In this study, we investigated the predictive indicators for determining the optimal FSH starting dose in patients undergoing superovulation treatment with the EFDGA protocol and constructed a nomogram prediction model. This method allowed the automatic assessment of FSH starting dose in patients using female age, BMI, baseline FSH, AMH, and AFC which were basal clinical parameters as inputs. To evaluate the method, the nomogram was trained using the data from center 1, and independent testing was conducted using test sets from both internal and external centers separately. Model reliability was confirmed in the training and both internal and external validation sets using Bland and Altman plots and paired t- test.
In ART cycles, the primary objective of ovarian stimulation is to induce the development of multiple follicles, thereby obtaining an optimal quantity of viable oocytes to enhance the pregnancy rate. According to the follicular threshold concept proposed by Brown (21), elevating FSH concentration above the threshold by 10–30% is sufficient to stimulate normal follicular development. Exogenous supra-physiological levels of FSH play a crucial role in inducing the development of multiple follicles, allowing the recruited follicles to continue maturing. However, there is significant variability in the FSH sensitivity threshold among individuals. Our study revealed that the appropriate FSH initiation dose is not only correlated with age and parameters reflecting ovarian reserve such as AMH, bFSH, and AFC but also associated with BMI. The use of FSH initial doses in the long-acting protocol for the follicular phase currently lacks consensus and guidelines among experts.
Due to the advantages of the EFDGA protocol, characterized by high endometrial receptivity in fresh cycles, a gentle step-up approach is commonly employed. Although this may reduce the average number of retrieved oocytes, there is a significant improvement in fertilization rates (2PN), embryo implantation, clinical pregnancy, and high-quality embryo formation (22). However, for patients whom initial FSH dose does not reach the threshold or who exhibit a suboptimal ovarian response, timely adjustment of FSH dosage during the stimulation process is equally crucial. Hence, we selected an inclusion criterion of FSH increment dosage less than 75IU. Several studies have confirmed that obtaining 15 oocytes maximizes live birth rates in fresh embryo transfer cycles (23). Steward et al., analyzing 256,381 cycles, identified that retrieving more than 15 oocytes was the optimal predictor for the risk of OHSS (24). In studies of long-acting protocols, various centers have suggested that the range of retrieved oocytes between 10 − 17 and 6 − 20 achieves satisfactory clinical pregnancy rates and lower rates of severe OHSS in fresh embryo transfer cycles(25, 26), thereby reducing the time to achieving a live birth. Therefore, in this study, we defined the optimal oocyte retrieval range as 8 − 15.
Several formulas or models predicting FSH initiation doses for different ovarian stimulation protocols have been reported globally. Antonio La Marca et al. (27) identified three relevant factors (age, AFC, FSH) and developed a nomogram for predicting FSH initiation doses. Unfortunately, their study focused on the luteal phase protocol, employing a step-down dosage pattern. Additionally, due to ethnic differences, this model may not apply to the Chinese population. In China, two studies have investigated FSH initiation doses for patients using antagonist protocols (16, 28), but they primarily targeted patients with polycystic ovary syndrome (PCOS) rather than those with normal or low ovarian reserve. PCOS, characterized by high ovarian reserve and response, makes their model unsuitable for patients with normal or low ovarian reserve. Our multifactorial regression model revealed that patient age, BMI, basal FSH, AMH, and AFC are essential reference factors for FSH initiation doses, aligning with clinical knowledge. Additionally, some earlier studies that used AMH or AFC alone predicting ovarian reserve(29) or nomograms that did not include BMI as a variable (30, 31) are consistent with our findings.
Age has long been under scholarly discussion as a predictor for the initiation dose of gonadotropin (FSH) in ART. The decline in fertility with age is primarily characterized by a reduction in the number of follicles, a diminished response of the ovaries to exogenous gonadotropin, and a significant decrease in pregnancy and live birth rates. To address these physiological changes, ovarian stimulation typically employs high-intensity FSH stimulation for elder individuals, while younger individuals with high ovarian reserves may require more precise low-dose FSH stimulation. The positive correlation trend with age in this model aligns with previous research (32, 33). Interestingly, some predictive models do not incorporate age as a factor, potentially due to their target population being PCOS patients who generally possess higher ovarian reserves. In such cases, bLH may have a more pronounced impact on FSH initiation doses than age (34). Alternatively, models using the PPOS protocol may diminish the influence of age by initiating FSH more intensively (17).
