Effects of dexamethasone on the uterine and umbilical vascular beds during basal and hypoxemic conditions in sheep

Objective The purpose of the study was to test the hypotheses that maternal treatment with dexamethasone leads to a reduction in basal umbilical blood flow and diminishes the fetal umbilical hemodynamic response to acute hypoxemic stress in sheep. Study design While under general anesthesia, 23 ewes and their fetuses were instrumented with vascular catheters and transonic blood flow probes around a uterine and umbilical artery at 117 days of gestation (term, approximately 145 days). At 124 days, the ewes were injected intramuscularly with 2 doses of either dexamethasone (12 mg) or saline solution at 24-hour intervals. All animals experienced 2 episodes of hypoxemia during treatment (125±1 days) and after treatment (128±1 days). Results Maternal dexamethasone treatment caused a sustained increase in fetal arterial blood pressure (from 41±3 mm Hg to 45±3 mm Hg) and a transient fall in umbilical vascular conductance (from 6.2±0.9 mL • min−1 • [mm Hg]−1 to 5.4±0.7 mL • min−1 • [mm Hg]−1). During both episodes of hypoxemia, there was a significant increase in umbilical blood flow in the controls, but not in the dexamethasone-treated animals. Conclusion Maternal dexamethasone treatment with doses used in human clinical practice significantly decreased basal umbilical vascular conductance and prevented the normal increase in umbilical blood flow that is induced by acute hypoxemia in fetal sheep.