Objective:To investigate the influencing factors and perinatal outcomes associated with monozygotic twins (MZT) following elective single embryo transfer (eSET) via in vitro fertilization or intracytoplasmic sperm injection and embryo transfer (IVF/ICSI-ET). Methods:A retrospective cohort study was conducted on 12 079 patients who achieved pregnancy after undergoing IVF/ICSI-eSET at Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University between January 2015 and September 2023. Patients were stratified into two groups based on ultrasound findings 30 d post-transfer: singleton pregnancy group and MZT pregnancy group. Finally, 300 MZT and 1 500 single pregnancies, which were randomly matched according to 1∶5 were included by study period. General patients' characteristics, embryo-related factors, and perinatal outcomes were compared between the two groups. A multivariate logistic regression model was employed to identify risk factors for MZT after single embryo transfer, adjusting for potential confounding variables.Results:The incidence of twin pregnancy following single embryo transfer was 2.48% (300/12 079), which was higher than that of naturally conceived monozygotic twin pregnancy. No significant difference was found in baseline characteristics between the two groups (all P>0.05). The blastocyst transfer rate was higher in the MZT pregnancy group [93.3% (280/300)] than in the singleton pregnancy group [88.8% (1 332/1 500), P=0.022]. Multivariate logistic regression analysis also showed that blastocyst transfer was associated with an increased risk of MZT ( OR=0.552, P=0.016, 95% CI: 0.341-0.894). Analysis of blastocyst cycles showed that the risk of MZT was higher when transferring high-quality blastocysts [79.6% (223/280) vs. 67.8% (903/1 332), P<0.001], where as a trophectoderm (TE) grading of C [20.4% (57/280) vs. 32.2% (429/1 332), P<0.001] had a lower risk of MZT. After adjusting for confounding factors, the risk of MZT was found to increase with the transfer of blastocysts with a B-grade inner cell mass (ICM) ( OR=0.601, P=0.001, 95% CI: 0.442-0.819) and A/B grade TE (grade A: OR=2.951, P<0.001, 95% CI: 1.980-4.399; grade B: OR=1.840, P<0.001, 95% CI: 1.315-2.576). The risk of complications during pregnancy [47.7% (143/300) vs. 19.3% (289/1 500), P<0.001], preterm labor [55.1% (140/254) vs. 7.4% (101/1 368), P<0.001], and the risk of stillbirth [3.7% (11/300) vs. 1.5% (22/1 500), P=0.016] were significantly higher in the MZT pregnancy group than in the singleton pregnancy group. Conclusion:Assisted reproductive technology may contribute to the risk of MZT. Transfer of blastocysts, particularly those with loose ICM arrangement and dense TE arrangement, appears to increase the risk of MZT in patients undergoing eSET.

Objective:To explore the effectiveness, safety, and cost among urinary follicle-stimulating hormone (u-FSH), recombinant FSH (r-FSH)α, and r-FSHβ in the early follicular phase prolonged protocol for patients under 35 years old with normal ovarian function.Methods:It was a retrospective cohort study. Patients under 35 years old with normal ovarian function who underwent early follicular phase prolonged protocol for ovulation stimulation and using in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) for fertilization in Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University from January 2018 to December 2023 were recruited, including the fresh and frozen-thawed embryo transfer (FET) cycles. Patients were divided into u-FSH group, r-FSHα group, and r-FSHβ group. A total of 1 048 ovarian stimulation cycles were included, with 150 cycles, 490 cycles and 408 cycles in the three groups respectively. A total of 710 FET cycles with fresh cycle cancellation were included, with 95 cycles, 320 cycles and 295 cycles in the three groups respectively. The baseline data, pregnancy outcomes, safety, and cost were compared among the three groups. The main observation indicators were cumulative pregnancy rate and cumulative live birth rate (CLBR). A binary logistic regression model was used to control confounding factors, and to analyze the relationship between three