The relationship between serum progesterone level on the day of HCG trigger in IVF/ICSI cycles and oocyte maturation and embryo quality: a retrospective observational study

Abstract

Purpose

Previous studies have suggested a link between serum progesterone levels on the day of the HCG trigger in IVF cycles and oocyte and embryo quality. This study aims to explore this relationship more thoroughly.

Methods

This study included 496 infertility patients at Moloud Infertility Treatment Center, Zahedan, Iran. Statistical methods were used to assess factors such as oocyte maturation and embryo quality, fertilization rate, BMI, and gonadotropin dosage.

Results

While an initial progesterone cutoff of 1.2 ng/ml was used to perform fundamental analysis, a more accurate cutoff of 1.54 ng/ml was identified, beyond which the average number of M1 oocytes significantly declined. A strong relationship was found between higher progesterone levels and a greater number of retrieved oocytes (p = 0.004), with M1 oocytes showing a similar relation. Also, BMI was significantly related to the quality of eight-cell grade B embryos (p = 0.006). However, no significant correlations were found between progesterone levels and other factors, including patient age (p = 0.327), fertilization rate (p = 0.603), or embryo quality at other stages.

Conclusions

The findings demonstrate that elevated progesterone level, particularly beyond the identified cutoff of 1.54 ng/ml, is a valuable clinical indicator of suboptimal IVF outcomes due to its negative impact on oocyte maturation.

Introduction

Infertility represents a significant family and societal challenge globally. Data from the Human Fertilization and Embryology Authority (HFEA) reveal that the live birth rate (LBR) for in vitro fertilization (IVF) stands at only 26.6% across all age groups [1, 2]. Despite notable advancements in the field of reproductive medicine, the success rate of assisted reproductive technology (ART) cycles hovers around 30–35%. This is in contrast to the expectations of infertile couples who invest considerable financial resources and time, hoping for a substantially higher chance of success [3, 4].

Ovarian stimulation protocols in ART typically employ gonadotropin-releasing hormone (GnRH) agonists or antagonists. These are used to suppress pituitary function and avert the premature surge of Luteinizing Hormone (LH) prior to oocyte retrieval [5]. However, in 5 to 35% of stimulated cycles, there is an observable slight increase in progesterone levels before ovulation onset [5, 6]. The underlying causes of this premature elevation in progesterone (PE) remain unknown. Initial studies titled “Premature luteinization” attributed this PE increase to a premature rise in LH [7, 8]. Subsequent research, however, indicates this phenomenon might also be linked to an upsurge in LH receptor activity within granulosa cells, causing increased PE production even when LH levels remain low [9,10,11].

The importance of progesterone levels on the day of HCG trigger in ART was first noted in 1991 [12]. Progesterone is essential for preparing the uterus lining for embryo implantation by changing it from a growth phase to a secretory phase. However, high progesterone levels during the late follicular phase can disturb the timing between the uterus and the developing embryo, which may lower the chances of successful implantation. This disruption may occur because high progesterone levels affect gene expression in the uterus and reduce its ability to support implantation. While previous studies have shown that early rises in progesterone can negatively affect pregnancy outcomes in IVF, there is still debate about how these increases impact oocyte maturation and embryo quality [13,14,15,16,17,18,19]. This study focuses on how serum progesterone levels on the day of HCG trigger are related to the maturity of oocytes and the quality of embryos. Understanding this relationship could improve how patients are treated during ART cycles and help optimize outcomes.

This study explores the relationship between serum progesterone levels on the day of HCG trigger and critical IVF outcomes, including oocyte maturation and embryo quality. By examining factors such as age, BMI, gonadotropin dosage, and fertilization rates, the research aims to identify patterns that could improve patient care and optimize IVF protocols. Additionally, the study seeks to evaluate the potential of identifying a progesterone cutoff level as a secondary objective, which could provide a practical marker for tailoring ovarian stimulation protocols. Understanding this threshold is essential, as elevated progesterone levels have been associated with suboptimal outcomes in ART. The study also considers how these results align with previous research, emphasizing both the strengths and limitations of the findings, and suggesting directions for future research to enhance our understanding of progesterone’s role in reproductive medicine.

