Electrical potential difference between exocelomic fluid and maternal blood in early pregnancy

The forces that drive transfer of solutes between maternal blood and embryo in early human pregnancy are poorly understood. The aim of this study was to determine whether there is an electrical potential difference (PD) between maternal blood and the exocelomic cavity and between maternal blood and the amniotic cavity in the normal human conceptus at or before 10 wk of pregnancy. We measured PD between a saline-filled catheter in a forearm vein of women undergoing termination of pregnancy for psychological reasons in the first trimester and a second saline-filled catheter in the exocelomic cavity or amniotic cavity of their conceptus. The mean (+/- SE) maternal blood/exocelomic cavity PD in eight women was 8.7 +/- 1.0 mV and the mean maternal blood/amniotic cavity PD in four of the women was 6.7 +/- 1.3 mV, embryo side negative for both sets of measurement. These data show that there is a PD between maternal and embryonic extracellular fluid in the first trimester that will directly influence exchange of ions between the two compartments.