Letrozole versus artificial hormonal endometrial preparation for vitrified–warmed embryos transfer cycles

Improved Pregnancy Outcomes and Endometrial Receptivity by Thawed Frozen Embryo Transfer in Mildly Stimulated Cycles with Letrozole Combined with Estrogen in Women with Unresponsive Thin Endometrium Compared to Standard Endometrial Preparation with Estrogen Alone: A Retrospective Study

Context

Infertile women undergoing frozen embryo transfer (FET) cycles may not show optimal endometrial growth with estrogens alone.

Aim

To evaluate clinical effect of mild stimulation with letrozole and estrogens on endometrial growth in comparison to standard endometrial preparation with oral and topical estrogens in infertile women with unresponsive thin endometrium undergoing FET.

Settings and design

Retrospective observational case-control study.

Material and methods

Forty women unresponsive to first AC-FET cycle were given mild stimulation with letrozole and estrogens as second LE-FET cycle for endometrial preparation (LE-FET study group) and compared with 40 historical controls who had received two cycles of AC-FET (AC-FET control group). Responses were assessed by optimal endometrial thickness (≥ 7 mm) and clinical pregnancy.

Statistical analysis

Descriptive statistics were elaborated by mean ± SD and percentages. Results were expressed by mean ± SD, unpaired t test for difference in endometrial thickness, chi square and Fisher exact test to compare the difference in pregnancy among both groups.

Results

Mean endometrial thickness was significantly increased in LE-FET study group (6.68 ± 2.09 mm) versus AC-FET control group (5.35 ± 1.90 mm). Higher clinical pregnancy rate was noted in study group as compared to control group (35% versus 12.5%).

Conclusion

This study suggests that letrozole with estradiol (LE-FET) compared to estradiol alone (AC-FET) for second cycle significantly increased endometrial thickness and improved clinical pregnancy rates in women with unresponsive thin endometrium after first AC-FET cycle with estradiol alone. Addition of letrozole to estrogen upfront for FET cycles may enhance endometrial receptivity and might improve pregnancy outcomes.

The effect of letrozole versus artificial hormonal endometrial preparation on pregnancy outcome after frozen-thawed embryos transfer cycles: a randomized clinical trial

BACKGROUND

Considering that clinical trial studies are limited in polycystic ovary syndrome (PCOS) patients, and there is no consensus on an optimum endometrial preparation protocol for frozen embryo transfer (FET), the present study was designed as a randomized clinical trial to compare the reproductive outcomes following stimulated cycles with letrozole plus human menopausal gonadotropin (HMG) for endometrial preparation compared with routine AC-FET.

METHODS

This randomized controlled trial was carried out on infertile PCOS patients who underwent IVF/ICSI and FET cycles in Arash Women's Hospital affiliated to Tehran University of Medical Sciences between September 2018 and January 2020. PCOS diagnosis was based on the Rotterdam criteria. Eligible patients were randomly allocated into two groups: stimulated cycle with letrozole plus (HMG) (intervention group) and routine artificial hormonal endometrial preparation (control group).

RESULTS

One hundred seventy-seven infertile patients were recruited for participation in the study. Of these, 57 women were excluded due to non-eligibility for entering the study, and a total of 120 patients were randomly assigned to two study groups. After follow up, the cycle outcomes of 57 patients in the intervention group and 59 patients in the control group were compared. The data analysis showed that the two groups did not have significant differences in fundamental and demographic characteristics. After the intervention, there were no significant differences in implantation rate, chemical, ectopic, and clinical pregnancy rates between groups. Moreover, the rates of miscarriage and ongoing pregnancy were similar between groups (P > 0.05).

CONCLUSIONS

We found similar pregnancy outcomes with two endometrial preparation methods. Noting that each treatment centre should select the most beneficial and cost-effective method with the least adverse effects for patients, letrozole preparations for FET could be incorporated into possible options; however, establishing this approach as first-line treatment is premature in light of current evidence, and future randomized clinical trials with larger sample sizes are required for widespread application.

TRIAL REGISTRATION

The study was also registered in the Iranian Registry of Clinical Trials on March 20th, 2020. ( IRCT20090526001952N12 at www.irct.ir , registered retrospectively).

Pregnancy Outcomes Following Letrozole Use in Frozen-thawed Embryo Transfer Cycles: A Systematic Review and Meta-analysis

While widely used for ovulation induction in assisted reproductive technology, the clinical efficacy of letrozole for endometrial preparation prior to frozen-thawed embryo transfer (FET) cycles remains yet to be elucidated. We performed a meta-analysis to compare pregnancy outcomes after letrozole use with those of other endometrial preparation protocols in patients undergoing FET. PubMed, Scopus, Embase and the Cochrane Library were searched for eligible studies. Clinical pregnancy rate (CPR), live birth rate (LBR) and birth defect rate (BDR) were analysed using odds ratio (OR) and 95% confidence interval (CI). A total of 10 studies representing 75 968 FET cycles were included. Comparable CPR and LBR were observed when comparing letrozole administration with natural cycle (OR 1.24, 95% CI: 0.69 – 2.24; OR 1.18, 95% CI: 0.60 – 2.32), artificial cycle (OR 1.46, 95% CI: 0.87 – 2.44; OR 1.39, 95% CI: 0.77 – 2.52), and artificial cycle with gonadotropin-releasing hormone agonist suppression (OR 1.11, 95% CI: 0.78 – 1.59; OR 1.18, 95% CI: 0.82 – 1.68). Pooled results of the limited studies comparing letrozole with human menopausal gonadotropin demonstrated a similar CPR between groups (OR 1.46, 95% CI: 0.29 – 7.21, two studies), but the letrozole group had a statistically lower LBR (OR 0.67, 95% CI: 0.52 – 0.86, one study). No increased BDR was observed in the letrozole group compared to natural cycles or artificial cycles (OR 0.98, 95% CI: 0.60 – 1.61; OR 1.39, 95% CI; 0.84 – 2.28). This pooled analysis supports the use of letrozole as an efficacious and safe alternative to mainstream regimens for endometrial preparation in FET cycles.