Materials and methods

This retrospective cohort study was conducted to explore the relationship between serum progesterone levels on the day of HCG trigger and IVF outcomes, focusing on oocyte maturation and embryo quality.

Selection of patients

This study retrospectively analyzed 496 women with infertility who were treated at the Moloud Infertility Treatment Centre, Ali Bin Abi Talib Hospital, Zahedan, Iran, from 2019 to 2022. Participants were selected using specific inclusion and exclusion criteria to minimize variability and ensure reliable analysis of the relationship between serum progesterone levels and IVF outcomes.

To determine the sample size, a power analysis was conducted to calculate the minimum sample size required for statistical significance. Based on prior studies examining the effect of progesterone levels on IVF outcomes, a medium effect size (Cohen’s d = 0.5) was assumed. With a significance level (α) of 0.05 and a desired power (1 − β) of 0.80, the minimum sample size required was 88 participants per group for t-tests. A similar calculation for chi-square tests indicated a minimum total sample size of 88 participants. To enhance statistical power and enable subgroup analysis, a total of 496 participants were included, significantly exceeding the minimum requirement and ensuring robust conclusions. Additionally, participants met the following inclusion criteria:

• Women aged 20–42 undergoing their first or subsequent IVF cycles.

• Infertility caused by factors such as poor response to ovulation stimulation, intrauterine insemination (IUI) failure, tubal obstruction, hydrosalpinx, mild endometriosis, or male-factor infertility.

Exclusion criteria were as follows:

• Severe endometriosis.

• Inability to produce at least two mature follicles after stimulation.

• Patients with incomplete records or who withdrew consent.

Severe endometriosis was excluded because it can significantly affect ovarian response, endometrial receptivity, and ART outcomes, introducing confounding variables unrelated to serum progesterone levels. Patients unable to produce at least two mature follicles after stimulation were excluded to ensure that the analysis focused on individuals with sufficient ovarian response, enabling meaningful comparisons. Finally, patients with incomplete records or who withdrew consent were excluded to maintain data quality and ensure the reliability of statistical analyses. These criteria were designed to create a homogenous study population while minimizing confounding factors.

Implementation method

An availability sampling approach was utilized for patient recruitment in this study. Initial hormonal profiling, including follicle-stimulating hormone (FSH), LH, and progesterone, was conducted from the first to the third day of the patients’ menstrual cycles. Ovarian stimulation commenced on cycle day three, employing a regimen of 150–225 units of recombinant FSH (Gonal-F, Serono, Switzerland) and 75 units of human menopausal gonadotropin (HMG, Serono, Switzerland). Following six days of gonadotropin administration, the ovarian response was gauged via ultrasound. If follicular growth reached a diameter of 14 mm, a GnRH antagonist regimen with Cetrorelix (Cetrorelix; ASTA Medica, Amsterdam, The Netherlands; 250 mcg vial) was initiated and the gonadotropin dosage was subsequently adjusted based on ongoing ovarian response assessments. Further follicular development was monitored with an additional ultrasound conducted two days later. Upon identification of at least two follicles measuring 17 mm, ovarian stimulation protocols were concluded, and an ovulatory trigger was achieved with the administration of 10,000 IU of HCG (Choriomon, IBSA Institut Biochimique S.A., Switzerland). Approximately 34–36 h post-HCG administration, oocyte retrieval was performed under general anesthesia, assisted by vaginal ultrasonography. The oocytes were then denuded of cumulus cells and fertilization was undertaken using standard IVF/ICSI techniques. Consistent with the study protocol, the resultant embryos were cryopreserved for subsequent transfer in a following cycle, ensuring optimal conditions for potential implantation.

