Aim To analyze the effects of high ovarian response on endometrial collagen synthesis and related gene expression during the peri‐implantation period in patients undergoing in vitro fertilization‐embryo transfer. Methods Peripheral blood and endometrial biopsies were obtained from infertile women on day 6 after oocytes retrieval or ovulation in 16 stimulated cycles (SC) and 16 natural cycles (NC) respectively. Serum estrogen (E2), progesterone (P4), histological staging, endometrial collagen, matrix metalloproteinases (MMP2, 9) and tissue inhibitors of metalloproteinases (TIMP1, 3) were assayed. Results Serum levels of both E2 and P4 were significantly higher in the SC group than those in the NC group. All endometrial samples were in the secretory phase. The collagen in the stroma of the SC group was more dense and higher than that in the NC group. MMP2 and MMP9 were detected significantly lower in the SC group than those in the NC group, while TIMP1 and TIMP3 were significantly higher. MMP2, 9 expressions are increased by estrogen and reduced by progesterone in dose‐dependent manner through estrogen receptor and progesterone receptor. Correspondingly, TIMP1, 3 expressions decreased by estrogen dose‐dependently while progesterone played the opposite role. Conclusion High levels of P4 could stimulate excessive synthesis of collagen in peri‐implantation endometrium of women with high ovarian response, and the mechanisms may be related to the decrease of MMP2, 9 and the increase of TIMP1, 3 through P4 receptor.

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