Transcapillary fluid dynamics during ovarian stimulation for in vitro fertilization

Transcapillary fluid dynamics were studied in 10 women during ovarian stimulation for in vitro fertilization. The examinations were done on the first day of stimulation (day 3 of the menstrual cycle, mean serum estradiol concentration 0.2 nmol/L), and the day before oocyte aspiration (day 10 to 12, mean serum estradiol concentration 6.8 nmol/L). Interstitial colloid osmotic pressure was measured on the thorax at heart level by the "wick" method, and interstitial hydrostatic pressure by the "wick-in-needle" method. Plasma colloid osmotic pressure decreased (mean, 2.0 mm Hg; p less than 0.002) and interstitial colloid osmotic pressure increased (mean, 1.0 mm Hg; p less than 0.02) during hormonal stimulation. This implies a reduced transcapillary colloid osmotic gradient (plasma colloid osmotic pressure--interstitial colloid osmotic pressure), probably because of increased capillary permeability to plasma proteins. Hemoglobin and hematocrit were significantly reduced, and body weight and foot volume significantly increased. These results demonstrate that during ovarian stimulation there are both water retention and augmented filtration of fluid from the vascular to the interstitial compartment. This may be of significance for the pathophysiologic condition in the ovarian hyperstimulation syndrome.