Erythrocyte and erythropoietin responses to hemorrhage in the immature and near term ovine fetus.

OBJECTIVE

Previous reports suggested that immature ovine fetuses have a greater erythropoietin response to hemorrhage than those near term. This study tested the hypothesis that immature ovine fetuses would expand their red cell mass more rapidly than near term fetuses after hemorrhage.

STUDY DESIGN

Chronically catheterized immature ovine fetuses at 109.5 +/- 0.3 (mean +/- SE) days' gestation (term = 150 days) were studied over a 10-day period. They either underwent hemorrhage of 40% of their measured blood volume on day 3 or were in a time control group monitored without hemorrhage. Red cell mass, hematocrit, blood volume, plasma volume, and plasma erythropoietin concentrations were measured at 24- and 48-hour intervals. Responses in the immature fetuses were compared with responses in near term fetuses.

RESULTS

In the control group red cell mass, hematocrit, blood, and plasma volumes increased significantly, whereas plasma erythropoietin concentration decreased significantly with advancing gestational age. In immature fetuses that underwent hemorrhage, the relative changes in red cell mass, hematocrit, and plasma erythropoietin concentration were not significantly different from those seen in the near term fetuses. The only significant posthemorrhage difference was that the increases in blood and plasma volumes were greater in the immature compared with the near term fetuses.

CONCLUSION

Immature and mature fetuses have similar erythrocyte and erythropoietin responses to moderately severe hemorrhage. The larger blood and plasma volume responses in the immature fetuses are consistent with the concept that they have a greater extracellular fluid volume.