Cumulative live births and predictive factors of emergency oocyte cryopreservation: a retrospective cohort study.

This retrospective cohort study included 137 oocyte cryopreservation-thaw cycles from 136 patients, with one patient undergoing two cycles (Fig.  1 ). Fig. 1 Flowchart of study participants. IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection Flowchart of study participants. IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection The median age of women at the time of oocyte retrieval was 30.0 years (IQR, 26.5–34.0), with a median of 12.0 oocytes cryopreserved (IQR, 8.0–16.5) and a median cryopreservation duration of 15.1 weeks (IQR, 9.0–44.5). Indications for OC were categorized as follows: (i) absolute male factor infertility (86 cycles), defined as unsuccessful sperm retrieval via masturbation or TESA/micro-TESE due to confirmed male infertility; and (ii) relative male factor infertility ( n  = 59 cycles), referring to unexpected circumstances—such as febrile illness or the male partner’s inability to attend the clinic on the day of oocyte retrieval—that prevented sperm collection. Baseline cycle characteristics stratified by OC indication are summarized in Table  1 . Women in the absolute male factor group were significantly younger at the time of oocyte retrieval compared to those in the relative male factor group (median 28.0 vs. 34.0 years). Furthermore, the prevalence of diminished ovarian reserve (1.1% vs. 17.6%) and tubal factor infertility (2.3% vs. 33.3%) was notably lower in this group. Among male partners in the absolute male factor group, azoospermia was diagnosed in 79.0% of cases, and donor sperm was ultimately used in 86.0% of cycles. In contrast, female infertility factors were more frequently identified in the relative male factor group. Azoospermia and oligoasthenoteratozoospermia were present in 13.7% and 35.3% of these male partners, respectively, and in 82.3% of these cases, ejaculated sperm from the male partner was utilized. Table 1 Basic characteristics of the vitrification-thaw cycles by indication for oocyte cryopreservation Characteristics Absolute male factor Relative male factor P -value Cycles (n) 86 51 Female age (at oocyte retrieval) 28.00 (26.00-30.62) 34.00 (30.00–38.00) <0.001 BMI (kg/m 2 ) 21.50 (19.78–24.04) 21.10 (19.70–22.80) 0.406 Infertility type <0.001  Primary infertility 91.8% (79/86) 54.9% (28/51)  Secondary infertility 8.1% (7/86) 45.0% (23/51) Duration of infertility (y) 3.00 (2.00–5.00) 3.00 (1.00–6.00) 0.868 Prior pregnancies ≥ 1 7.0% (6/86) 41.2% (21/51) <0.001 Prior births ≥ 1 0 7.8% (4/51) 0.018 Male infertility factors  Azoospermia 79.0% (68/86) 13.7% (7/51) <0.001  Oligoasthenoteratozoospermia 5.8% (5/86) 35.3% (18/51) <0.001 Female infertility factors  Endometriosis 0 5.8% (3/51) 0.050  PCOS 11.6% (10/86) 17.6% (9/51) 0.324  DOR 1.1% (1/86) 17.6% (9/51) <0.001  Tubal factor 2.3% (2/86) 33.3% (17/51) <0.001 Basal Hormones  FSH (mIU/mL) 5.69 (3.16-7.00) 6.29 (4.51–7.31) 0.194  LH (mIU/mL) 3.72 (1.36–5.39) 3.37 (2.07–5.19) 0.723  E2 (pmol/L) 136.50 (102.00-163.50) 152.00 (121.00-208.00) 0.016 Ovulation stimulation protocols 0.039  Antagonist 44.1% (38/86) 66.6% (34/51)  Long protocol 44.1% (38/86) 23.5% (12/51)  Prolonged protocol 10.4% (9/86) 7.8% (4/51)  Short agonist protocol 1.1% (1/86) 1.9% (1/51) Male age (at oocyte fertilization) 31.00 (28.00–34.00) 36.00 (32.00–40.00) <0.001 Eventual source of sperm <0.001  Husband masturbation 4.7% (4/86) 82.3% (42/51)  Husband surgical sperm extraction 9.3% (8/86) 17.6% (9/51)  Donor 86.0% (74/86) 0 Cryopreserved time (w) 23.71 (10.64–57.57) 11.71 (8.71–18.14) <0.001 BMI, body mass index; PCOS, polycystic ovary syndrome; DOR, diminished ovarian reserve; FSH, follicle stimulating hormone; LH, luteinizing hormone; E2, Estradiol Basic characteristics of the vitrification-thaw cycles by indication for oocyte cryopreservation BMI, body mass index; PCOS, polycystic ovary syndrome; DOR, diminished