Antepartum to postpartum changes in transcapillary fluid balance.

During the puerperium significant changes occur in the body volume homeostasis. In the present study the transcapillary fluid balance was examined antepartum in nine healthy women. The interstitial colloid osmotic pressure was measured by the 'wick' method, and interstitial hydrostatic pressure by the 'wick-in-needle' method in subcutaneous tissue on the thorax and at the ankle. From antepartum (gestational week 37-40) to postpartum (5th day), the following changes were observed: A significant increase in the colloid osmotic pressure both in plasma (mean 1.8 mmHg, P = 0.027) and in the interstitial fluid at the ankle (mean 2.9 mmHg, P = 0.008). Neither colloid osmotic pressure gradient (plasma-interstitium), interstitial hydrostatic pressure, nor haemoglobin and haematocrit changed. The observed rise in the interstitial colloid osmotic pressure must be caused by mobilization of fluid from the interstitium, probably due to a reduced capillary hydrostatic pressure. The increase in plasma colloid osmotic pressure is most likely caused by an increased albumin synthesis and/or transport of interstitial proteins back to the vascular compartment.