Gestational hypercalcemia: Prevalence and biochemical profile

•Population prevalence of gestational hypercalcemia was 1.7 % in the third trimester.•Hyperparathyroidism and vitamin D toxicity were excluded as main causes.•No cases with profiles suggestive of mutations in the CYP24A1 gene were found.•Hypercalcemic women had a relatively high serum 1,25(OH)2D concentration despite an appropriately suppressed PTH. Gestational hypercalcemia is associated with an increased risk of maternal, fetal and neonatal morbidity and mortality. Hypercalcemia may develop during pregnancy in individuals who were previously asymptomatic. The increased sensitivity during pregnancy may be related to physiological, gestational alterations in vitamin D and calcium metabolism and may be influenced by gene variants. The prevalence is unknown. We investigated the prevalence of hypercalcemia in trimester 3 (T3) in a population representative prospective cohort study (n = 1832) in South-West Sweden. Women with serum albumin (Alb) adjusted calcium (CaAlb) ≥ 2.65 mmol/L in T3 (n = 30) were matched to normo-calcemic controls, and markers of calcium and vitamin D metabolism were investigated in trimester 1 (T1) and T3. Serum concentrations of Ca, phosphate (P), Magnesium (Mg), Alb and creatinine (Cr), parathyroid hormone (PTH; T3 only), vitamin D metabolites (total 25(OH)D, 1,25(OH)2D, 24,25(OH)2D, and free 25(OH)D) were analysed in T1 and T3. CaAlb (Payne; inter-laboratory difference: UEA = 0.15 + 0.9*UGOT; UEA 2.54 = UGOT 2.65) and estimated glomerular filtration rate (eGFR; modified 4-variable MDRD) and vitamin D metabolites ratios (VMR) were calculated. Normally and non-normally distributed data were presented as mean (SD) or median (95 %CI). Group differences in relationships between vitamin D metabolites and with PTH were investigated with multiple regression analyses. Hypercalcemia in T3 was found in 1.7 % of women. PTH concentrations suggestive of primary hyperparathyroidism was found in 1 woman and none had 25(OH)D or 24,25(OH)2D concentrations in the toxicity range or suggestive of mutations in the CYP24A1 gene. CaAlb was significantly higher in hypercalcemic cases compared to controls in T1 (2.44 (2.30–2.80) vs 2.37 (2.25–2.49) mmol/L) and T3 (2.63 (2.52–2.78) vs 2.46 (2.31–2.58) mmol/L). Serum P was higher among cases than controls in T3 (1.12 (0.16) vs 1.07 (0.18) mmol/L) but not in T1 (1.12 (0.18) and 1.12 (0.16) mmol/L). PTH in T3 was lower in cases (1.6 (1.6–2.8) vs 2.3 (2.1–2.8) pmol/L) but 1,25(OH)2D concentrations were similar. Th