Plasma solute concentrations during gonadotrophin-induced ovulation

The effects of ovulation induction on some plasma solute concentrations were investigated serially in eleven women, nine of whom conceived in that cycle. Increasing oestrogen output during the follicular phase was associated with decreasing levels of osmolality, urea, total protein and the albumin free protein fraction. Smaller decreases in the concentrations of sodium, potassium, chloride, carbon dioxide combining power (CO2CP) and albumin were not statistically significant. The luteal phase was marked by a rise in osmolality and a fall in CO2CP but no other significant changes. Levels of osmolality, sodium and potassium fell in early pregnancy when oestrogen output was further increased. These results appear consistent with an oestrogen induced expansion of the extracellular fluid compartment by retention of water in excess of solute, which might also account for the similar changes in pregnancy.