Emergency contraception alters progesterone-associated endometrial protein in serum and uterine luminal fluid

To evaluate the effect of high-dose oral contraceptives on serum and uterine luminal fluid progesterone-associated endometrial protein in the luteal phase.

Five ovulatory women participated in the study. In a control cycle, serum and uterine lavage samples were collected on luteal day 11. In the next cycle, on luteal day 9, the participants were given two 50-micrograms ethinyl estradiol-norgestrel tablets, repeated 12 hours later. Serum and uterine lavage samples were collected 48 hours (luteal day 11) after the last dose and analyzed by two-dimensional polyacrylamide gel electrophoresis and radioimmunoassays of the serum.

Progesterone-associated endometrial protein levels were lower in sera from treated compared with control cycles. Analysis of serum levels of this protein by two-dimensional polyacrylamide gel electrophoresis did not reveal bands corresponding to the known size and charge characteristics (27 kd and pI of 4.9) in either control or treatment samples. On the other hand, in uterine lavage samples, a complete suppression of the 27-kd, pI-4.9 species was evident after treatment.

High-dose ethinyl estradiol-norgestrel emergency contraception effectively suppresses progesterone-associated endometrial protein in the midluteal uterus, potentially altering the endometrial environment unfavorably and affecting the survival of the early embryo.