Oestrogens in Fetal and Maternal Fluids Throughout Pregnancy in the Pig and Comparisons with the Ewe and Cow

In order to correlate the concentrations of oestrogens in the fetal fluids of the pig with those observed in the maternal blood and urine, changes in the concentrations of oestrone, oestradiol-17 beta, oestrone sulphate, oestradiol sulphates and oestrone glucuronide were assessed throughout pregnancy in the fetal and maternal fluids. In general, the pattern of change was similar for all oestrogens measured in both fetal and maternal fluids. Since the concentration of oestrogens in allantoic fluid during early pregnancy is reflected in the concentration of these steroids in maternal plasma and excreted in the maternal urine, the rise and fall of oestrogen concentrations around day 30 is suggestive of synthesis followed by a virtual cessation of oestrogen production until the fetus or placenta again produce increasing amounts detectable after day 45. These findings contrast sharply with those in the cow and the ewe where, although similar peaks in oestrogen concentrations are observable in allantoic fluid during early pregnancy, they are not reflected in blood.