Clinical use of recombinant human luteinizing hormone beyond hypogonadotropic hypogonadism: a multicenter descriptive analysis from five Italian fertility centers.

The present multicenter retrospective cohort study was conducted across the Infertility Units of 5 different public hospitals in Italy: IRCCS Humanitas Research Hospital (Milan), Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico (Milan), IRCCS San Raffaele Scientific Institute, Hospital Papa Giovanni XXIII (Bergamo), Sant’Anna Hospital (Turin). All women who were referred to the 5 IVF Units between January 2018 and December 2023 to undergo either conventional IVF or intracytoplasmic sperm injection (ICSI) were reviewed. Only homologous in vitro fertilization cycles were included. Patients who were prescribed a fixed-ratio (2:1) combination of rFSH and rLH, were deemed eligible for study entry. In the case where the patient underwent multiple stimulation cycles with rFSH/rLH, only the first stimulation cycle was considered and analysed. Patients whose partners had severe forms of male infertility (i.e., men with sperm concentration < 1000000/ml or who underwent surgical sperm retrieval) were excluded. Data were extracted using the Fertility EMR (Electronic Medical Record) software used in the different IVF Units. The study protocol was approved by the institutional review board at the IRCCS Fondazione Ca’ Granda Ospedale Maggiore Policlinico (determination nr. 6495_15/10/2025). An informed consent was not requested due to the retrospective nature of the study. However, all women referring to the participating Units provide an informed consent for their data to be used for research purposes and those denying this consent were excluded. All women scheduled for IVF underwent both biochemical (i.e., assessment of serum anti-Müllerian hormone (AMH), FSH, and estradiol concentration) and ultrasonographic (i.e., assessment of the antral follicle count (AFC)) quantitative ovarian reserve evaluation [ 12 ]. Adopted COS protocols included long and short GnRH agonist protocols and fixed or variable GnRH antagonist protocols. The decision to administer either rFSH/rLH or rFSH alone was based on the treating physician’s clinical judgment within routine practice at each participating center. Gonadotropin dosage was individualized according to patients’ characteristics, always keeping the fixed ratio. The choice of the gonadotropin starting dose was based on predictive variables like body mass index (BMI), female age and ovarian reserve tests, including AMH, AFC, and FSH. In all COS cycles, ultrasound monitoring was performed to monitor the follicular growth (in number and size). The first transvaginal ultrasound scan was performed between day 1 and day 3 of the menstrual cycle or after achieving ovarian downregulation. The second monitoring ultrasound was conducted after 5 or 6 days of gonadotropin administration. Subsequent ultrasound evaluations were carried out every 1, 2, or 3 days based on the individual response to COS, up to the day of ovulation triggering (i.e., when the leading follicles reached a minimum diameter of 18 mm). Ovulation trigger was performed using hCG in patients undergoing GnRH agonist protocols. In women treated with GnRH antagonist protocols, the choice of trigger was based on the extent of the ovarian response. Specifically, in patients with an expected retrieval of ≥ 15–18 oocytes (depending on the IVF Unit), either a GnRH agonist trigger alone or a dual trigger was administered, in accordance with the protocol in place at each individual IVF Unit. Oocyte retrieval was subsequently performed 36 h later, via transvaginal ultrasound-guided aspiration. Fresh embryo transfer (ET) was conducted either at the cleavage stage (48–72 h post-oocyte retrieval) or, in select cases, at the blastocyst stage (5 days post-oocyte retrieval). Supernumerary embryos were cryopreserved at the cleavage or at the blastocyst stage according to the protocol of the