Sex-specific differences in the concentration of tubular parameters in the amniotic fluid of second trimester fetuses

Renal dysplasia and obstructive uropathy are more common in males and are associated with an increased tubular loss of electrolytes. We aimed to compare the midtrimester concentration of tubular parameters in the prenatal period between healthy male and female fetuses.

Amniotic fluid was collected at 16 weeks of gestation at the time of genetic amniocentesis. The concentration of sodium, chloride, potassium, calcium, phosphate, magnesium, α1-microglobulin, creatinine and urea was determined in the amniotic fluid of 92 male and 108 female fetuses.

The concentration of sodium, chloride and calcium was not significantly higher in male than in female fetuses. In contrast, the concentration of potassium (p=0.01), phosphate (p=0.04), magnesium (p=0.04) and α1-microglobulin (p=0.04) was significantly increased in the amniotic fluid of male fetuses. The concentration of electrolytes correlated to the concentration of creatinine, urea and α1-microglobulin.

The concentration of specific tubular parameters in the amniotic fluid was higher in male compared with female fetuses. Whether this might point to sex-specific differences in tubular function in second trimester fetuses or reflect glomerular filtration or other interfering factors remains speculative.