Progesterone concentrations in maternal and foetal blood plasma of ewes

In pregnant ewes the progesterone concentrations in plasma from the maternal jugular, ovarian (active ovary) and uterine veins and from the foetal umbilical vein were measured by a competitive protein-binding technique.

Peripheral plasma levels remained fairly uniform throughout pregnancy, whereas ovarian levels dropped at about the 130th day of pregnancy. Uterine plasma levels were low until the 80th day; foetal levels rose as pregnancy progressed.

The major sources of progesterone appeared to be the ovary (corpus luteum) and the uterus (placenta). The ovarian contribution was greater during the first two-thirds of pregnancy than later, whereas that made by the placenta was lower during the first one-third of pregnancy.