Serum calcium and parathormone during normal pregnancy in Malay women

To ascertain the calcium status in normal pregnant Malay women.

In a cross-sectional study, serum parathormone (PTH) and calcium concentrations, and 24-h urinary calcium excretion were estimated in age-matched normotensive pregnant women, over the 3 trimesters.

No statistically significant differences were evident in serum ionised calcium concentrations between the pregnant women in the 3 trimesters. Serum total calcium however, was significantly lower in women in the 3rd trimester of pregnancy (2.29+/-0.16, 2.26+/-0.13, and 2.16+/-0.12 mmol l(-1) in the 1st, 2nd, and 3rd trimesters, respectively; P < 0.001). Serum parathyroid hormone concentration was significantly higher in the 3rd trimester of pregnancy (3.37+/-3.31, 4.36+/-4.55, and 7.17+/-6.6 pg ml(-1) in the 1st, 2nd, and 3rd trimesters, respectively; P < 0.05). No significant differences were evident in serum sodium and potassium concentrations between the 3 groups. Urinary calcium excretion was significantly lower in women in the 3rd trimester of pregnancy (3.41+/-1.80, 3.56+/-3.31, and 2.46+/-1.71 mmol day(-1) in the 1st, 2nd, and in the 3rd trimesters, respectively; P < 0.05). No significant differences were evident in urine output, creatinine clearance, or in the excretion of sodium and potassium between the 3 groups.

It appears that a significant fall in serum total calcium occurs in the 2nd half of normal human pregnancy when there is also an increased fetal demand and perhaps also a relatively insufficient maternal intake and/or intestinal absorption. The lower urinary calcium excretion probably occurs secondary to this and may suggest a fall in total body calcium and an attempt by the body to conserve calcium. While under normal circumstances, this level of fall in total calcium may not be significant, the coincidence of occurrence of hypertensive disorders of pregnancy during this stage of pregnancy, and the evident link between low calcium intake and pregnancy-induced hypertension (PIH) and its possible amelioration with calcium supplementation, suggests a need to assess calcium status in pregnant women with a view to providing calcium supplementation during pregnancy.