EXTRACOELOMIC FLUID OSMOMETRY AND ELECTROLYTE-COMPOSITION DURING EARLY GESTATION IN THE BABOON

OBJECTIVE: Access to extracoelomic fluid offers the opportunity to ass ess and potentially treat genetic disorders early in pregnancy. We hav e been using the pregnant baboon as a model to develop techniques and evaluate the feasibility of sampling extracoelomic fluid. The aim of t his study was to determine the osmolality, oncotic pressures, and elec trolyte composition of the baboon's extracoelomic fluid between days 3 9 and 41 of gestation and to compare them with those of maternal blood . STUDY DESIGN: The optimal time to perform the coelocentesis procedur e was determined in 14 timed pregnant baboons. Six coelocenteses were then performed in aseptic conditions. under continuous transvaginal ul trasonographic guidance and avoiding the amniotic or yolk sacs. Betwee n 3 and 5 mL extracoelomic fluid was aspirated from each baboon with a 10-mL syringe. Only 1 attempt at sampling was performed for each of t he 6 animals. Pregnancies were tracked by transabdominal ultrasonograp hic evaluations on postprocedure day 3 and then weekly until day 140 o f pregnancy. Oncotic pressures and biochemical measurements were deter mined with 1 mL extracoelomic fluid and 1 mt heparinized maternal veno us blood. RESULTS: Data analysis suggests that maternal blood and extr acoelomic fluid have similar osmolalities and concentrations of electr olytes but different colloid osmotic pressures (P < .001). CONCLUSION: This nonhuman primate model can be used to gain some insight into the physiologic changes in the composition of the extracoelomic fluid and to evaluate the safety of the coelocentesis procedure. The data sugge st that the chorion laeve behaves as a semipermeable membrane at 40 da ys' gestation.