Characterization of endometrial growth in proliferative and early luteal phase in IVF cycles

Human endometrium has a definite role in implantation, although knowledge about its modifications in the course of IVF cycles is still limited. This study was performed to characterize endometrial growth throughout stimulation treatment in women undergoing IVF cycles, regardless of clinical outcomes. Endometrial growth was longitudinally evaluated by ultrasonography in the first induced ovarian stimulation cycle (717 patients). Acceleration and length of significant growth were used to assess the slope of the growth curve mathematically. Endometrial growth showed a parabolic trend and final thickness was significantly affected by age (P < 0.01). Endometria that tended to overgrowth had a more rapid and longer growth during the whole phase. A similar stimulation treatment was repeated within 6 months of the first one and a second evaluation was carried out to verify whether similar growth occurred. Similar growth was observed in 76% of the patients, with an absolute difference between the two cycles of <4 mm in 84% of cases. The endometrium seems to have an individual intrinsic potential that can be expressed regardless of the stimulation protocol. This supports the hypothesis that individual factors (intrinsic properties of the endometrium) significantly affect endometrial growth.