ovulation inducing medicine and CLBR. Results:The difference in the number of oocytes retrieved among the u-FSH group, r-FSHα group, and r-FSHβ group was statistically significant [13.0 (10.0, 16.0), 14.0 (11.0, 18.0), 15.0 (11.0, 19.0), respectively, P=0.012], and the difference in the number of 2PN embryos was statistically significant [9.0 (6.0, 12.0), 10.0 (7.0, 13.0), 10.0 (7.0, 13.0), respectively, P=0.046]. There were no statistically significant differences in the number of available embryos, available embryo rate, the number of high-quality embryos, high-quality embryo rate, available blastocyst formation rate, fresh cycle clinical pregnancy rate, live birth rate in fresh cycle, cumulative pregnancy rate of frozen embryos with fresh cycle cancellation, CLBR of frozen embryos with fresh cycle cancellation, cumulative clinical pregnancy rate, CLBR, moderate to severe ovarian hyperstimulation syndrome incidence, ectopic pregnancy rate, multiple pregnancy rate and neonatal malformation rate among the three groups (all P>0.05). In terms of economy, the u-FSH group had the lowest total gonadotropin cost for each patient, while the r-FSHα group had the highest. The differences among the three groups were statistically significant [u-FSH group 4 429.08 (3 198.78, 5 044.23) yuan, r-FSHα group 6 023.72 (5 433.75, 7 529.65) yuan, r-FSHβ group 5 480.00 (4 550.90, 6 437.86) yuan, P<0.001]. Binary logistic regression analysis was conducted, using u-FSH as a control. The CLBR of the r-FSHα group and r-FSHβ group showed no statistically significant difference compared with the u-FSH group (a OR=0.95, 95% CI: 0.57-1.58, P=0.838; a OR=0.89, 95% CI: 0.54-1.48, P=0.654). Conclusion:For patients under 35 years old with normal ovarian function undergoing long protocol ovarian stimulation, the effectiveness and safety of the three ovarian-stimulating medicine are similar, but u-FSH has economic advantages.

Objective:To investigate whether malignant tumors affect the laboratory outcomes of patients in their first controlled ovarian hyperstimulation (COH) cycle.Methods:This study was a retrospective case-control study that analyzed the clinical and laboratory data of patients who underwent fertility preservation before chemotherapy and radiotherapy due to malignant tumors, as well as patients with infertility caused by tubal factors who first underwent in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) at the Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University from January 2020 to May 2024. Patients who underwent fertility preservation were designated as the research group, while patients who underwent assisted reproduction due to tubal factors during the same period were designated as control group. After 1∶3 propensity score matching (PSM), 40 patients were included in the research group and 118 patients were included in control group. The ovarian response, oocyte retrieval outcomes, and embryonic development after fertilization in the first COH cycle were compared between the two groups. Results:After PSM, the research group and control group showed statistically significant differences in the gonadotropin (Gn) starting dosage [225.00 (162.50, 300.00) U vs. 193.75 (150.00, 225.00) U, P=0.002], duration of Gn used [10.00 (8.00, 11.00) d vs. 12.00 (10.00, 13.00) d, P<0.001], and average estradiol levels on human chorionic gonadotropin trigger day [2 487.00 (1 461.25, 4 090.25) pmol/L vs. 10 738.50 (8 400.00, 16 507.25) pmol/L, P<0.001]. However, no statistically significant difference was found in the total dosages of Gn used between the two groups ( P>0.05). There were no significant differences between the groups in terms of the number of oocytes retrieved, the number of metaphase Ⅱ oocytes, two pronuclei (2PN) rate, 2PN cleavage rate, available embryo rate, high-quality embryo rate, blastocyst formation rate, and available blastocyst formation rate (all P>0.05). Conclusion:Compared with infertility patients with tubal factors, there is no significant difference in the laboratory outcomes of malignant tumor patients undergoing COH for fertility preservation prior to chemotherapy and radiation.