different IVF Units. Frozen-thawed ET were carried out either in a natural cycle or following hormone replacement therapy. The following three endometrial preparation protocols were adopted in frozen-thawed ET cycles: true natural cycle, modified natural cycle and artificial cycle. The data were obtained from the patients’ clinical and biological records. They included demographic and clinical information, as well as details about the IVF procedures and pregnancy outcomes. In accordance with the Italian regulations, a routine follow-up of all pregnancies was conducted around the expected date of delivery. Information on the course of pregnancy was gathered using obstetric charts for women who delivered at the participating hospitals. For those who delivered elsewhere, the information was obtained through phone calls. Any inconsistencies or missing data were addressed through additional phone contacts. The primary outcome was the cumulative live birth rate (cLBR) defined as the number of deliveries with at least one live birth resulting from one initiated or aspirated IVF/ICSI cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one delivery (the delivery of a singleton, twin, or other multiples is registered as one delivery) with a live birth occurs or until all embryos are used, whichever occurs first [ 13 ]. The secondary outcome was the cumulative clinical pregnancy rate (cCPR) per oocyte retrieval defined as the number of clinical pregnancies resulting from one initiated or aspirated IVF/ICSI cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one clinical pregnancy occurs or until all embryos are used, whichever occurs first. Clinical pregnancy was defined as a pregnancy diagnosed by ultrasonographic visualization of one or more intrauterine gestational sacs [ 13 ]. Subgroup analyses were performed according to female age (≤ 34 years, 35–39 years, 40–42 years, ≥ 43 years), and LH level (< 6 mIU/ml, ≥ 6 mIU/ml). Additional multivariable logistic regression analyses including baseline LH as a covariate were performed. Both the cLBR and the cCPR were expressed as percentage and 95% confidence interval (CI). Continuous variables were reported as median [IQR], while categorical variables were reported as percentages. When comparisons were performed, Chi square and Mann–Whitney tests were run to investigate any statistical difference between groups. In order to identify independent predictors of cCPR and cLBR per oocyte retrieval, multivariable logistic regression analyses were performed, including the following covariates: female age, BMI, AMH, total FSH dose and Center. The software Statistical Package for Social Sciences (SPSS, Chicago, IL, USA), version 27.0, was used to analyse the data.

Overall, 9,703 IVF/ICSI cycles were included in the study. Baseline characteristics are shown in Table  1 . The median female age was 39 [36–41] years and the median male age was 40 [37–44] years. The median female BMI was 21.6 [19.8–24.1]. The majority (95%) of included IVF/ICSI cycles were first attempts. The median duration of infertility was 3 [2–5] years. With respect to reproductive history, 10% percent of the women included in the study had previously given birth to at least one child, while 31% had experienced at least one pregnancy. Table 1 Baseline characteristics of the studied group ( n  = 9,703) Characteristics Study group n  = 9,703 Female age (years) 39 [36–41] Male age (years) 40 [37–44] BMI (Kg/m 2 ) 21.6 [19.8–24.1] Previous oocyte retrieval 489 (5%) Previous gynecological surgery 1,876 (19%) Duration of infertility (years) 3 [2–5] Previous delivery 958 (10%) Previous pregnancy 2,976 (31%) Cause of infertility  Endometriosis 507 (5%)  Tubal factor 1,497 (15%)  Reduced ovarian reserve 2,351 (24%)  Ovulation disorders 148 (2%)  Unexplained 727 (7%)  Recurrent pregnancy loss 54 (1%)  Genetic disease 65 (1%)  Male factor 1,594 (16%)  Mixed 2,760 (28%) AMH (ng/ml) 1.00 [0.55–1.80] AFC 6 [4–9] FSH (IU/L) 8,4 [6,6–10,9] LH (IU/L) 