Scanning electron microscopy of human preimplantation endometrium in normal and clomiphene/human chorionic gonadotropin-stimulated cycles

Embryo transfer after in vitro fertilization of oocytes obtained from unstimulated or stimulated women is usually carried out earlier than when an embryo developed in vivo reaches the womb. The possible asynchrony between the developmental stage of the embryo and that of the endometrium at transfer might reduce the prospects for implantation; so also might any secondary effect of stimulation. Preimplantation endometrium dated by plasma hormone analyses of 17β-estradiol and progesterone in five unstimulated and eight stimulated women was surveyed. Three features were examined, namely, the frequency, distribution, and appearance of ciliated cells, nonciliated cells, and apical protrusion. Wide regional variations were observed, but no continuous or consistent changes or differences were found from ovulation to the time for implantation in unstimulated and stimulated cycles. Therefore, from the morphologic point of view, the surface might be ready to accept a transferred embryo at any time within a range of days after ovulation.