Patterns of sex hormone receptor expression in stimulated endometrium from oocyte donors

In patients with high serum E₂ embryo transfer is often postponed, as high E₂ levels adversely affect embryo transfer outcome. We aimed to determine if stratified serum oestradiol (E₂) and progesterone (P₄) levels differentially affect endometrial histology and endometrial oestrogen and progesterone receptor protein levels. Endometrial biopsies were collected from oocyte donors. Samples were divided based on peak serum E₂ levels into three groups: (i) low-E₂ (n = 33) E₂≤2999pg/mL; (ii) mid-E₂ (n = 40) E₂ 3000-4999 pg/mL; and (iii) high-E₂ (n = 15) E₂≥5000 pg/mL. Oestrogen receptor alpha (ERα) and progesterone receptors A and B (PR) protein levels in endometrial stroma (S), glandular (GE) and luminal (LE) epithelia were assessed by immunohistochemistry. Samples in high-E₂ group demonstrated strongest association with accelerated endometrial maturation (2 (1-2); 2 (1-3); and 3 (2.8-3) median days of advancement of endometrial maturation respectively in low, mid, high-E₂ groups, p = 0.046). There were significant differences in ERα and PR immunoexpression in S, GE and LE among the groups (p < 0.05). Higher E₂ levels were associated with decreased ERα expression (p < 0.017) in GE and LE, and increased PR expression in S and GE (p < 0.011 and p < 0.0001, respectively). Higher serum E₂ levels were associated with impaired endometrial steroid hormone receptor expression, higher serum P₄ and more advancement of endometrial maturation.