5,2 [3,9 − 7,0] Estradiol (pg/mL) 49 [34–68] Data are reported as median [interquartile range] or number (percentage) BMI Body Mass Index, AMH Anti-Mullerian Hormone, AFC Antral Follicle Count Baseline characteristics of the studied group ( n  = 9,703) Data are reported as median [interquartile range] or number (percentage) BMI Body Mass Index, AMH Anti-Mullerian Hormone, AFC Antral Follicle Count The main IVF indications were mixed infertility (28%), followed by reduced ovarian reserve (24%) and tubal factor (15%). Ovarian reserve markers showed a median AMH of 1.00 [0.55–1.80] ng/ml and a median AFC of 6 [4–9]. Data regarding the IVF/ICSI cycles are summarized in Table  2 . The median COS length was 12 days and the median total dose of gonadotropin was 3,600 UI. The most commonly used stimulation protocol was the GnRH antagonist protocol (58%), followed by the GnRH agonist “flare-up” protocol (21%) and the GnRH agonist long protocol (20%). In 12% of cases the cycle was cancelled, mainly due to insufficient ovarian response (82%). Induction of ovulation was triggered mostly with hCG (83%). At the time of trigger the median estrogen level was 1,493 [851–2,327] µg/l, and the median progesterone level was 0.73 [0.48–1.08] µg/l. Overall, 8,548 oocyte retrievals were carried out. The median number of retrieved oocytes per aspiration was 6 [4–9]. In 93% of cycle ICSI was performed, with an average of 4 [3–7] oocytes inseminated per cycle. Lastly, 6,125 women underwent fresh ET, mostly of cleavage stage embryos (86.7%). In 2,423 cycles fresh ET was not performed, mostly due to OHSS (22%), failed oocytes fertilization (18%) and failed cleavage (12%). Table 2 Characteristics of the IVF cycles in the studied group ( n  = 9,703) Characteristics Study group n  = 9,703 Duration of stimulation (days) 12 [11–13] Total dose of FSH administered (UI) 3.600 [2.775–4.350] Regimen of ovarian hyper-stimulation  GnRH Antagonist 5,600 (58%)  Flare-up protocol 2,090 (21%)  Long protocol 1,905 (20%) Cancelled cycles 1,155 (12%)  Insufficient ovarian response 947 (82%)  Medical complications 9 (1%)  Other 199 (17%) Induction of ovulation  hCG 8,095 (83%)  GnRH 485 (5%)  hCG+GnRH 232 (2%) Estradiol at the time of trigger administration (pg/mL) 1.493 [851–2.327] Progesterone at the time of trigger administration (pg/mL) 0,73 [0,48 − 1,08] Endometrial thickness at the time of trigger administration (mm) 9,5 [8–11] Number of oocyte retrievals 8,548 Total number of oocytes retrieved 6 [4–9] Total number of suitable oocytes 4 [3–7] IVF technique used  IVF 552 (7%)  ICSI 7,694 (93%) Number of fresh embryo transfer 6,125  Cleavage stage 5,310 (86,7%)  Blastocyst stage 815 (13,3%) Number of not performed fresh embryo transfer 2,423  No retrieved oocytes 64 (3%)  No suitable oocytes 190 (8%)  No fertilized oocytes 440 (18%)  No cleavage embryos 295 (12%)  Ovarian hyper-stimulation syndrome 526 (22%)  Pre-implantation genetic testing 263 (11%)  Elevated progesterone 147 (6%)  Other 498 (20%) Data are reported as median [interquartile range] or number (percentage) IVF in vitro fertilization, ICSI intracytoplasmatic sperm injection Characteristics of the IVF cycles in the studied group ( n  = 9,703) Estradiol at the time of trigger administration (pg/mL) Progesterone at the time of trigger administration (pg/mL) Endometrial thickness at the time of trigger administration (mm) Data are reported as median [interquartile range] or number (percentage) IVF in vitro fertilization, ICSI intracytoplasmatic sperm injection Obstetric outcome is summarized in Table  3 . Overall, 3,212 patients got pregnant, and 2,313 patients delivered a healthy baby, thus leading to a LBR of 24% [95%CI: 23–25] per cycle and 27% [95%CI: 26–29 per oocyte retrieval and a CPR of 33% [95%CI: 32–34] per cycle and 38% [95%CI: 37–39] per oocyte retrieval. Table 3 Obstetric outcomes the studied group ( n  = 9,703) Characteristics Study group n  = 9,703 Total number of clinical pregnancy 3,212 