On the day of HCG administration, serum progesterone levels of all participants were measured using the electrochemiluminescence method (E411, Model: 741 − 0050, Manufacturer: HITACHI, LOT number: 38161201). Based on these measurements, an initial categorization was made with two groups for analysis: Group A, with serum progesterone levels below 1.2 ng/ml [20], and Group B, with levels above 1.2 ng/ml. A thorough comparison was made between the groups using statistical methods, including t-tests for continuous variables, chi-square tests for categorical variables, and regression analysis to account for potential confounding factors. Fundamental characteristics such as age, BMI, baseline serum levels of LH, FSH, and E2 were examined. Additionally, variables associated with ovarian stimulation were analyzed using these statistical methods to assess the relationship between progesterone levels and outcomes such as the quantity and maturity steps of oocytes retrieved, fertilization rates, and the quality of embryo. Later in our findings, we show that the more accurate progesterone cutoff level is 1.54 ng/ml, which has a significant impact on oocyte maturity. While these short-term outcomes are critical for understanding the immediate effects of progesterone levels on ART success, we acknowledge that long-term outcomes, such as live birth rates and miscarriage rates, are not part of this analysis.

Approximately 18–20 h post- IVF/ICSI procedure, oocyte fertilization was assessed. The identification of two pronuclei within the zygote was used as an indicator of successful fertilization. The fertilization rate was then calculated by dividing the number of fertilized oocytes by the total number of oocytes retrieved, with the result expressed as a percentage. On the third day following fertilization, an assessment of embryo quality was performed. Embryos were classified into one of three categories based on specific criteria, which included the count and size of the embryonic cells (blastomeres), the percentage of fragmentation, and the presence or absence of multinucleated cells:

• Grade A (Good Quality): Embryos that have reached the 6 to 8 cell stage, exhibited no fragmentation, and consisted of equally sized blastomeres, signifying optimal development and potential for implantation.

• Grade B (Intermediate Quality): Embryos with 6 to 8 cells, displaying 30–50% fragmentation or heterogeneity in blastomere size, reflecting moderate development.

• Grade C (Poor Quality): Embryos with fewer than 6 blastomeres or exhibiting excessive fragmentation (over 50%) and notable disparities in blastomere dimensions, suggesting suboptimal developmental potential [21].

Following the classification and recording of these embryological parameters, the accumulated data were meticulously inputted into statistical analysis software for comprehensive evaluation.

Data analysis method

All statistical analyses were performed using Statistical Package for the Social Sciences (SPSS), version 22. Statistical tests were selected to examine the relationships between key variables, including serum progesterone levels, oocyte maturity, and embryo quality. Adjustments were made for potential confounders such as age, BMI, and gonadotropin dosage to ensure reliable findings. The following methods were applied:

• Descriptive Statistics: We provided a descriptive overview of the data using means and standard deviations for continuous variables and percentages for categorical variables, offering a clear initial picture of the dataset’s distribution and central tendencies.

• Inferential Statistics: The inferential analysis included:

  • t-tests: Used to compare the means between two groups, analyzing differences in variables such as oocyte maturity and embryo quality across progesterone level groups (e.g., below and above 1.2 ng/ml, later refined to 1.54 ng/ml).

  • Chi-Square (χ²) Tests: Employed to assess relationships between categorical variables, such as progesterone level groups and binary outcomes like successful fertilization.

  • Pearson’s Correlation Coefficient: Applied to evaluate the linear relationship between continuous variables, such as serum progesterone levels and the number of mature oocytes retrieved.

  • Multivariate Regression: Used to adjust for confounders including BMI, age, and gonadotropin dosage, ensuring the relationships observed were statistically valid. Additional multivariate techniques were not deemed necessary as the results were clear and consistent with prior studies.

  • Logistic Regression: Not performed, as the study focused on short-term outcomes such as oocyte maturity and embryo quality rather than binary clinical outcomes (e.g., pregnancy success).

For all statistical tests conducted, a p-value of less than 0.05 was predetermined as the threshold for statistical significance.

