The effects of cortisol on the growth rate of the sheep fetus during late gestation

Using indwelling crown-rump length (CRL)-measuring devices, the growth rate of sheep fetuses was monitored during late gestation and after experimental manipulation of fetal plasma cortisol by exogenous infusion and fetal adrenalectomy. In intact control fetuses, the increment in CRL declined progressively during the last 20-25 days of gestation: mean +/- S.E.M. values fell from 5.5 +/- 0.4 mm/day (n = 12) at 21-25 days before delivery to 2.5 +/- 0.3 mm/day (n = 12) in the last 5 days before birth (P 0.05), had a significant effect on the fetal CRL increment measured over 5-day periods during the last 25-30 days of gestation. These findings show that cortisol inhibits growth of the axial skeleton in the sheep fetus during late gestation. They also indicate that the prepartum cortisol surge may be responsible for the normal decline in fetal growth rate observed towards term in this species.