Cumulative CPR  per cycle 33% [32–34]  per oocyte retrieval 38% [37–39] Total number of live births 2,313 Cumulative LBR  per cycle 24% [23–25]  per oocyte retrieval 27% [26–28] Data are reported as percentage [95% confidence interval (CI)] CPR clinical pregnancy rate, defined as the number of clinical pregnancies resulting from one initiated or aspirated IVF/ICSI cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one clinical pregnancy occurs or until all embryos are used, whichever occurs first. Clinical pregnancy was defined as a pregnancy diagnosed by ultrasonographic visualization of one or more intrauterine gestational sacs. LBR live birth rate, defined as the number of deliveries with at least one live birth resulting from one initiated or aspirated IVF/ICSI cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one delivery (the delivery of a singleton, twin, or other multiples is registered as one delivery) with a live birth occurs or until all embryos are used, whichever occurs first Obstetric outcomes the studied group ( n  = 9,703) Data are reported as percentage [95% confidence interval (CI)] CPR clinical pregnancy rate, defined as the number of clinical pregnancies resulting from one initiated or aspirated IVF/ICSI cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one clinical pregnancy occurs or until all embryos are used, whichever occurs first. Clinical pregnancy was defined as a pregnancy diagnosed by ultrasonographic visualization of one or more intrauterine gestational sacs. LBR live birth rate, defined as the number of deliveries with at least one live birth resulting from one initiated or aspirated IVF/ICSI cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one delivery (the delivery of a singleton, twin, or other multiples is registered as one delivery) with a live birth occurs or until all embryos are used, whichever occurs first Univariate analyses were performed. A significant correlation emerged between maternal age and surrogate markers of ovarian reserve (i.e., serum AMH, AFC and serum FSH) and LBR. Flare up protocol showed a significant lower LBR compared to GnRH antagonist protocol. No significant correlation emerged when follicle‑to‑oocyte index [FOI: (number of retrieved oocytes/antral follicle count) × 100] was considered (Table  4 ). Multivariable logistic regression analyses identified female age and AMH as variables significantly associated with LBR and CPR. No other associations emerged (Table  5 ). Table 4 Univariate analyses Characteristics OR [95% CI] p -value Female age 0.87 [0.86 – 0.88] <0.001 AMH (ng/mL) 1,12 [1.05 – 1.13] <0.001 AFC 1.04 [1.02 - 1.05] 0.001 FSH (UI/L) 1.01 [1.00 – 1.04] 0.022 LH (UI/L) 1.00 [0.98 – 1.01] 0.65 Protocol of ovarian hyper-stimulation (compared to GnRH antagonist) Flare-up 1.02 [0.89 - 1.16] 1.00 Long protocol 0.64 [0.59 - 0.78] <0.001 FOI 1.03 [0.99 - 1.06] 0.14 OR Odds ratio, CI confidence interval,  AMH Anti-Mullerian Hormone, AFC Antral Follicle Count,  FOI Follicle-to-oocyte index (number of retrieved oocytes/antral follicle count) Univariate analyses OR Odds ratio, CI confidence interval,  AMH Anti-Mullerian Hormone, AFC Antral Follicle Count,  FOI Follicle-to-oocyte index (number of retrieved oocytes/antral follicle count) Table 5 Multivariate analyses Characteristics OR [95% CI] p -value cCPR  Female age 0.90 [0.88–0.91] < 0.001  BMI 1.00 [0.98–1.02] 0.70  AMH (ng/mL) 1.06 [1.03–1.09] < 0.001  Total Dose (UI) 1.00 [1.00–1.00] 0.35  Center* 0.11   Center 2 1.22 [1.00–1.50] 0.05   Center 3 1.00 [0.83–1.23] 0.93   Center 4 0.89 [0.64–1.25] 0.51   Center 5 0.62 [0.35–1.12] 0.11 cLBR  Female age 0.88 [0.86–0.89] < 0.001  BMI 0.98 [0.97–1.00] 0.09  AMH (ng/mL) 1.06 [1.03–1.10] < 0.001  Total Dose (UI) 1.00 [1.00–1.00] 0.48  Center* 0.15   Center 2 1.00 [0.79–1.27] 0.98   Center 3 0.79 [0.62–0.99] 0.04   Center 4 0.88 [0.60–1.30] 0.53   Center 5 0.57 [0.29–1.11] 0.10 OR Odds ratio, CI confidence interval, AMH Anti-Mullerian Hormone *Center 1 was