Results and key findings

The study population consisted of 496 women undergoing IVF/ICSI cycles. The median age of participants was 31 years (IQR: 28–35), and the median BMI was 24.6 kg/m² (IQR: 22.3–27.5). Participants were divided into two groups based on serum progesterone levels on the day of HCG administration: Group A (progesterone < 1.2 ng/ml; 260 patients) and Group B (progesterone > 1.2 ng/ml; 236 patients). The 1.2 ng/ml threshold was chosen based on prior studies that identified it as a clinically relevant level for assessing the effects of progesterone on IVF outcomes. This cutoff also aligns with our findings, as the range between 1.2 and 1.54 ng/ml showed comparable outcomes in terms of M1 oocyte quality. The median serum progesterone level across the population was 1.02 ng/ml (IQR: 0.69–1.45), with a mean of 1.56 ± 2.50 ng/ml, reflecting substantial variability.

No significant differences were observed in the mean age of participants between Group A (31.62 ± 5.63 years) and Group B (30.86 ± 5.78 years) (P = 0.327). Similarly, BMI did not significantly differ between the groups (P > 0.05). These findings highlight the independence of serum progesterone levels from patient age and BMI, underscoring the heterogeneity in ovarian stimulation responses.

We also looked at other factors like BMI, fertilization rate, the total amount of gonadotropins used, and the number of follicles larger than 17 mm. None of these factors showed significant differences between the two groups (P > 0.05), suggesting that they were not affected by progesterone levels (Table 1). However, there was a notable difference in the number of oocytes retrieved. Group A had an average of 12.73 ± 7.19 oocytes retrieved, while Group B had a higher average of 14.23 ± 8.16 oocytes (P = 0.004). This suggests that higher progesterone levels may positively influence the number of oocytes retrieved, which could be important for improving IVF outcomes.

Table 1 Characteristics of patients stratified by serum progesterone levels (< 1.2 ng/ml vs. >1.2 ng/ml) on the day of HCG injection

Table 2 illustrates that within the patient population observed, the optimal fertilization rates during IVF/ICSI procedures were noted among those with a BMI ranging from 25 kg/m² to 30 kg/m². Nevertheless, the analysis indicated that BMI at the time of serum HCG administration did not significantly influence the fertilization rate, as evidenced by the p-value of 0.625. This suggests that while a BMI in the 25–30 kg/m² range coincided with higher fertilization rates, BMI was not a determinant factor affecting the likelihood of fertilization success in the context of this study.

Table 2 The Relationship between Patient’s BMI level on the day of serum HCG injection and fertilization rate in IVF cycle

As we move to the core objective of our study—examining the relationship between serum progesterone levels on the day of HCG trigger and oocyte maturation and embryo quality—our findings in Table 3 revealed no significant statistical relationship between progesterone levels and the quality of embryos classified as Grade A (6–8 cells, no fragmentation, uniform blastomeres), Grade B (6–8 cells, 30–50% fragmentation, uneven blastomeres), Grade C (fewer than 6 cells, > 50% fragmentation), or embryos with eight cells compared to those with four to six cells. Oocyte quality is classified as GV (germinal vesicle stage, immature), M1 (metaphase I, partially mature), and M2 (metaphase II, fully mature). The serum progesterone levels did not significantly affect the count oocytes in the GV stage (p = 0.883). However, a statistically significant relationship was found between progesterone levels and oocyte maturity at the M1 and M2 stages, with p-values of 0.004 and 0.010, respectively, indicating a clear statistical relationship between progesterone levels and the maturity of oocytes.

Table 3 Relationship between serum progesterone levels and embryo and oocyte quality

As presented in Table 4, our study found no significant correlation between the BMI of patients at the time of serum HCG injection and the development of eight-cell embryos of quality A and C; the differences in outcomes were not statistically meaningful (P > 0.05). However, a significant relation was observed between the patient’s BMI and the incidence of quality B embryos (P = 0.006), indicating that BMI may influence embryo development to some extent. Furthermore, when examining embryos with four to six cells of quality A, B, and C, no significant relation was detected with the BMI on the day of HCG injection (P > 0.05).

Table 4 The determination of the Relationship between the patient’s BMI level on the day of HCG injection in the serum and the quality of eight-cell and four- to six-cell embryos

In Fig. 1, we illustrate the process of determining the cutoff progesterone level at which the average number of M1 oocytes substantially decreases. To achieve this, we sorted the patients by their progesterone levels, with the patient at index 1 having the lowest progesterone level and the patient at index 496 having the highest. The horizontal axis of the figure represents the patient indices, while the vertical axis on the right side corresponds to the progesterone levels (depicted by the red graph). The vertical axis on the left side shows the average number of M1 oocytes.

