Pereira N, et al. - The objective of this study is to investigate the effect of supraphysiologic estradiol (E₂) levels on human placentation in fresh IVF cycles. Supraphysiologic E₂ levels affect early implantation as evidenced by lower placental weights and surface areas, increased fibrin deposition and decidual vasculopathy. These outcomes propose subsequent utero-placental malperfusion, resulting in lower birth weights.