ovarian reserve; FSH, follicle stimulating hormone; LH, luteinizing hormone; E2, Estradiol A total of 1,740 oocytes were thawed. The median oocyte survival rate was 84.2% (IQR, 69.2-100.0%), with one cycle yielding no surviving oocytes. The median fertilization rate was 57.7% (IQR, 42.3-75.0%), and the median high-quality Day-3 embryo rate was 33.3% (IQR, 8.1-58.6%). Cycles with no transferable embryos accounted for 15.3% (21/137) of the total. Among the 107 cycles that underwent fresh ET, 33 cycles resulted in live births. For patients who had undergone embryo freeze-all cycles (for preimplantation genetic diagnosis or successive embryo accumulation) or did not achieve a live birth in a fresh ET cycle, 26 underwent frozen ETs further (21 patients had one frozen ET, and 5 patients had two frozen ETs), resulting in 7 live births. In 73.9% of ET cycles (102/138), two Day-3 embryos were transferred. Transfers involving Day-5/6 embryos and single embryo transfers accounted for 18.8% (26/138) and 23.9% (33/138) of cycles, respectively. As of December 2023, the CLBR for the entire cohort was 29.2% (40/137), with 7 patients who had not yet achieved a live birth still having frozen embryos. A detailed analysis of the embryological and reproductive outcomes associated with emergency oocyte vitrification cycles was subsequently conducted, with results summarized in Table  2 . In cycles with unsuccessful sperm retrieval, a significantly higher number of oocytes was retrieved (median 14 vs. 9), along with a greater number of 2PN fertilized oocytes (median 6 vs. 3), compared to cycles with relative male factor infertility. However, there were no significant differences between the two groups in terms of survival and fertilization rates. Additionally, cycles involving absolute male factor infertility yielded a higher number of high-quality Day-3 embryos (median 3 vs. 1) and a lower proportion of cycles with no usable embryos (6.9% vs. 31.4%) compared to those with relative male factor infertility. During the embryo transfer process, this group also demonstrated a higher implantation rate per embryo transferred (26.7% vs. 14.3%). Collectively, these advantages contributed to a significantly higher CLBR for cycles in the absolute male factor group compared to those in relative male factor group (39.5% vs. 11.8%). Among the 40 cumulative live births, no significant differences were observed in obstetric outcomes between the two groups. Table 2 Embryological and reproductive outcomes of the cryopreservation-thaw cycles by indication for oocyte cryopreservation Characteristics Absolute male factor Relative male factor P -value Number of mature oocytes retrieved 14.00 (10.75–18.25) 9.00 (6.00–12.00) <0.001 Oocyte survival rate 98.2% (78.6-100.0%) 94.7% (69.2-100.0%) 0.348 Inseminated oocytes (metaphase II) 11.00 (8.00–16.00) 7.00 (4.00–10.00) <0.001 Fertilized oocytes (two pronuclei) 6.00 (4.00–9.00) 3.00 (2.00–5.00) <0.001 Fertilization rate 60.0% (44.3-75.0%) 53.1% (41.3-78.3%) 0.716 High-quality Day-3 embryos 3.00 (1.00–5.00) 1.00 (0.00-2.25) <0.001 High-quality Day-3 embryo rate 45.0% (20.0-75.0%) 33.3% (0.0-60.0%) 0.070 Cycles without available embryo 6.9% (6/86) 31.4% (16/51) <0.001 Embryo transfer type 0.070 Fresh 73.8% (76/103) 88.6% (31/35) Frozen-thawed 26.2% (27/103) 11.4% (4/35) Embryo transfer day 0.072  3 77.7% (80/103) 91.4% (32/35)  5–6 22.3% (23/103) 8.6% (3/35) Number of transferred embryos 0.530  1 25.2% (26/103) 20.0% (7/35)  2 74.8% (77/103) 80.0% (28/35) Biochemical pregnancy per transfer cycle 43.7% (45/103) 25.7% (9/35) 0.060 Implantation per embryo transferred 26.7% (48/180) 14.3% (9/63) 0.046 Clinical pregnancy rate per transfer cycle 40.8% (42/103) 22.9% (8/35) 0.057 Miscarriage per clinical pregnancy 19.0% (8/42) 25.0% (2/8) 0.653 Cumulative live birth rate 39.5% (34/86) 11.8% (6/51) <0.001 Mode of delivery a 0.924  Vaginal 38.7% (12/31) 25.0% (1/4)  Caesarean delivery 61.3% (19/31) 75.0% (3/4) Gestational age (w) a 39.00 (38.00–40.00) 39.00 (38.00–40.00) 0.690 Birth weight (g) a 3300.00 (2825.00-3575.00) 3675.00 (3325.00-3800.00) 0.149 a Due to follow-up challenges, complete obstetric outcomes were collected for only a subset of the cycles. In the cohort of patients with absolute male factor, data on delivery mode were collected for 31 cycles, gestational age for 31 cycles, and birth weight for 29 cycles. In the cohort of patients with relative male factor, data on delivery mode were collected for 4 cycles, gestational age for 5 cycles, and birth weight for 4 cycles Embryological and reproductive outcomes of the cryopreservation-thaw cycles by indication for oocyte cryopreservation a Due to follow-up challenges, complete obstetric outcomes were collected for only a subset of the cycles. In the cohort of patients with absolute male factor, data on delivery mode were collected for 31 cycles, gestational age for 31 cycles, and birth weight for 29 cycles. In the cohort of patients with relative male factor, data on delivery mode were collected for 4 cycles, gestational age for 5 cycles, and birth weight for 4 cycles To further evaluate the clinical utility of emergency OC, patients with absolute and relative male factor infertility were matched to control cohorts undergoing ICSI using fresh oocytes. Matching criteria included female age at the time of fertilization, the presence of infertility factors in either partner, and eventual sperm origin. Comparative analyses of baseline characteristics and CLBR were conducted between each study group and its matched control cohort, with detailed results provided in Supplementary Tables 1 and CLBR visualized in Fig.  2 . In the absolute male factor infertility group, no statistically significant differences were observed in baseline characteristics or CLBR ( P  = 0.126) compared to the control group. Notably, the relative male factor infertility group exhibited a significantly lower number of mature oocytes retrieved ( P  = 0.025) and a reduced CLBR ( P  < 0.001) compared to its matched control. Fig. 2 Cumulative live birth rates by indication for oocyte cryopreservation: comparison between vitrification and control groups Cumulative live birth rates by indication for oocyte cryopreservation: comparison between vitrification and control groups The cumulative live birth rates are displayed on the Y-axis as percentages, accompanied by 95% confidence intervals. The corresponding table presents the cumulative live birth rate for each group, along with the absolute number of individuals who achieved a cumulative live birth and the total number of individuals within each group. Statistical comparisons between the vitrification and control groups were performed using the chi-square test. To explore the factors influencing the outcomes of emergency oocyte cryopreservation across various indications, we initially performed univariate regression analysis. However, due to the relatively small sample sizes in both groups, standard regression models did not identify any statistically significant factors affecting the cumulative live birth rate (Supplementary Tables 2 and 3 ). Consequently, we reanalyzed the data using bootstrap resampling methodology (Supplementary Tables 4 and 5 ). In cases of absolute male factor infertility, advanced female age at oocyte retrieval ( P  = 0.004) and prolonged infertility duration ( P  < 0.001) were negatively associated with the cumulative live birth rate. Additionally, sperm eventually obtained through husband surgical sperm extraction resulted in a significantly lower CLBR compared to donor sperm ( P  < 0.001). In cycles with relative male factor infertility, increased female age at oocyte retrieval also negatively affected the CLBR ( P  < 0.001). Additionally, the presence of male infertility factors ( P  < 0.001), a lower number of mature oocytes retrieved ( P  = 0.004), and prolonged oocytes cryopreservation duration ( P  = 0.008) were associated with decreased