Objective:To investigate the impact of different luteal phase support protocols on pregnancy outcomes in patients aged ≤35 years undergoing modified natural cycle frozen-thawed embryo transfer (mNC-FET).Methods:A retrospective cohort study was conducted to analyze 2 086 cycles of patients aged ≤35 years who received mNC-FET cycles in Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University from January 2018 to December 2020. The cycles were divided into three groups based on luteal phase support protocols used. The patients received a combination of progesterone soft capsule and dydrogesterone in the group A (446 cycles), the patients received dydrogesterone in the group B (439 cycles), and the patients received a combination of progesterone vaginal sustained-release gel and dydrogesterone in the group C (1 201 cycles). The pregnancy and perinatal outcomes were compared between groups A and B, groups C and B after matching the baseline data in a ratio of 1∶1 using the propensity score matching (PSM). The effect of different luteal phase support on live birth rate was analyzed after adjusting for confounding factors affected by univariate and multivariate generalized estimating equation (GEE).Results:After PSM, there were no significant differences between groups A and B, groups C and B in human chorionic gonadotropin positive rate, clinical pregnancy rate, ectopic pregnancy rate, live birth rate in transplant cycle, incidence of low weight, macrosomia, premature delivery rate, pregnancy complication rate and incidence of birth defects (all P>0.05). GEE analysis showed that three different luteal phase support regimens were not associated with live birth rate. Conclusion:In the mNC-FET cycle, patients aged ≤35 years who chose dydrogesterone alone as luteal phase support drug, had no difference in live birth rate and perinatal outcome between progesterone soft capsules or progesterone vaginal sustained-release gel combined with dydrogesterone, but the outcome still needs to be confirmed by large sample prospective studies.

Objective:To investigate whether hysteroscopic transcervical resection of septum (TCRS) prior to in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) can improve cumulative live birth rates in patients with uterine septum. Methods:A retrospective cohort study was conducted to analyze data from 244 patients with partial uterine septum who underwent IVF/ICSI at the Reproductive Medicine Center of the Third Affiliated Hospital of Zhengzhou University between January 2016 and August 2022. The patients were divided into a surgical group ( n=171) and a non-surgical group ( n=73) based on whether TCRS was performed prior to IVF/ICSI. The clinical outcomes of IVF/ICSI in the two groups were analyzed, with the primary observation indicator being the cumulative live birth rate. Cox regression analysis was employed to identify determinants. Results:The age of patients in the operated group [(31.20±3.80) years] was younger than that in the non-operated group [(32.92±5.34) years, P=0.005], and the basal antral follicle count [17.0 (11.0, 24.0)] was higher than that in the non-operated group [14.0 (8.0, 21.5), P=0.039]. There were no significant differences in other baseline data (all P>0.05). The cumulative pregnancy rate [79.53% (136/171)] and the cumulative live birth rate [60.23% (103/171)] in the operated group during the 24-month follow-up period were significantly higher than those in the non-operated group [65.75% (48/73), P=0.022; 45.21% (33/73), P=0.030]. Compared with the operated group [296.0 (260.0, 430.0) d], the duration from the start of ovarian stimulation to the first live birth was significantly prolonged in the non-operated group [379.0 (329.5, 471.5) d, P<0.001]. Adjusted Cox-regression analysis showed that whether or not surgery was performed ( HR=1.683, 95% CI: 1.116-2.539, P=0.013) and the basal antral follicle count ( HR=1.032, 95% CI: 1.000-1.065, P=0.048) were independent factors affecting cumulative live birth rate. Conclusion:Performing TCRS before IVF/ICSI can improve cumulative live birth rates of patients with uterine septum.

Objective:To investigate the effects of male body mass index (BMI) on semen parameters and perinatal outcomes following artificial insemination by husband (AIH) treatment.Methods:A retrospective cohort study was conducted to analyze the clinical data of 5 053 patients underwent AIH treatment at the Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University, from January 2017 to February 2024. The study focused on factors such as male semen parameter abnormalities, male sexual dysfunction, female cervical factors, reproductive tract malformations, and unexplained infertility. Patients were classified into three groups based on male BMI: normal weight group (18.5-23.9 kg/m2, n=1 673), overweight group (24.0-27.9 kg/m2, n=2 078), and obese group (BMI≥28.0 kg/m2, n=1 302). The primary objective was to assess the differences in semen parameters and perinatal outcomes among the three groups. Multivariable logistic regression and linear regression analyses were applied to adjust for potential confounders that could influence semen parameters and perinatal outcomes. Results:Semen volume in the normal weight group and overweight group [4.00 (3.00, 5.50) mL, 4.00 (3.00, 5.50) mL] was higher than that in the obese group [4.00 (3.00, 5.00) mL], with a significant difference among the three groups ( P<0.001, a P<0.001). The total sperm count in the normal group and overweight group [207.60 (121.90, 341.75)×10 6, 211.80 (119.88, 334.83)×10 6] was higher than that in the obese group [188.40 (110.96, 323.41)×10 6], with a significant difference among the three groups ( P=0.007, a P<0.001). The total progressive sperm motility count in the normal group [88.18 (43.63, 163.80)×10 6] was higher than that in the obese group [75.30 (40.29, 147.86)×10 6], with a significant difference among the three groups ( P=0.001, a P<0.001). The percentage of forward motile sperm in the normal group [(45.37±17.16)%] was higher than that in the overweight group [(44.03±17.36)%] and the obese group [(43.80±17.21)%], with a significant difference compared among the three groups ( P=0.020, a P=0.016]. In terms of perinatal outcomes, after multivariate logistic regression analysis, only the overweight and obese groups had higher newborn birth weights [(3 389.53±472.65) g, (3 408.57±507.90) g] compared with the normal group [(3 271.32±532.02) g], with a significant difference among the three groups ( P=0.010, a P=0.009). Conclusion:Higher male BMI is associated with decreased semen quality and may increase newborn birth weight following AIH treatment.