For each patient index, we used the progesterone level of that patient as a threshold to divide the entire patient population into two groups: Group 1 (patients with progesterone levels lower than the threshold) and Group 2 (patients with progesterone levels higher than the threshold). We then calculated the average number of M1 oocytes for each group and plotted these values as two separate lines in the figure—the blue line represents Group 1 and the green line represents Group 2.

The critical point of interest is where the green line (Group 2) dips below the blue line (Group 1), indicating that the average number of M1 oocytes in patients with higher progesterone levels (Group 2) becomes lower than in patients with lower progesterone levels (Group 1). This marks the progesterone cutoff level where a noticeable decline in oocyte maturity begins. In Fig. 1, this cutoff occurs at patient index 463, corresponding to a progesterone level of 1.54 ng/ml.

In discussion section, we will explain how our finding of a cutoff progesterone level of 1.54 ng/ml aligns with previous studies that have also identified a critical threshold where progesterone begins to negatively affect oocyte maturation and embryo quality. Our findings further emphasize the importance of monitoring progesterone levels closely in IVF cycles to optimize oocyte retrieval outcomes. By confirming a cutoff at 1.54 ng/ml, our study adds to the growing body of evidence that excessive progesterone levels can impair oocyte maturity, providing clinicians with a practical threshold to consider in tailoring ovarian stimulation protocols.

Thus, our analysis identifies 1.54 ng/ml as the cutoff progesterone level, after which the average number of M1 oocytes starts to decline significantly, reinforcing previous research and providing a critical threshold for understanding the impact of progesterone levels on oocyte maturity in IVF cycles.

Fig. 1

Relationship between the average number of M1 oocytes and serum progesterone levels

Figure 2 illustrates the ROC curve used to evaluate the diagnostic performance of progesterone levels in predicting oocyte maturity. The curve quantifies the ability of serum progesterone levels to distinguish between patients with higher and lower probabilities of having M1 quality oocytes.

The light blue region highlights the “Intersection Zone,” where progesterone levels range from 1.2 to 1.54 ng/ml. In this range, the blue and green lines in the main findings intersect, indicating similar average numbers of M1 oocytes for patients in both groups. The ground truth data show a gradual increase in the probability of having at least one M1 oocyte, starting from 50% at 1.2 ng/ml and reaching 95% as progesterone levels approach 1.54 ng/ml. The AUC value of 0.89 confirms that serum progesterone levels provide a strong predictive capability for oocyte maturity outcomes, particularly when the progesterone level exceeds 1.54 ng/ml, where a noticeable decline in M1 quality oocytes is observed. This figure supports the identified threshold and its clinical relevance for tailoring IVF protocols.

Fig. 2

ROC Curve for Predicting Oocyte Maturity Based on Progesterone Levels

Discussion

The key finding of our study was the identification of a specific progesterone cutoff level of 1.54 ng/ml, beyond which the average number of M1 oocytes significantly decreases. This threshold was determined using a novel analytical method and carries important clinical implications for tailoring ovarian stimulation protocols in IVF cycles. Progesterone is a hormone that prepares the uterine lining for implantation and subsequent mating [22, 23]. During the IVF cycle, proper timing of the progesterone surge is necessary for the readiness of the endometrium for implantation and to maintain synchronization between the embryo and the endometrium. In this way, many women undergoing the IVF cycle, are prescribed medications to reduce pituitary gonadotropin secretion to prevent premature increase of luteinizing hormone and serum progesterone increase. However, there is limited information about the effect of progesterone levels on the maturity of oocytes and the quality of embryos [24,25,26]. In this study, we specifically focused on the relationship between progesterone levels on the day of HCG trigger and various clinical parameters, such as age, BMI, fertilization rate, gonadotropin dosage, number of follicles above 17 mm, oocytes maturation and the quality of embryos. These findings have important clinical implications for managing ovarian stimulation in IVF cycles. Identifying a progesterone cutoff level of 1.54 ng/ml provides clinicians with a practical marker to tailor treatment protocols. Regular monitoring of serum progesterone levels, particularly on the day of HCG administration, allows timely adjustments to gonadotropin dosages or HCG timing to maintain progesterone below this threshold, optimizing oocyte quality. For patients exceeding this level, clinicians might implement strategies such as reduced gonadotropin doses, dual-trigger protocols, or freezing all embryos for subsequent transfer to improve implantation potential. The 1.54 ng/ml cutoff also serves as a decision point for modifying stimulation protocols in real-time, enabling proactive management of hormonal imbalances. Additionally, this threshold enhances patient counseling by offering a concrete basis to discuss risks associated with elevated progesterone, expected outcomes, and potential adjustments in treatment plans. These practical applications of the cutoff provide a clear framework for improving oocyte maturation, embryo quality, and overall IVF outcomes through precise hormone management and individualized care.