CLBR. Variables found significantly influenced outcomes in univariate analysis were subsequently included in multivariate bootstrap regression models for further analysis (Tables  3 and 4 ). Standard regression models are presented in the supplementary material (Supplementary Tables 6 and 7 ). In cases of absolute male infertility, the female partner’s duration of infertility (adjusted OR, 0.732; 95% CI, 0.652–0.821; P  < 0.001) and the use of surgically retrieved sperm from the male partner (compared to donor sperm; adjusted OR, 0.255; 95% CI, 0.093–0.698; P  = 0.008) were significantly associated with a reduced CLBR. For cycles involving relative male factor, older female age at oocyte retrieval (adjusted OR, 0.827; 95% CI, 0.740–0.923; P  < 0.001), number of mature oocytes retrieved (adjusted OR, 1.119; 95% CI, 1.024–1.222; P  = 0.013), and male infertility factors, including azoospermia or oligoasthenoteratozoospermia (adjusted OR, 0.086; 95% CI, 0.028–0.265; P  < 0.001), were independently associated with a decreased CLBR. Visual comparisons of cumulative live birth rates across different age groups and numbers of frozen-thawed oocytes, as shown in Fig.  3 , further supported these findings. In the group with absolute male factor infertility, the CLBR remained largely unaffected by the female partner’s age or the number of oocytes retrieved. In contrast, in the group with relative male factor infertility, the highest cumulative live birth rates were observed in younger women (< 35 years) and those who had a higher number of oocytes retrieved (≥ 10). Table 3 Multivariate bootstrap regression analysis of factors associated with cumulative live birth rate in cases of absolute male factor Characteristics Cumulative live birth rate, adjusted OR (95% CI) P -value Female age (oocyte retrieval day) 1.022 (0.959–1.088) 0.505 Duration of infertility (y) 0.732 (0.652–0.821) < 0.001 Eventual source of sperm  Husband masturbation 1.636 (0.636–4.209) 0.307  Husband surgical sperm extraction 0.255 (0.093–0.698) 0.008  Donor 1 Cryopreserved time (w) 1.000 (0.995–1.005) 0.982 Number of mature oocytes retrieved 1.022 (0.985–1.061) 0.247 OR, odds ratio; CI, confidence intervals Multivariate bootstrap regression analysis of factors associated with cumulative live birth rate in cases of absolute male factor OR, odds ratio; CI, confidence intervals Table 4 Multivariate bootstrap regression analysis of factors associated with cumulative live birth rate in cases of relative male factor Characteristics Cumulative live birth rate, adjusted OR (95% CI) P -value Female age (oocyte retrieval day) 0.827 (0.740–0.923) < 0.001 Male infertility factor 0.086 (0.028–0.265) < 0.001 Cryopreserved time (w) 0.993 (0.982–1.004) 0.491 Number of mature oocytes retrieved 1.119 (1.024–1.222) 0.013 OR, odds ratio; CI, confidence intervals Multivariate bootstrap regression analysis of factors associated with cumulative live birth rate in cases of relative male factor OR, odds ratio; CI, confidence intervals Fig. 3 Comparisons of cumulative live birth rate between different age and number of frozen-thawed oocytes groups. The cumulative live birth rates on the Y-axis are represented as percentages (the number of individuals in each group who achieved a cumulative live birth / the total number of individuals in the same group) Comparisons of cumulative live birth rate between different age and number of frozen-thawed oocytes groups. The cumulative live birth rates on the Y-axis are represented as percentages (the number of individuals in each group who achieved a cumulative live birth / the total number of individuals in the same group)

