Objective: Little is known of the hormone environment of the developing early human embryo. We have therefore measured selected steroids in the intrauterine fluids of early pregnancy.
Design: Measurement of progesterone, 17 alpha-hydroxyprogesterone, oestradiol-17 beta, testosterone, androstenedione, cortisol and dehydroepiandrosterone sulphate in matched samples of coelomic fluid, amniotic fluid and maternal serum collected before pregnancy termination from 12 women between 8 and 12 weeks gestation.
Results: Mean concentrations of progesterone, oestradiol-17 beta and 17 alpha-hydroxyprogesterone in coelomic fluid were respectively 20, 6 and 2 times greater than in maternal serum and 8, 13 and 2.6 times those in amniotic fluid. Concentrations of testosterone and androstenedione were highest in maternal serum and lowest in amniotic fluid. Cortisol and dehydroepiandrosterone sulphate were found in intrauterine fluids only at the limit of detection but in normal concentrations in maternal serum.
Conclusions: Coelomic fluid contains relatively high concentrations of progesterone, oestradiol-17 beta and 17 alpha-hydroxyprogesterone which may be synthesized locally. Amniotic fluid contains lower concentrations of steroids (other than progesterone) than are found in coelomic fluid or maternal serum. Free diffusion of steroids across the amnion appears limited. This may constitute a mechanism to protect the embryo from unwanted exposure to biologically active steroids.