. This evidence concerns the gene ESR1 and hypercalcemia disease.