Risk of foetal harm with letrozole use in fertility treatment: a systematic review and meta-analysis

Evaluation of birth outcomes, congenital anomalies and neonatal complications of singletons born to infertile women treated with letrozole: A retrospective cohort study

At present, safety of letrozole administration as an ovulation-inducing drug still remains controversial. Investigation of the safety of letrozole use for the induction of ovulation in the Chinese population is scant. The present study aimed to fill this gap. Data concerning mothers using letrozole and birth outcomes of their singleton offspring were collected as the letrozole group (n=194), equivalent data from mothers using non-letrozole drugs and their singleton offspring were included as the non-letrozole group (control, n=154). Birth outcomes, congenital anomalies and neonatal complications were compared and analyzed between the two groups. Univariate analysis, Spearman's rank correlation analysis and the logistic regression model were utilized. For birth outcomes, the percentage of caesarean section deliveries in the letrozole group was lower than the non-letrozole group (43.8 vs. 56.4%, P=0.019). For congenital anomalies, no significant difference was found between the two groups (all P>0.05). The statistical P-value for the correlation between the maternal use of letrozole and neonatal complications was marginal (P=0.051). Results from the logistic regression analysis confirmed that maternal use of letrozole was not a significant contributor for neonatal complications, independent of statistical adjustment [crude odds ratio (OR), 1.436; 95% confidence interval (CI), 0.803-2.569; P=0.223 vs. adjusted OR, 1.406; 95% CI, 0.748-2.643; P=0.290). The results of the present study suggested that maternal use of letrozole for ovulation induction does not associate with poorer birth outcomes or increased risk of congenital anomalies and neonatal complications.

Polycystic ovary syndrome

Despite affecting ~11-13% of women globally, polycystic ovary syndrome (PCOS) is a substantially understudied condition. PCOS, possibly extending to men's health, imposes a considerable health and economic burden worldwide. Diagnosis in adults follows the International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome, requiring two out of three criteria - clinical or biochemical hyperandrogenism, ovulatory dysfunction, and/or specific ovarian morphological characteristics or elevated anti-Müllerian hormone. However, diagnosing adolescents omits ovarian morphology and anti-Müllerian hormone considerations. PCOS, marked by insulin resistance and hyperandrogenism, strongly contributes to early-onset type 2 diabetes, with increased odds for cardiovascular diseases. Reproduction-related implications include irregular menstrual cycles, anovulatory infertility, heightened risks of pregnancy complications and endometrial cancer. Beyond physiological manifestations, PCOS is associated with anxiety, depression, eating disorders, psychosexual dysfunction and negative body image, collectively contributing to diminished health-related quality of life in patients. Despite its high prevalence persisting into menopause, diagnosing PCOS often involves extended timelines and multiple health-care visits. Treatment remains ad hoc owing to limited understanding of underlying mechanisms, highlighting the need for research delineating the aetiology and pathophysiology of the syndrome. Identifying factors contributing to PCOS will pave the way for personalized medicine approaches. Additionally, exploring novel biomarkers, refining diagnostic criteria and advancing treatment modalities will be crucial in enhancing the precision and efficacy of interventions that will positively impact the lives of patients.

Impact of 2.5 mg versus 5 mg letrozole co-treatment in an antagonist protocol for IVF: a retrospective study

Objective

The present study aimed to compare the effectiveness of two different doses of letrozole (2.5 mg and 5 mg daily) in an antagonist protocol for infertile women with normal ovarian reserve.

Methods

This retrospective cohort study included infertile women who underwent in vitro fertilization treatment with letrozole co-treatment at doses of 2.5 mg and 5 mg from 2007 - 2021 at Shanghai Ninth People's Hospital (Shanghai, China). The control group comprised infertile women who received gonadotropin-releasing hormone antagonist alone. The primary outcome was the cumulative live birth rate, while secondary outcomes included follicular phase endocrine parameters, ovarian stimulation outcomes, pregnancy outcomes, and the incidences of maternal and neonatal complications. Baseline and follow-up data were compared between the groups using ANOVA for normally distributed variables, the Kruskal-Wallis test for non-normally distributed variables, and the Chi-square test for categorical variables.