used as the reference category Multivariate analyses OR Odds ratio, CI confidence interval, AMH Anti-Mullerian Hormone *Center 1 was used as the reference category Dividing the patients into four age groups (≤ 34 years, 35–39 years, 40–42 years, ≥ 43 years), a progressive reduction in LBR and CPR with increasing female age was observed (Table  6 ). No differences emerged in LBR and CPR when patients were divided according to baseline LH levels (< 6 mIU/ml vs. ≥ 6 mIU/ml) (Tables  7 ). The additional multivariable logistic regression analyses performed including baseline LH, showed that baseline LH was not independently associated with cLBR and cCPR (data not shown). Table 6 Subgroup analysis according to female age ≤ 34 years 35–39 years 40–42 years ≥ 43 years p -value Total nr of IVF cycles 1,353 5,284 2,737 329 Cumulative CPR 44 [41–47] 39 [38–40] 19 [18–21] 11 [8–15] < 0.001 Cumulative LBR 34 [32–37] 28 [27–29] 13 [12–14] 5 [3–8] <0.001 Total nr of oocytes retrievals 1,239 4,648 2,386 275 Cumulative CPR 48 [45–51] 44 [43–46] 22 [20–24] 13 [9–18] < 0.001 Cumulative LBR 37 [34–40] 32 [31–33] 15 [14–16] 6 [4–10] < 0.001 Data success rates are reported as % and 95% confidence interval (CI) IVF in vitro fertilization, Nr : number, CPR clinical pregnancy rate, LBR live birth rate Subgroup analysis according to female age Data success rates are reported as % and 95% confidence interval (CI) IVF in vitro fertilization, Nr : number, CPR clinical pregnancy rate, LBR live birth rate Table 7 Subgroup analysis according to LH serum levels < 6 UI/L ≥ 6UI/L p -value Female age 39 [36–41] 39 [36–41] Total number of IVF cycle 5,319 3,056 Total number of cancelled cycles 664 (12%) 373 (12%)  0.71 Total number of oocytes retrievals 4,655 2,683 CPR per cycle 1,042 (20%) 603 (20%) > 0.05 CPR per oocyte retrieval 1,042 (22%) 603 (22%) > 0.05 Data are reported as percentage CPR clinical pregnancy rate, IVF in vitro fertilization Subgroup analysis according to LH serum levels Data are reported as percentage CPR clinical pregnancy rate, IVF in vitro fertilization

Controlled ovarian stimulation (COS) represents a key step in the in-vitro fertilization (IVF) process. It has been demonstrated that the choice of the stimulation protocol as well as the type and dose of gonadotropin to be used can significantly influence the success rates and safety profile of the treatment. As for gonadotropins, the administration of exogenous follicle stimulating hormone (FSH) has been the basis of most ovarian stimulation protocols for many years. More recently, the administration of exogenous luteinizing hormone (LH), in combination with FSH, has also gained ground. LH exerts two crucial activities during folliculogenesis. First of all, it induces androgen production in theca cells. Second, it cooperates with FSH in stimulating the local production of inhibin B and growth factors. Notably, for an optimal follicular maturation, LH concentration must fall within a specific therapeutic window, ranging from 1.2 IU/L to 5 IU/L [ 1 ]. Based on the notions learned from physiology, the administration of LH combined with FSH during COS in LH deficient women was hypothesized to have beneficial effects on growing follicles and, as a result, on the fertility treatments success rate [ 2 ]. The first source of exogenous LH was obtained from the urine of post-menopausal women: it is known as human menopausal gonadotropin, and it contains a mixture of FSH, LH and human chorionic gonadotropin (hCG) in different amounts [ 3 , 4 ]. Later, recombinant LH (rLH) was introduced. It is an analogue of endogenous LH characterized by high purity and precise dosing, with a terminal half-life of 24 h and modest accumulation [ 5 ]. rLH was originally commercialized to supplement rFSH stimulation in a specific population of women with severe FSH and LH deficiency, namely patients with hypogonadotropic hypogonadism, defined as LH serum levels < 1.2 UI/l [ 2 , 6 ]. Subsequently, products with a