Plasma progestagens and oestrogens in fetus and mother in late pregnancy.

This research studied hormone levels in pregnant horses and their fetuses towards the end of pregnancy, finding significant variations in estrogen and progestagen concentrations, which may have implications for understanding the metabolic cycle in the fetus and hormone changes around birth.

Research Subjects and Purpose

• The research was conducted on normal Thoroughbred and catheterized Pony mares along with their fetuses.
• The main purpose of the study was to examine fetal estrogen and progestagen concentrations in late gestation and compare these with maternal values.

Key Findings

• Fetal hormone concentrations of estrogen and progestagens in late gestation were significantly higher than maternal values.
• Specifically, there was a large venous-arterial difference in progestagens and total estrogens throughout late gestation in the umbilical steroid concentrations.
• This significant difference potentially indicates a metabolic cycle in the fetus between progesterone and other steroid metabolites.
• High concentrations of metabolites of 20alpha-dihydroprogesterone were discovered in both maternal and fetal plasma.

Variations in Hormone Levels towards Parturition

• In the breed Thoroughbreds, and to a lesser extent in Pony mares, plasma progestagens increased towards birth, while total plasma estrogen decreased.
• The only estrogen which showed an increase in concentration near term was oestradiol-17beta.

Observation before Parturition

• In one pony mare and her fetus, there was a noticeable drop in fetal plasma progestagen 24 to 36 hours before parturition, even though maternal peripheral progestagen concentrations remained high.