Results

A total of 422 participants were enrolled in the study, with 211 women in the antagonist group, 109 women in the 2.5 mg letrozole co-treatment group, and 102 women in the 5 mg letrozole co-treatment group. Letrozole co-treatment significantly suppressed oestradiol and follicle-stimulating hormone concentrations from stimulation day 5 and onwards, while increasing luteinizing hormone levels on stimulation day 5 and trigger day. The effect was more pronounced with a 5 mg dose of letrozole compared to a 2.5 mg dose (P < 0.05). Administration of 5 mg letrozole reduced the gonadotropin dose (P < 0.05) without negatively affecting the number of oocytes retrieved and subsequent embryo parameters (P > 0.05). The analysis of cumulative live birth rates showed rates of 29.4% in the letrozole 5 mg group, 27.5% in the letrozole 2.5 mg group, and 33.6% in the control group, with no statistically significant difference (P > 0.05). There were no reported pregnancy complications in the two letrozole groups. Additionally, there were no significant differences among the three groups in terms of gestational age and birth weight for both singleton and twin births.

Conclusion

This study indicates that the administration of letrozole in an antagonist protocol, at both 2.5 mg and 5 mg dosages, results in comparable clinical outcomes.

Pregnancy and neonatal outcomes of letrozole versus natural cycle frozen embryo transfer of autologous euploid blastocyst

PURPOSE

To investigate the pregnancy and neonatal outcomes of letrozole-stimulated frozen embryo transfer (LTZ-FET) cycles compared with natural FET cycles (NC-FET).

METHODS

Our retrospective cohort included all LTZ-FET (n = 161) and NC-FET (n = 575) cycles that transferred a single euploid autologous blastocyst from 2016 to 2020 at Stanford Fertility Center. The LTZ-FET protocol entailed 5 mg of daily letrozole for 5 days starting on cycle day 2 or 3. Outcomes were compared using absolute standardized differences (ASD), in which a larger ASD signifies a larger difference. Multivariable regression models adjusted for confounders: maternal age, BMI, nulliparity, embryo grade, race, infertility diagnosis, and endometrial thickness.

RESULTS

The demographic and clinical characteristics were overall similar. A greater proportion of the letrozole cohort was multiparous, transferred high-graded embryos, and had ovulatory dysfunction. The cohorts had similar pregnancy rates (67.1% LTZ vs 62.1% NC; aOR 1.31, P = 0.21) and live birth rates (60.9% LTZ vs 58.6% NC; aOR 1.17, P = 0.46). LTZ-FET neonates on average were born 5.7 days earlier (P < 0.001) and had higher prevalence of prematurity (18.6% vs. 8.0%NC, ASD = 0.32) and low birth weight (10.4% vs. 5.0%, ASD = 0.20). Both cohorts' median gestational ages (38 weeks and 1 day for LTZ; 39 weeks and 0 day for NC) were full term.

CONCLUSION

There were similar rates of pregnancy and live birth between LTZ-FET and NC-FET cycles. However, there was a higher prevalence of prematurity and low birth weight among LTZ-FET neonates. Reassuringly, the median gestational age in both cohorts was full term, and while the difference in gestational length of almost 6 days does not appear to be clinically significant, this warrants larger studies.

Letrozole Compared With Clomiphene Citrate for Polycystic Ovarian Syndrome: A Systematic Review and Meta-analysis

OBJECTIVE

To estimate the effect of letrozole and clomiphene citrate in women with infertility and polycystic ovarian syndrome (PCOS).

METHODS OF STUDY SELECTION

MEDLINE through PubMed, Web of Science, EMBASE, Cochrane Library, and ClinicalTrials.gov were searched for relevant studies from inception to February 1, 2022. Two reviewers retrieved, filtered, and extracted data independently using the bibliographic software EndNote X9 and Excel workbook. We included randomized controlled trials (RCTs) reporting ovulation induction outcomes in women with infertility and PCOS treated with either letrozole or clomiphene citrate followed by timed intercourse or intrauterine insemination. The data were merged into a mean difference or risk ratio (RR) with 95% CI, depending on variable types.

TABULATION, INTEGRATION, AND RESULTS

Data collection and organization were conducted in accordance with the 2020 PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analyses) statement. Twenty-nine RCTs were eligible, which included 3,952 women and 7,633 ovulation induction cycles. We acquired evidence from 22 RCTs for the ovulation rate, 28 RCTs for the clinical pregnancy rate, and eight RCTs for live-birth rate. Pooled analysis indicated that letrozole treatment prevailed against clomiphene citrate in ovulation rate (RR 1.14, 95% CI 1.06-1.21, P <.001), clinical pregnancy rate (RR 1.48, 95% CI 1.34-1.63, P <.001), and live-birth rate (RR 1.49, 95% CI 1.27-1.74, P <.001).

