Pregnancy proteins in the endometrium after follicle aspiration for in vitro fertilization

Placental proteins PP10, PP12, and PP14 and pregnancy-associated plasma protein A (PAPP-A) and relaxin (RX) were studied by the immunoperoxidase method in the uterine mucosa at the time of embryo replacement in 18 women for whom no embryo was available to be replaced. All subjects had received 17 alpha-hydroxyprogesterone caproate at the time of follicle aspiration, which had been performed 36 hours after preovulatory administration of hCG. The time between follicle aspiration and endometrial biopsy varied from 26 to 216 hours. PP10 was not detected in any specimen. RX was found in 17 of 18, PP12 in 15 of 18, PAPP-A in 14 of 18, and PP14 in 6 of 18 specimens. In a normal cycle, PP12, PAPP-A and RX appear in the endometrium on the fourth day post ovulation. In the conditions described above the same proteins could be seen in the endometrium sooner after oocyte retrieval. This may be due to a strong progesterone effect after multiple follicle aspirations and treatment with 17 alpha-hydroxyprogesterone. The significance of the occurrence of these pregnancy proteins as well as that of the morphologic and biochemical maturity of the endometrium at the time of embryo transfer are discussed.