Objective:To investigate the association between homocysteine (Hcy) and recurrent pregnancy loss (RPL), as well as its impact on clinical pregnancy outcomes in patients undergoing in vitro fertilization/intracytoplasmic sperm injection and embryo transfer (IVF/ICSI-ET). Methods:This retrospective cohort study collected clinical data from patients undergoing IVF/ICSI-ET at the Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University between December 2020 and March 2024. Patients were divided into no history of pregnancy loss group (named control group, n=1 027) and RPL group ( n=743) based on history of pregnancy loss. Peripheral blood Hcy levels were compared between the two groups. Multivariate logistic regression was performed to adjust for confounding factors and determine whether Hcy is an independent risk factor for RPL. RPL patients were divided into four subgroups based on Hcy quartiles, named Q1 subgroup (Hcy<7.03 μmol/L), Q2 subgroup (7.03 μmol/L≤Hcy<8.63 μmol/L), Q3 subgroup (8.63 μmol/L≤Hcy<10.44 μmol/L), and Q4 subgroup (Hcy≥10.44 μmol/L), to further analyze the impact of Hcy level on pregnancy outcomes after IVF/ICSI-ET in these patients. Results:1) Baseline characteristics between control and RPL groups: statistically significant differences were observed in female age, male age, female body mass index (BMI), duration of infertility, cause of infertility, and peripheral blood Hcy levels (all P<0.05). 2) After adjusting for female age, male age, female BMI, duration of infertility, and cause of infertility via multivariate logistic regression, elevated Hcy levels was identified as an independent risk factor for RPL (a OR=1.366, 95% CI: 1.298-1.438, P<0.001). 3) Baseline characteristics of the four RPL subgroups: antral follicle count (AFC) differed significantly among Q1, Q2, Q3 and Q4 subgroups [17.00 (11.00, 24.00), 15.00 (10.00, 24.00), 14.00 (7.00, 22.25), 15.50 (8.00, 22.00), P=0.043]. No statistically significant differences were observed in other baseline characteristics (all P>0.05). 4) Pregnancy outcomes across the four RPL subgroups: miscarriage rates in the Q1, Q2, Q3 and Q4 subgroups were 18.18% (18/99), 30.61% (30/98), 33.70% (31/92), and 35.96% (32/89), respectively, live birth rates were 44.26% (81/183), 36.17% (68/188), 32.80% (61/186), and 30.65% (57/186), respectively. Intergroup differences in miscarriage rate and live birth rate were statistically significant ( P=0.033, P=0.036). Specifically, miscarriage rate in the Q3 and Q4 subgroups, and live birth rate in the Q4 subgroup were significantly higher than those in the Q1 subgroup (all q<0.05). However, no significant differences were observed in clinical pregnancy rate or early miscarriage rate among the four groups (all P>0.05). After adjusting for confounding factors using multivariate logistic regression, taking the Q1 subgroup as the control, there were no statistically significant differences in the clinical pregnancy rate between the remaining groups and the Q1 subgroup (all P>0.05). The early miscarriage rate in the Q3 subgroup (a OR=2.184, 95% CI: 1.077-4.426, P=0.030) and the early miscarriage rate in the Q4 subgroup (a OR=2.290, 95% CI: 1.116-4.697, P=0.024) were significantly higher than those in the Q1 subgroup; the miscarriage rate in the Q3 subgroup (a OR=2.207, 95% CI: 1.125-4.330, P=0.021) and the miscarriage rate in the Q4 subgroup (a OR=2.377, 95% CI: 1.209-4.674, P=0.012) were significantly higher than those in the Q1 subgroup; the live birth rate in the Q3 subgroup (a OR=0.615, 95% CI: 0.401-0.944, P=0.026) and the live birth rate in the Q4 subgroup (a OR=0.560, 95% CI: 0.364-0.863, P=0.009) were significantly lower than those in the Q1 subgroup. Conclusion:Elevated Hcy is a high-risk factor for RPL in IVF/ICSI-ET patients and may adversely affect pregnancy outcomes.