CONCLUSIONS

Letrozole was associated with improved ovulation, pregnancy, and live-birth rates compared with clomiphene citrate. We recommend letrozole over clomiphene citrate as an ovulation induction drug in women with infertility and PCOS, although the quality of the evidence is mixed.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO, CRD42022308777.

Assessing the robustness of results from clinical trials and meta-analyses with the fragility index

The fragility index has been increasingly used to assess the robustness of the results of clinical trials since 2014. It aims at finding the smallest number of event changes that could alter originally statistically significant results. Despite its popularity, some researchers have expressed several concerns about the validity and usefulness of the fragility index. It offers a comprehensive review of the fragility index's rationale, calculation, software, and interpretation, with emphasis on application to studies in obstetrics and gynecology. This article presents the fragility index in the settings of individual clinical trials, standard pairwise meta-analyses, and network meta-analyses. Moreover, this article provides worked examples to demonstrate how the fragility index can be appropriately calculated and interpreted. In addition, the limitations of the traditional fragility index and some solutions proposed in the literature to address these limitations were reviewed. In summary, the fragility index is recommended to be used as a supplemental measure in the reporting of clinical trials and a tool to communicate the robustness of trial results to clinicians. Other considerations that can aid in the fragility index's interpretation include the loss to follow-up and the likelihood of data modifications that achieve the loss of statistical significance.

Current pharmacotherapy and future directions for neuroendocrine causes of female infertility

INTRODUCTION

Infertility is recognized as a major global health issue, often associated with significant psychological distress for affected couples. Causes of female infertility include endocrine conditions leading to oligo/anovulation, in addition to structural causes such as tubal, uterine, or peritoneal disorders. Pharmacological treatments, targeting pathways in the hypothalamic-pituitary-ovarian axis, can improve rates of ovulation, conception, pregnancy, and birth. Some existing therapeutic options are hindered by limited efficacy or by a non-physiological mechanism, which can risk excessive stimulation and treatment-related adverse effects. Therefore, there is a continued need for novel therapies to improve care for patients suffering with infertility.

AREAS COVERED

In this review, the authors focus on endocrine causes of oligo/anovulation in women and on advances in assisted reproductive technology. Current pharmacological treatments and putative future therapeutic avenues in development to aid fertility in women are outlined.

EXPERT OPINION

A deeper understanding of the reproductive neuroendocrine network governing hypothalamic gonadotropin-releasing hormone release can offer novel therapeutic targets for the treatment of female subfertility, leading to improved clinical outcomes, less invasive routes of administration, and decreased treatment-related side-effects. The ultimate aim of development in female subfertility is to offer therapeutic interventions that are effective, reproducible, associated with minimal risks, and have an acceptable route of administration.

Ovarian Drilling: Back to the Future

Polycystic ovary syndrome (PCOS) is the leading cause of anovulatory infertility. The complex metabolic dysregulation at the base of this syndrome often renders infertility management challenging. Many pharmacological strategies have been applied for the induction of ovulation with a non-negligible rate of severe complications such as ovarian hyperstimulation syndrome and multiple pregnancies. Ovarian drilling (OD) is currently being adopted as a second-line treatment, to be performed in case of medical therapy. Laparoscopic ovarian drilling (LOD), the contemporary version of ovarian wedge resection, is considered effective for gonadotropins in terms of live birth rates, but without the risks of iatrogenic complications in gonadotropin therapy. Its endocrinal effects are longer lasting and, after the accomplishment of this procedure, ovarian responsiveness to successive ovulation induction agents is enhanced. Traditional LOD, however, is burdened by the potential risks of iatrogenic adhesions and decreased ovarian reserve and, therefore, should only be considered in selected cases. To overcome these limits, novel tailored and mini-invasive approaches, which are still waiting for wide acceptance, have been introduced, although their role is still not well-clarified and none of them have provided enough evidence in terms of efficacy and safety.

Perinatal outcomes and congenital anomalies associated with letrozole and natural cycles in single fresh cleaved embryo transfers: A single-center, 10-year cohort study

Objective

To investigate and compare the safety of letrozole and natural cycles in fresh early embryo transfers.

Design

A retrospective cohort study.

Setting

A large fertility treatment center.

Patient(s)

Women who underwent natural and letrozole cycles during fresh early embryo transfer at Kato Ladies Clinic between January 2008 and December 2017.

Intervention(s)

None.

Main Outcome measure(s)

Perinatal complications and congenital anomalies.

