Oestrogen and progesterone concentrations in peripheral blood in pregnant red foxes (Vulpes vulpes)

Oestrogen levels were low during most of gestation, but there was a significant increase (P less than 0.05) in oestradiol concentrations at implantation. Early pregnancy was characterized by high levels of progesterone which decreased significantly (P less than 0.001) thereafter, but there was no decline in progesterone or rise in oestrogen levels at parturition. There was no difference in the length of progesterone secretion between pregnant and non-pregnant females.