We have shown that 7 days of UtBF reduction in sheep results in a 38% decrease in fetal linear growth rate (LGR) from 6 mm/day to 3.7 mm/day (Am J Physiol, 1996). This decrease in LGR correlates with the fetal concentrations of oxygen and glucose. Subsequent studies, in which fetal PaO2 was increased by providing supplemental oxygen to the ewe during UtBF reduction, failed to prevent the development of fetal growth restriction. The present study was undertaken to test the hypothesis that fetal growth restriction might be prevented by providing supplemental O2 and glucose during UtBF reduction. Six sheep with singleton pregnancies at 115-117 days gestation were prepared with vascular catheters, a fetal crown-rump length measuring device, a vascular occluder on the maternal terminal aorta, and a catheter in the maternal trachea. Fetal LGR was measured daily after surgery. The sheep were recovered for 8-14 days after which serial studies were performed 7 days apart. Following a basal study UtBF was reduced and sheep were supplemented with 100% O2 at 2-2.5 lpm via the maternal tracheal catheter. In addition, a variable glucose infusion was begun through the middle uterine artery with the goal of increasing the fetal arterial glucose concentration by 25-50%. UtBF reduction and O2 and glucose concentrations were checked twice daily between the Basal and Day 7 studies.

Results: In the following table data are shown as mean±SEM; A, maternal artery; a, fetal artery; *p < 0.05 by paired t-test. There were no significant changes in fetal LGR; in fetal insulin, lactate, pH, or PCO2 levels; nor in umbilical glucose or oxygen uptake between the Basal and Day 7 studies.

Table 1 No caption available.
Full size table

Conclusions: Supplemental O2 and glucose can be provided chronically to the fetus via the maternal circulation. Provision of these during 7 days of UtBF reduction prevents growth restriction in this fetal lamb model of placental insufficiency.