Result(s)

No significant differences were observed in pregnancy complications, gestational age, birth weight, small for gestational age, large for gestational age, and congenital anomalies between the the women who underwent natural and letrozole cycles.

Conclusion(s)

The perinatal outcomes and congenital anomaly rates associated with letrozole and natural cycles in fresh early embryo transfers were comparable. Therefore, our data support the safe use of letrozole in fresh early embryo transfers in assisted reproductive technology.

Letrozole Supplementation and the Increased Risk of Elevated Progesterone Levels on Trigger Day

Although using letrozole (LE) during in vitro fertilisation and intracytoplasmic sperm injection (IVF/ICSI) has many advantages, it remains unclear whether LE induces an increase in progestogen during the late follicular phase. The objective of this study was to investigate whether progesterone levels increased under antagonist protocols supplemented with LE on the trigger day using a retrospective cohort study. The study included 1,133 women who underwent IVF/ICSI cycles from January 2018 to June 2020. After propensity score matching (PSM) for baseline characteristics, 266 patients with gonadotropin-releasing hormone-antagonist (GnRH-ant) were matched to 266 patients with letrozole + GnRH-ant (LE GnRH-ant) (PSM 1 cohort), and 283 patients with gonadotropin-releasing hormone-agonist (GnRH-a) were matched to 283 patients with LE GnRH-ant (PSM 2 cohort). In the PSM 1 cohort, patients in the LE GnRH-a group presented higher progesterone levels (1.22 ± 0.95 ng/mL vs 0.86 ± 0.60 ng/mL, P < 0.001), with a higher proportion of patients with progesterone level > 1.5 ng/mL (24.81% vs 7.52%, P < 0.001). In PSM 2 cohort, patients in the LE GnRH-a group presented higher progesterone levels on trigger day (1.23 ± 0.91 ng/mL vs 0.98 ± 0.61 ng/mL, P < 0.001), with a higher proportion of patients with progesterone level > 1.5 ng/mL (25.45% vs 12.70%, P < 0.001). In the PSM 1 cohort, progesterone levels on the trigger day increased by 0.05 ng/mL, with an increase in every retrieved oocyte in the LE GnRH-ant group (β 0.05 ng/mL [95% CI 0.04, 0.06], P < 0.001), whereas an increase of 0.02 ng/mL was observed in the GnRH-ant group (β 0.02 ng/mL [95% CI 0.01, 0.03], P < 0.001), with P for interaction being 0.0018. In the PSM 2 cohort, progesterone levels on the trigger day increased by 0.05 ng/mL with an increase in every retrieved oocyte in the LE GnRH-ant group (β 0.05 ng/mL [95% CI 0.04, 0.06], P < 0.001), whereas an increase of 0.02 ng/mL was observed in the GnRH-a group (β 0.02 ng/mL [95% CI 0.01, 0.03], P < 0.001), with P for interaction being 0.0002. LE supplementation on the antagonist protocols may increase progesterone levels in the late follicular stage.

OUP accepted manuscript

BACKGROUND

Intrauterine insemination with ovarian stimulation (IUI-OS) is a first-line treatment for unexplained infertility. Gonadotrophins, letrozole and clomiphene citrate (CC) are commonly used agents during IUI-OS and have been compared in multiple aggregate data meta-analyses, with substantial heterogeneity and no analysis on time-to-event outcomes. Individual participant data meta-analysis (IPD-MA) is considered the gold standard for evidence synthesis as it can offset inadequate reporting of individual studies by obtaining the IPD, and allows analyses on treatment–covariate interactions to identify couples who benefit most from a particular treatment.

OBJECTIVE AND RATIONALE

We performed this IPD-MA to compare the effectiveness and safety of ovarian stimulation with gonadotrophins, letrozole and CC and to explore treatment–covariate interactions for important baseline characteristics in couples undergoing IUI.

SEARCH METHODS

We searched electronic databases including MEDLINE, EMBASE, CENTRAL, CINAHL, and PsycINFO from their inception to 28 June 2021. We included randomized controlled trials (RCTs) comparing IUI-OS with gonadotrophins, letrozole and CC among couples with unexplained infertility. We contacted the authors of eligible RCTs to share the IPD and established the IUI IPD-MA Collaboration. The primary effectiveness outcome was live birth and the primary safety outcome was multiple pregnancy. Secondary outcomes were other reproductive outcomes, including time to conception leading to live birth. We performed a one-stage random effects IPD-MA.