fixed-dose, fixed-ratio (2:1) combination of rFSH hormone plus rLH were introduced, after having identified this combination as the optimal FSH: LH ratio to promote follicular development [ 7 ]. Although hypogonadotropic hypogonadism remains the primary indication for the use of rLH, its application has been proposed in other clinical scenarios: (i) LH deficiency induced by gonadotropin releasing hormone (GnRH) analogue protocols; (ii) reduced LH activity in women of advanced maternal age (AMA); (iii) hypo-response to ovarian stimulation due to diminished LH activity; and (iv) reduced LH activity in the context of ovarian stimulation related to genetic variants [ 8 , 9 ]. Promising evidence is emerging regarding the efficacy of rLH in these conditions, which mimic hypogonadotropic hypogonadism; however, current data remain insufficient to draw definitive conclusions. To date, real-world data analyses from large cohorts are scarce, limiting the ability to evaluate not only intermediate outcomes (e.g., number of oocytes retrieved, implantation rate, and clinical pregnancy rate [CPR]) but also critical endpoints such as live birth rate (LBR) and cumulative live birth rate (cLBR), the latter of which is now widely regarded as the most comprehensive indicator of IVF success [ 11 ]. Against this background, the aim of the present multicentre observational study, conducted on a large real-world cohort, was to characterize the IVF population in which a fixed combination of rFSH/rLH is prescribed, and to analyse both point-specific and cumulative outcomes associated with its use. A secondary objective was to identify subpopulations in which this combination demonstrated the greatest efficacy.

In the present study, we provided a descriptive analysis of the clinical use of the fixed-ratio (2:1) combination of rFSH and rLH for controlled ovarian stimulation (COS) in IVF/ICSI cycles. Our findings indicate that this formulation is predominantly prescribed to women of advanced reproductive age with clinical and ultrasonographic features consistent with severely diminished ovarian reserve. This prescribing pattern is consistent with current evidence. rLH supplementation has been shown to improve live birth rate (LBR) and cumulative LBR (cLBR) not only in patients with hypogonadotropic hypogonadism but also in selected subgroups of women fulfilling the Bologna criteria for poor ovarian response. In particular, patients with higher scores in the Poor Responder Outcome Prediction (PROsPeR) model appear to derive the greatest benefit from rLH supplementation. Moreover, LH activity has been reported to provide clinical benefit in women of advanced age undergoing COS as well as in so-called hypo-responders [ 9 ]. Importantly, based on currently available literature, there is no evidence of an increased risk of OHSS with the use of rLH [ 10 ]. The overall OHSS rate in this study population was 5.4%. Although rLH supplementation was used in a proportion of stimulation cycle, the retrospective design of the study and the presence of multiple confounding factors influencing OHSS risk, prevent any casual inference regarding a potential association between rLH use and the observed OHSS rate. In our cohort, both cumulative clinical pregnancy rate (cCPR) and cumulative live birth rate (cLBR) were significantly associated with female age, AFC, AMH levels, and baseline FSH concentrations, whereas baseline serum LH levels were not associated with clinical outcomes. Given the observational design and the absence of a control group, treatment efficacy cannot be directly assessed. Therefore, outcomes were interpreted in comparison with real-world reference data. The Italian National Assisted Reproductive Technology (ART) Registry, published annually by the Istituto Superiore di Sanità, represents an appropriate benchmark. According to registry data from 2019 to 2022, cCPRs per initiated cycle in women aged ≥ 35 years were 23.1–27.6% in women aged 35–39 years, 