Objective:To investigate the pregnancy outcomes in patients ≤35 years old with diminished ovarian reserve (DOR) undergoing intrauterine insemination (IUI).Methods:A retrospective cohort study was conducted by analyzing the clinical data of 6 229 IUI cycles performed in patients aged ≤35 years at the Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University between June 2016 and March 2024. Based on serum anti-Müllerian hormone (AMH) levels, the subjects were divided into two groups: patients with AMH <1.1 μg/L were classified as the DOR group (489 cycles), and patients with AMH ≥1.1 μg/L were classified as the normal ovarian reserve (NOR) group (5 740 cycles). Propensity score matching (PSM) was applied to control for confounding factors, after 1∶1 PSM matching, 486 cycles were included in each group. Clinical pregnancy rate, miscarriage rate, live birth rate, biochemical pregnancy rate, and ectopic pregnancy rate were compared between the two groups by generalized estimating equations.Results:The clinical pregnancy rate was 21.19% (103/486) in DOR group and 24.07% (117/486) in NOR group, with no statistically significant difference ( P=0.294). The live birth rate was 18.31% (89/486) in DOR group and 20.16% (98/486) in NOR group, also without significant difference ( P=0.469). Additionally, no significant differences were observed in miscarriage rate, biochemical pregnancy rate, or ectopic pregnancy rate between the two groups (all P>0.05). Conclusion:In patients aged ≤35 years with DOR, pregnancy outcomes from IUI are comparable to those in young patients with NOR.

Objective:To investigate the mediating role of serum β-human chorionic gonadotropin (hCG) levels on the relationship between embryo quality and pregnancy outcomes following single frozen-thawed blastocyst transfer 14 d post-transfer.Methods:This retrospective cohort study collected data from patients who underwent in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) frozen-thawed single blastocyst transfer at the Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University between August 2017 and June 2021. Patients were grouped according to embryo quality into good-quality blastocyst group ( n=3 191) and available blastocyst group ( n=2 027). Differences in serum β-hCG levels and pregnancy outcomes at 14 d post-transfer were compared between the two groups. Mediation analysis and receiver operating characteristic (ROC) analysis were used to explore the mediating effect of β-hCG levels on the relationship between embryo quality and pregnancy outcomes and to evaluate the differences in the incidence of placental-related diseases between the two groups. Results:The good-quality blastocyst group had significantly higher serum β-hCG levels [1 177.0 (1.8, 2 278.5) U/L], clinical pregnancy rate [65.62% (2 094/3 191)], and live birth rate [52.55% (1 667/3 191)] compared with the available blastocyst group [54.4 (0.1, 1 453.5) U/L, P<0.001; 46.13% (935/2 027), P<0.001; 34.19% (693/2 027), P<0.001]. The early miscarriage rate in the good-quality group [13.47% (282/2 094)] was lower than that in the available blastocyst group [19.14% (179/935), P<0.001]. Serum β-hCG levels at 14 d post-transfer showed significant mediating effects on clinical pregnancy rate ( r=-0.126), live birth rate ( r=-0.122), and early miscarriage rate ( r=0.028) in both groups (all P<0.001). The cut-off values for β-hCG to predict live birth in the available and good-quality blastocyst groups were 366.9 U/L and 485.5 U/L, with positive predictive values of 76.28% (672/881) and 82.84% (1 628/1 965), respectively, and negative predictive values of 98.15% (1 114/1 135) and 96.14% (1 170/1 217). The cut-off values for predicting clinical pregnancy were 118.8 U/L and 226.5 U/L, with positive predictive values of 95.43% (919/963) and 98.45% (2 037/2 069), and negative predictive values of 99.72% (1 050/1 053) and 94.89% (1 059/1 116). The cut-off values for predicting early miscarriage were 1 337.0 U/L and 1 162.6 U/L, with positive predictive values of 32.75% (130/397) and 30.18% (150/497), and negative predictive values of 90.89% (489/538) and 91.73% (1 465/1 597). No differences were found in the incidence of placental-related diseases between the two groups (all P>0.05). Conclusion:This study indicates that both embryo quality and serum β-hCG levels at 14 d post-transfer significantly affect pregnancy outcomes. β-hCG levels play an important mediating role between embryo quality and pregnancy outcomes. ROC analysis demonstrates the good predictive efficacy of serum β-hCG levels for pregnancy outcomes, providing scientific evidence for optimizing embryo selection.

