Ultrasound evaluation of changes in endometrial receptivity from the day of ovulation to the day of transfer in patients with a history of intrauterine adhesions: a prospective cohort study.

Background: High rates of infertility and pregnancy complications in patients with intrauterine adhesion (IUA) even after surgical repair may be associated with poor endometrial receptivity (ER). In our previous study, we found that changes occurred in ER from the day of ovulation to the day of transfer in patients with a normal uterine cavity during natural cycles. However, the changes in ER ultrasound indicators in patients with a history of IUA during natural cycles are unclear, and this study thus aimed to analyze these changes.

Methods: A prospective cohort study of 161 women with a history of IUA who underwent frozen-thawed embryo transfer (FET) was conducted. ER changes from ovulation to the transfer day in the overall, clinically pregnant, and nonpregnant populations were analyzed. Patients were further allocated to the mild IUA or moderate-to-severe IUA subgroup based on the degree of IUA.

Results: Endometrial morphology was mainly type C (a "triple-line" endometrium) on the ovulation day, but type B (an echo of the endometrium similar to that of the surrounding uterine muscle layer) was predominant on the transfer day. From ovulation to the day of transfer in the overall population, there were no statistically significant differences in endometrial blood flow classification or subendometrial volume, but there was an increase in endometrial thickness (9.49±1.89 10.00±2.17 mm; P<0.001) and decreases in other indicators (P<0.05). The changes in the pregnant group were consistent with the direction of changes in the overall population, except for subendometrial volume (9.89±2.33 9.55±2.23 mL; P=0.017), whereas there were no significant differences in the nonpregnant group, except for the frequency of endometrial peristalsis (1.67±1.37 0.49±0.92 times/min; P<0.001). From ovulation to the day of transfer in the moderate-to-severe IUA population, there were significant increases in endometrial thickness (9.01±1.68 9.51±1.99 mm; P=0.002), vascularization index (VI; 1.92±2.58 1.99±3.39; P=0.019), and vascularization flow index (VFI; 0.65±1.18 0.72±1.46; P=0.010), whereas there were decreases in other indicators (P<0.05). From ovulation to the day of transfer in the mild IUA population, there was a significant increase in endometrial thickness (10.04±1.99 10.57±2.23 mm, P=0.011) and decreases in other indicators (P<0.05).

Conclusions: During natural cycles, in patients with a history of IUA, endometrial morphology mainly changed from type C to B, thickness increased, and the volume and frequency of peristalsis decreased. The blood supply of both the endometrium and subendometrium decreased significantly in the pregnant group. These findings provide a better understanding of the changes in ER in such patients, which is helpful for their pretransfer conversation.