Our findings indicate that on the day of HCG injection, progesterone levels were not linked to the age or BMI of patients. This is consistent with previous research by Mehrafza et al. [26] and Pouget et al. [27], which also found no notable connection between the day’s progesterone levels and patient age. Moramezi et al. [28] expanded on this, showing no significant correlation between progesterone levels and a range of demographic and clinical factors, including live birth outcomes, delivery method, infertility duration, previous IVF outcomes, and reasons for infertility. Moreover, our data suggest that while patients with a BMI in the range of 25 to 30 had the highest fertilization rates, BMI itself was not a decisive factor for fertilization success in the IVF/ICSI process. Z Petanovski et al.‘s research highlighted that an increase in BMI can significantly reduce the chance of an IVF cycle, with clinical pregnancy rates dropping from 49.2% in individuals of normal weight to 34.3% in those who are overweight [29]. Our study aligns with this finding to some extent, showing a trend where the average fertilization rate during IVF/ICSI cycles was higher in groups with lower progesterone levels compared to those with higher levels, although this trend did not reach statistical significance.

Our study has identified a critical progesterone cutoff level of 1.54 ng/ml, beyond which the average number of M1 oocytes significantly decreases. This precise threshold provides a valuable clinical marker for optimizing IVF outcomes. By identifying 1.54 ng/ml as the point where oocyte maturation starts to decline, our findings verify previous research that suggested elevated progesterone levels could negatively impact fertilization rates and oocyte quality. The study by Saharkhiz et al. [30] supports this observation, indicating that a serum progesterone level above 1.5 ng/ml on the day of HCG injection correlates with lower fertilization rates compared to levels below 1.5 ng/ml. Mehrafza et al. [26] also reported a similar pattern, where high serum progesterone was associated with reduced fertilization rates. Our findings verify this understanding by pinpointing 1.54 ng/ml as a more precise cutoff, beyond which M1 oocyte significantly declines. This threshold offers clinicians a critical marker for optimizing ovarian stimulation protocols and improving IVF outcomes. Both our study and related literature suggest that elevated progesterone levels could be detrimental to fertilization and, consequently, the chances of achieving pregnancy in IVF treatments. Although a notable inverse relationship between serum Progesterone on the day of hCG triggering and the success of IVF is established in many studies, its endocrinologic mechanism is unknown. It has been described in many studies that it may involve as an ovarian event, with negative effects on oocyte maturation, fertilization, or early embryonic development [31].

Studies indicated the serum progesterone elevation during follicular phase is not always prevented by LH suppression which is seen in up to 30% of COH cycles. Many hypotheses may be considered to explain this phenomenon like two-cell, two-gonadotropin theory in biosynthesis of estrogen. granulose cells by means of FSH contribute to conversion of cholesterol to progesterone, which is convert to androgens under the influence of LH in thecal cells. These androgens are then passed to the granulose cells to produce estrogens. In COH cycles due to the increased number of follicles with 17 mm or a possible LH effect from exogenous gonadotrophins granulose cells sensitivity to FSH is increased. the rising oestradiol levels may induce increased LH secretion sufficient to stimulate granulose cells to produce progesterone but inadequate to trigger ovulation. Studies showed beyond the optimal standard of final oocyte maturation the duration of COH should not be prolonged. On this point, a personalized therapy is the key factor to ovarian stimulation in IVF/ICSI cycles, which means to select the appropriate gonadotropin dose according to the patient’s BMI and ovarian reserve, and to adjust the gonadotropin dose according to follicular development and hormone levels during stimulation [7, 31, 32].