Objective:To investigate the impact of day 3 embryo quality on pregnancy outcomes in frozen-thawed single blastocyst transfer cycles and analyze its value in embryo selection.Methods:A retrospective cohort study was conducted on clinical data from patients undergoing frozen-thawed single blastocyst transfer at the Reproductive Health Hospital of the Third Affiliated Hospital of Zhengzhou University from January 2020 to December 2023. A total of 4 691 cycles of high-quality day 3 embryo (H-D3) group and 2 598 cycles of low-quality day 3 embryo (L-D3) group in the same period were included. Multivariate logistic regression was used to analyze the effects of day 3 embryo quality on clinical pregnancy rate (CPR) and live birth rate (LBR). All the cycles were stratified according to developmental day and quality of blastocyst: 3 920 cycles of high-quality day 5 blastocysts (H-D5), 1 271 cycles of low-quality day 5 blastocysts (L-D5), 834 cycles of H-D6 group and 1 264 cycles of L-D6, the influence of day 3 embryo quality was subsequently analyzed under different conditions.Results:1) Significant differences were observed between H-D3 and L-D3 groups in female age [(31.79±4.42) years vs. (32.28±4.43) years, P<0.001], basal follicle-stimulating hormone levels [6.24 (5.32,7.35) U/L vs. 6.48 (5.42,7.62) U/L, P<0.001], proportion of primary infertility [35.86% (1 682/4 691) vs. 31.99% (831/2 598), P<0.001], proportion of ≥2 prior failed embryo transfer cycles [3.77% (177/4 691) vs. 5.93% (154/2 598), P<0.001], proportion of gonadotropin-releasing hormone agonist/antagonist controlled ovarian hyperstimulation protocol in fresh cycles [93.33% (4 378/4 691) vs. 89.80%(2 333/2 598), P<0.001], embryo cryopreservation duration [3.10 (2.23,7.27) months vs. 3.60 (2.30,15.40) months, P<0.001], proportion of day 5 blastocyst transfers [74.82% (3 510/4 691) vs. 64.70% (1 681/2 598), P<0.001] and proportion of high-quality blastocyst transfers [72.59% (3 405/4 691) vs. 51.92% (1 349/2 598), P<0.001]. No significant differences were found in body mass index, infertility duration, endometrial preparation program or endometrial thickness on transfer day (all P>0.05). 2) Multivariable logistic regression analysis demonstrated that the L-D3 group had significantly lower CPR ( OR=0.837, 95% CI: 0.754-0.929, P<0.001) and LBR ( OR=0.880, 95% CI: 0.794-0.974, P=0.014) compared with the H-D3 group. 3) In H-D5 and L-D5 cycles, L-D3 did not significantly affect CPR ( aOR=0.941, 95% CI: 0.805-1.101, P=0.449; aOR=0.910, 95% CI: 0.724-1.142, P=0.415) or LBR ( aOR=1.034, 95% CI: 0.893-1.196, P=0.657; aOR=0.917, 95% CI: 0.729-1.153, P=0.457). However, in D6-H and D6-L cycles, L-D3 significantly reduced CPR ( aOR=0.732, 95% CI: 0.542-0.987, P=0.041; aOR=0.648, 95% CI: 0.515-0.815, P<0.001) and LBR ( aOR=0.645, 95% CI: 0.479-0.869, P=0.004; aOR=0.670, 95% CI: 0.526-0.854, P=0.001). Conclusion:Day 3 embryo quality significantly impacts both CPR and LBR in frozen-thawed day 6 single blastocyst transfer cycles. This suggests that day 3 embryo quality retains clinical relevance as a selection criterion when prioritizing day 6 blastocysts for transfer.