8.9–12.4% in those aged 40–42 years, and 3.2–4.8% in women aged ≥ 43 years ( https://www.iss.it/rpma-dati-registro/-/asset_publisher/o8HUjPKK6FoG/content/elenco-report-attivita-del-registro-nazionale-italiano-della-procreazione-medicalmente-assistita ). In our cohort, age-stratified cLBRs were slightly higher than national averages, despite the markedly diminished ovarian reserve and relatively low number of retrieved oocytes observed in our population. These findings are broadly consistent with previously published studies. Law et al. (2019), analysing data from the Australian and New Zealand Assisted Reproduction Database, reported a cLBR per aspiration of 32% in women aged 35–39 years retrieving eight oocytes and 8% in women aged 40–44 years retrieving five oocytes [ 14 ]. More recently, Polanski et al. (2024) evaluated women with poor ovarian response undergoing COS with either rFSH or highly purified human menopausal gonadotropin (HP-hMG). In patients aged 40–42 and 43–45 years retrieving four oocytes, cLBRs per aspiration were 11.6% and 5.6%, respectively [ 15 ]. In our cohort, the corresponding cLBRs were 15% and 6%. When the entire study populations were considered regardless of oocyte yield, average cLBRs were 7.3% and 1.6%, respectively [ 15 ]. Although these comparisons should be interpreted cautiously, they may suggest a potential favourable impact of the fixed rFSH/rLH combination on reproductive outcomes in older women. The main limitation of this study is the absence of a control group, which prevents direct comparisons with other stimulation regimens. However, this reflects the descriptive design of the study, whose aim was to provide a real-world overview of the use of the fixed-ratio rFSH/rLH combination in routine clinical practice and to address the current lack of large real-world datasets on this treatment. Nevertheless, the present analysis provides useful insights and may serve as a basis for future comparative studies.

Several relevant insights emerge from our findings. First, the fixed-ratio rFSH/rLH combination appears to be primarily used in women of advanced maternal age with poor or very poor prognosis. Second, baseline serum LH concentrations do not seem to significantly influence clinical outcomes in patients undergoing COS with this regimen. This observation challenges the assumption that LH supplementation should be guided by circulating LH levels and supports a more phenotype-based approach to treatment selection. Evidence supporting the clinical benefit of rFSH/rLH remains limited and sometimes inconclusive. This is reflected in the most recent ESHRE guidelines on ovarian stimulation for IVF/ICSI, which include only one recommendation regarding this combination: “The use of rFSH + rLH for ovarian stimulation is probably not recommended over hMG in GnRH agonist protocols with regards to safety” [ 16 ]. When interpreted alongside national registry data and previously published studies, our findings may raise the possibility that the fixed rFSH/rLH combination could be associated with slightly higher cumulative ART success rates compared with rFSH alone or HP-hMG, particularly among women of advanced maternal age. Although the differences appear modest, they may still be clinically meaningful in a population with limited reproductive potential and often few remaining ART opportunities. Overall, this study provides an important real-world perspective on the use of this gonadotropin combination in routine clinical practice, helping to fill a gap in the current literature, which is largely dominated by randomized controlled trials with strict inclusion criteria. Future well-designed real-world comparative studies involving large multicentre datasets and robust patient stratification will be necessary to directly compare the fixed rFSH/rLH combination with other gonadotropin regimens, including rFSH alone and HP-hMG, and to evaluate efficacy, safety, cost-effectiveness, and patient-centred outcomes.