Urinary calcium and magnesium excretion relates to increase in blood pressure during pregnancy

Pregnancy-induced hypertension and preeclampsia are serious clinical manifestations during late pregnancy and the cause for increased maternal and foetal morbidity and mortality. The pathogenesis is unknown but experience from treatment schemes suggests that minerals may be of importance. Mineral homeostasis is influenced by acid-base conditions. The aim of the study was to elucidate the relation between acid-base balance, urinary mineral excretion and blood pressure during pregnancy.

A prospective observational study of a general population.

The study was performed at the Midwife Health Center in Borås, Sweden, where practically all pregnant subjects in the catchment area are registered. First time pregnant subjects (n = 123) were voluntarily recruited without exclusion criteria. A 24 h urine sample was collected at pregnancy week 12 and analyzed for creatinine, calcium, magnesium, and urea as a proxy for acid conditions. Blood pressure was recorded every 2-3 weeks until delivery.

There was a relation between the excretion of urea and calcium and magnesium at week 12. A blood pressure increase was found after pregnancy week 30 but only among subjects who had a high excretion of calcium and magnesium at week 12.

If an increase in blood pressure during the later part of pregnancy a risk indicator for preeclampsia, the results suggest that an excessive secretion of calcium leading to a functional deficit might be a risk indicator for gestational hypertension and preeclampsia. Intervention experiments are required to assess this hypothesis.