OUTCOMES

Seven of 22 (31.8%) eligible RCTs provided IPD of 2495 couples (62.4% of the 3997 couples participating in 22 RCTs), of which 2411 had unexplained infertility and were included in this IPD-MA. Six RCTs (n = 1511) compared gonadotrophins with CC, and one (n = 900) compared gonadotrophins, letrozole and CC. Moderate-certainty evidence showed that gonadotrophins increased the live birth rate compared to CC (6 RCTs, 2058 women, RR 1.30, 95% CI 1.12–1.51, I² = 26%). Low-certainty evidence showed that gonadotrophins may also increase the multiple pregnancy rate compared to CC (6 RCTs, 2058 women, RR 2.17, 95% CI 1.33–3.54, I² = 69%). Heterogeneity on multiple pregnancy could be explained by differences in gonadotrophin starting dose and choice of cancellation criteria. Post-hoc sensitivity analysis on RCTs with a low starting dose of gonadotrophins (≤75 IU) confirmed increased live birth rates compared to CC (5 RCTs, 1457 women, RR 1.26, 95% CI 1.05–1.51), but analysis on only RCTs with stricter cancellation criteria showed inconclusive evidence on live birth (4 RCTs, 1238 women, RR 1.15, 95% CI 0.94–1.41). For multiple pregnancy, both sensitivity analyses showed inconclusive findings between gonadotrophins and CC (RR 0.94, 95% CI 0.45–1.96; RR 0.81, 95% CI 0.32–2.03, respectively). Moderate certainty evidence showed that gonadotrophins reduced the time to conception leading to a live birth when compared to CC (6 RCTs, 2058 women, HR 1.37, 95% CI 1.15–1.63, I² = 22%). No strong evidence on the treatment–covariate (female age, BMI or primary versus secondary infertility) interactions was found.

WIDER IMPLICATIONS

In couples with unexplained infertility undergoing IUI-OS, gonadotrophins increased the chance of a live birth and reduced the time to conception compared to CC, at the cost of a higher multiple pregnancy rate, when not differentiating strategies on cancellation criteria or the starting dose. The treatment effects did not seem to differ in women of different age, BMI or primary versus secondary infertility. In a modern practice where a lower starting dose and stricter cancellation criteria are in place, effectiveness and safety of different agents seem both acceptable, and therefore intervention availability, cost and patients’ preferences should factor in the clinical decision-making. As the evidence for comparisons to letrozole is based on one RCT providing IPD, further RCTs comparing letrozole and other interventions for unexplained infertility are needed.

Co-Administration of Clomiphene Citrate and Letrozole in Mild Ovarian Stimulation Versus Conventional Controlled Ovarian Stimulation Among POSEIDON Group 4 Patients

This retrospective study assessed the effect of the co-administration of clomiphene citrate (CC) and letrozole in mild ovarian stimulation, compared to conventional regimens, among Patient-Oriented Strategies Encompassing Individualized Oocyte Number (POSEIDON) Group 4 patients. There were 114 POSEIDON Group 4 patients undergoing in vitro fertilization treatments with 216 stimulation cycles recruited from a Taiwan's reproductive center during 2016-2020. Main outcomes were the numbers, quality of retrieved oocytes and embryo development. Pregnancy outcomes were assessed after embryo transfers. Per stimulation cycle, patients receiving mild stimulation with a combination of CC and letrozole (study group) versus those with COS (control group) had lower numbers of pre-ovulatory follicles (2.00 ± 1.23 vs. 2.37 ± 1.23, p=0.0066) and oocytes retrieved (1.83 ± 1.17 vs. 2.37 ± 1.23, p=0.0017), and lower follicular output rate (58.6% vs. 68.38%, p=0.0093) and mature oocyte output rate (44.29% vs. 52.88%, p=0.0386) but a higher top-quality metaphase II oocyte ratio (66.7% vs. 54.59%, p=0.0444) and a similar fertilization rate (91.67% vs. 89.04%, p=0.4660). With adjustment for significant between-group baseline differences using multivariable logistic generalized estimating equation model analyses, there was no statistical difference in oocytes retrieved and embryo development between the study and control groups, and insignificant increases in successful pregnancies in the study group were found compared to the control group (i.e., odds ratios [95% CIs]: 1.13 [0.55, 232] and 1.50 [0.65, 3.49] for ongoing pregnancy and live birth, respectively). For POSEIDON Group 4 patients, cotreatment of CC and letrozole in mild stimulation may increase the high-quality oocyte ratio and yield comparable fertilization rate and pregnancy outcomes.