Furthermore, our study found a significant statistical relationship between progesterone levels on the day of HCG administration and the number of oocytes retrieved. Saharkhiz et al.‘s research offers an interesting comparison, showing that patients with progesterone levels below 1.5 ng/ml had an average oocyte count of 7, while those with levels above 1.5 ng/ml had an average count of 8 [30]. In line with this, our data showed that progesterone levels above 1.54 ng/ml were associated with a significantly higher number of oocytes retrieved, underlining a strong relationship between elevated progesterone levels and oocyte yield in our cohort.

Consistent with the work of Mehrafza et al. [26], our study observed a higher number of oocytes retrieved in patients with elevated progesterone levels. This also aligns with findings from Vikas et al. [33], who reported a significantly larger average number of oocytes collected from patients with progesterone levels above 1.5 ng/ml compared to those with lower levels. Furthermore, Aflatoonian et al. [34] identified a significant correlation between progesterone levels and the number of metaphase 2 oocytes, yet found no impact on the rate of fertilization, which is also reflected in our findings. By pinpointing the cutoff of 1.54 ng/ml, our study verifies these earlier observations and provides further clinical relevance.

In our investigation, the amount of gonadotropin used did not show a significant statistical link with progesterone levels measured on the day of HCG administration. However, participants with progesterone levels above 1.2 ng/ml tended to use higher gonadotropin doses. This observation aligns with findings from Vikas et al., who also reported that higher progesterone levels were associated with a higher gonadotropin dosage, echoing the patterns seen in our study [33].

Additionally, our results indicate no statistically significant correlation between serum progesterone levels on the day of HCG administration and the quality of embryos, classified from grades A to C, at the 4 to 6 cell and 8 cell stages. However, Huang et al. [35] have highlighted a negative influence of elevated progesterone levels on both the day of HCG injection and on embryo quality, regardless of the baseline FSH, total gonadotropin dose, age of the woman, or duration of ovarian stimulation. This suggests that an increase in progesterone levels beyond 2.0 ng/ml prior to oocyte maturation could adversely affect oocyte and embryo development, a conclusion that is in line with the outcomes of our research, indicating potential negative implications of raised progesterone levels for the oocyte maturity and embryo quality.

In our investigation, the quality of embryos with eight cells (grade B) showed a significant association with the patients’ BMI, suggesting that increasing BMI levels do not negatively influence embryo quality across the board. This finding stands in contrast to a comprehensive analysis by Xiang Liu et al., which indicated that higher BMI is correlated with inferior IVF results, such as a reduced number of oocytes collected, fewer viable embryos, and a higher rate of fetal abortion in women with a BMI of 30 kg/m2 or higher [36].

Moreover, in our study, there was a statistically significant association between serum progesterone levels on the day of HCG administration and retrieving of oocytes at the M1 and M2 stages. However, no such relationship was found for oocytes at the GV stage. These results differ from those reported by Saharkhiz et al. [30], where the number of oocytes showed no significant variance between groups with differing progesterone levels. The discrepancy could be attributed to the smaller sample size in our study compared to that of Saharkhiz’s, suggesting that our findings might be influenced by the scale of the population.