This study confirms a close correlation between FSH initiation doses and ovarian reserve. The decrease in ovarian reserve was manifested by a reduction in AFC and an elevation in FSH levels. This finding aligns with expressions in other models (17, 27). Recently, AMH has been considered more accurate than basal FSH in predicting ovarian reserve and is widely recognized as one of the simplest, most sensitive, and reliable indicators for evaluating ovarian reserve (35). There is generally a positive correlation between AMH and AFC, although some studies show a 30% inconsistency between the two indicators(36, 37). In clinical practice, predicting ovarian responsiveness with a single parameter is challenging. Therefore, clinicians often conduct multiple assessments and utilize predictive models combining various parameters to enhance the effectiveness of predicting ovarian responsiveness. In contrast to the study by Simanfei (34), we did not include LH as an influencing factor after multifactorial analysis in this study. The rationale behind this decision lies in the diverse characteristics of the included populations, with some PCOS patients exhibiting significantly higher LH levels than FSH. However, in the general population, no such inclination in baseline LH levels was observed. This aligns with the consistent exclusion of LH as a modeling factor in most studies involving the general population.
We observed a significant correlation between BMI and the initiation dose of gonadotropin (FSH). Body weight is one of the factors that can interfere with the secretion of gonadotropins, and obesity is associated with ovarian dysfunction (38). The serum levels of gonadotropins entering the body are directly influenced by body weight. Therefore, body weight is also considered an indicator for predicting the initial dose. Some studies indicate that, compared to weight and body surface area, BMI is a more important factor for predicting the number of retrieved oocytes (34). BMI specifically influences the adjustment of ovulation-inducing drugs in patients with PCOS (39) and pregnancy and live birth outcomes (40).
Recently, nomograms have been applied in various fields of reproductive medicine to predict the likelihood of human embryo euploidy (41, 42), oocyte retrieval(43), fertilization failure(44), as well as predicting live birth rates for different types of patients seeking fertility assistance (45) (46). Drawing a nomogram to predict ovarian response and the optimal FSH initiation dose is a simple, efficient, and feasible approach. To our knowledge, this study is the first to develop a nomogram for predicting the FSH initiation dose in the EFDGA protocol.
The strength of this model lies in the precise construction of a nomogram for the initiation dose of FSH based on clinical and biological variables. This nomogram is designed for individualized prediction of the initial FSH dose in patients outputting with normal responses undergoing IVF/ ICSI. The model is weighted, considering the different weights of various predictive factors, enabling a more objective and personalized prediction of the FSH initiation dose. Furthermore, this study had an ample sample size, and both internal and external validations were conducted, indicating the model's stable predictive value. The factors included in this model are straightforward and easily measurable in clinical practice. This suggests that the model has good clinical predictive value and is easily applicable in clinical settings. The results of this study are poised for straightforward clinical implementation and hold promise for wider clinical adoption.
However, this study has several limitations. First, ovarian responsiveness is largely influenced by individual factors, and the polymorphism of FSH and its receptor genes is crucial for the individualized use of FSH doses in treatment plans. Patients with similar baseline characteristics may exhibit significant differences in response to gonadotropin drugs. Due to the limited clinical adoption of genetic receptor polymorphism testing, this aspect was not thoroughly analyzed in this study. Second, the advantage of the long protocol for the early follicular phase lies in achieving a higher pregnancy rate with fresh cycle embryo transfer. However, this study included patients with 8 − 15 retrieved eggs as modeling criteria without considering the maturity of eggs, embryo quality, and pregnancy outcomes. Therefore, the predictive value of this model for pregnancy outcomes is limited. Third, the FSH used in this study included recombinant human follicle-stimulating hormone alpha (Merck Serono SA Aubonne Branch, Switzerland), recombinant human follicle-stimulating hormone beta (Merck Sharp & Dohme, USA), and urinary follicle-stimulating hormone (Livzon Pharmaceutical Group, China). These drugs may have varying biological potencies, which could impact the model results. Finally, different laboratories may use different methods to measure AMH levels, and various assay methods have different specificities and sensitivities, potentially affecting the generalizability of this model.