Restoration of Fetal Red Blood Cells and Plasma Proteins After a Moderately Severe Hemorrhage in the Ovine Fetus

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Abstract

OBJECTIVE

We hypothesized that the fetus, in response to a moderately severe hemorrhage, would restore its plasma volume and red blood cells so that plasma volume would be returned to normal within 24 hours and red blood cell mass would be restored in 5 to 7 days.

STUDY DESIGN

Time-dated pregnant sheep (five control and six hemorrhage, gestational age 124 +/-1 (SE) days) were subjected to a 10-day protocol. Fetal blood volume, plasma volume, red blood cell mass, and plasma protein mass were measured on protocol days 1, 3, 4, 6, 8, and 10. Fetal plasma erythropoietin and plasma iron concentrations were measured daily. On protocol day 3 the hemorrhage animals underwent a 120 ml fetal hemorrhage over 2 hours. Statistical analysis was by three-factor analysis of variance.

RESULTS

Control animals had a progressive increase in blood volume, plasma volume, plasma protein mass, and red blood cell mass throughout the 10-day protocol. The 2-hour hemorrhage removed 39.8% +/-1.2% of the prehemorrhage blood volume. During the 7-day posthemorrhage recovery period fetal blood volume and red blood cell mass in the animals that were hemorrhaged expanded in parallel to, but remained below, that of the control animals. There was no difference in the expansion of fetal plasma volume or plasma protein mass between the two groups. After hemorrhage there was a nonsignificant increase in the fetal reticuloycte index in the animals undergoing hemorrhage. In response to the hemorrhage, erythropoietin levels increased and remained marginally elevated, whereas plasma iron levels decreased in the hemorrhaged animals relative to controls during the 7-day recovery period.

CONCLUSIONS

The normal expansion of plasma volume and plasma protein mass that occurs with fetal growth was not altered by a large fetal blood loss. However, in spite of a transient increase in plasma erythropoietin levels the fetuses undergoing hemorrhage did not restore their red blood cell mass or blood volume. These observations suggest that the ovine fetus is able to withstand a significant loss of red blood cells, but fetal transfusion may be needed to restore fetal red blood cell mass after a moderate-to-severe fetal hemorrhage. (AM J OBSTET GYNECOL 1993;169:1472-8.)

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