This study is retrospective, so it cannot fully prove that higher progesterone levels cause changes in oocyte maturity. Other factors, like ovarian response or stimulation protocols, might affect progesterone levels. However, our results align with previous studies, and the identification of the 1.54 ng/ml cutoff supports the importance of progesterone levels in IVF outcomes. Future studies that follow patients over time are needed to confirm these findings and better understand the causes of these effects. Clinically, the identification of a 1.54 ng/ml progesterone threshold offers practitioners a valuable marker for tailoring ovarian stimulation protocols. By adjusting medication dosages to maintain progesterone levels below this cutoff, clinicians can potentially improve oocyte maturation and, by extension, the overall success of IVF cycles. This finding encourages a more individualized approach to hormone regulation during IVF, which could optimize outcomes for a wide range of patients. Elevated progesterone levels during controlled ovarian hyperstimulation may disrupt the hormonal balance essential for oocyte maturation and endometrial receptivity. Increased granulosa cell sensitivity to gonadotropins can prematurely activate progesterone receptors, impairing oocyte meiotic progression and cytoplasmic maturation. Additionally, progesterone elevation may desynchronize the endometrium and embryo development, compromising implantation potential. The identified cutoff of 1.54 ng/ml marks the threshold where these disruptions begin to significantly impact oocyte quality, underscoring the importance of maintaining hormonal balance during ovarian stimulation to optimize IVF outcomes.

While this study provides valuable insights into the impact of serum progesterone levels on oocyte maturity and embryo quality, several limitations must be acknowledged. First, the focus on short-term outcomes, such as oocyte maturation and embryo quality, without evaluating long-term outcomes like live birth or miscarriage rates, limits the scope of clinical applicability. Second, the study population was derived from a single center, which may affect the generalizability of the findings. Additionally, the retrospective design of the study precludes establishing causal relationships and may be subject to unmeasured confounders. Finally, while the identified progesterone cutoff of 1.54 ng/ml is clinically significant, it lacks external validation, and the underlying biological mechanisms were not directly measured. Future multicenter studies with larger cohorts and long-term follow-up are needed to validate these findings and explore their broader clinical relevance.

In summary, our study provides new insights into the impact of progesterone levels on oocyte maturity, particularly identifying 1.54 ng/ml as a critical cutoff. This finding not only aligns with previous research but also refines the understanding of progesterone’s role in IVF outcomes, offering clinicians a more precise threshold for decision-making. Future studies should aim to replicate these findings with larger sample sizes and explore the mechanisms by which progesterone influences oocyte and embryo quality at different stages of maturation. This will enhance our understanding of how to optimize hormone regulation in IVF treatments and improve the chances of success for patients.

Conclusion

The results of this study shed light on the complex relationship between serum progesterone levels and IVF success, with a focus on oocyte maturity and embryo quality. Our findings identified a critical progesterone cutoff level of 1.54 ng/ml, beyond which the average number of M1 quality oocytes significantly decreases. This threshold provides an important marker for clinicians, indicating that elevated progesterone levels are associated with reduced oocyte maturation and may be a predictor of suboptimal outcomes in IVF cycles.

Although the study did not find significant relationships between progesterone levels and variables such as patient age, BMI, or the overall fertilization rate, the analysis revealed a clear decline in M1 oocytes as progesterone levels exceeded the 1.54 ng/ml threshold. Additionally, progesterone levels did not significantly affect embryo quality across the different classifications (A, B, C), indicating that the hormone’s effect may be more concentrated on oocyte maturation rather than later stages of embryo development.

This nuanced understanding suggests that elevated progesterone levels serve as a potential marker for suboptimal IVF outcomes, particularly in terms of oocyte maturity. The identification of the 1.54 ng/ml cutoff provides a valuable tool for clinicians to refine ovarian stimulation protocols, ensuring that progesterone levels are carefully monitored to optimize the number of mature oocytes retrieved and improve overall treatment success. Individualized hormone management is essential in enhancing IVF outcomes and personalizing care for patients.

While our study provides evidence supporting the 1.54 ng/ml cutoff, its retrospective design limits definitive conclusions about causality. Larger-scale studies are needed to confirm these findings across more diverse populations. Future research with broader patient cohorts could help validate this threshold further and explore its applicability in different clinical settings, especially in terms of varying ovarian stimulation protocols. Investigating whether the cutoff holds in populations with different hormonal profiles will be key to understanding the full impact of progesterone on oocyte maturation and embryo quality. By addressing these questions, future studies can help refine hormone regulation strategies in IVF treatments and further improve patient outcomes.