A progestagen-dependent endometrial protein in human amniotic fluid.

A protein was detected in human amniotic fluid that had properties identical to those of the progestagen-dependent endometrial protein. The concentration of the amniotic fluid protein was maximal during Weeks 15-18 of pregnancy and then declined rapidly. The protein was not detected in immature and mature placentae, ovary, Fallopian tube, myometrium and cervix. We conclude that a specific protein synthesized by the human uterine decidua is transported to the amniotic sac.