We conducted a retrospective, single-center cohort study involving women who underwent emergency OC and subsequent thaw cycles between January 1, 2017, and December 31, 2022. Indications for emergency OC included: (i) absolute male factor infertility ( n  = 86 cycles), defined as failed sperm retrieval by masturbation or testicular sperm aspiration (TESA)/microsurgical testicular sperm extraction (micro-TESE) due to confirmed male infertility; and (ii) relative male factor infertility ( n  = 59 cycles), encompassing unforeseen events—such as febrile illness or the male partner’s absence on the day of oocyte retrieval—that precluded sperm collection. Inclusion criteria required that each thaw cycle correspond to a distinct preceding freezing cycle. A total of 136 patients with complete demographic and clinical data were included, accounting for 137 thaw cycles, as one patient underwent two cryopreservation-thaw cycles. Propensity score matching (PSM) was employed to select an appropriate control group of patients who underwent intracytoplasmic sperm injection (ICSI) with fresh oocytes between January 1, 2017, and December 31, 2022. Matching criteria included female age at fertilization, the presence of infertility factors in either partner, and the source of sperm, to control for confounding variables and reduce selection bias. The study protocol was approved by the Ethics Committee of Peking University Third Hospital (Reg. No. 2018SZ-002). Ovarian Stimulation , Oocyte Retrieval , and Sperm Preparation All patients underwent ovarian stimulation in accordance with previously described protocols, with follicular development monitored via transvaginal ultrasound [ 30 ]. The ovarian stimulation protocols included the antagonist protocol, as well as the long, prolonged, and short agonist protocol. Final oocyte maturation was induced using 250 µg recombinant hCG (rHCG), 0.2 mg GnRH agonist (triptorelin), or a dual trigger, contingent upon at least two leading follicles reaching 18 mm. This decision was based on individual patient factors, including follicle count and estradiol levels. Oocyte retrieval was scheduled 36–38 h post-trigger. On the day of oocyte retrieval, to ensure the availability of sperm for fertilization, some semen samples were obtained through masturbation. For male partners diagnosed with severe oligospermia or non-obstructive azoospermia, TESA or micro-TESE was performed [ 31 ]. In instances where no sperm was detected in the semen samples or when the male partner was unable to provide a sample due to unforeseen circumstances, the retrieved MII-stage oocytes were subjected to vitrification. Oocyte vitrification and thaw Mature oocytes were preserved through vitrification using a Vitrification Kit (JIE YING Laboratory Inc., Canada) in accordance with the manufacturer’s protocol. Briefly, the oocytes were first equilibrated in a specific solution for 5 min at room temperature. They were then exposed to vitrification solutions for less than a minute at 25 °C and swiftly loaded onto sterile iVitri straws (catalog number RBC-S-008; Reprobiotech Corp., New Hyde Park, NY, USA). These straws were then promptly immersed in liquid nitrogen and stored at -190 °C. For thawing, a Thawing Kit (Jieying Laboratory Inc., Canada) was used according to the manufacturer’s guidelines. The oocytes were released from the straws into a 1.0 mol/L sucrose solution for 3 min, then sequentially transferred into 0.5, 0.25, and 0 mol/L sucrose solutions for 3 min each. Post-thaw, the oocytes were cultured in a medium containing human tubal fluid (catalog number LGGF-100; Life Global Group LLC, Guilford, CT, USA) at 37 °C in an atmosphere of humidified air with 5% CO2. After 2 h of incubation, the survival of the oocytes was evaluated based on membrane integrity and ooplasm discoloration. Preparation for insemination occurred 3 h after the incubation period [ 32 , 33 ]. Oocyte fertilization and embryo culture , cryopreservation , and transfer All metaphase II (MII) oocytes from the control group (fresh) and the OC group (thawed) were inseminated via ICSI. Fertilization was assessed 16–18 h post-ICSI, based on the presence of two pronuclei (2PN) and two polar bodies (PBs). Following insemination, embryos were cultured in G-M™ medium (LifeGlobal, CT, USA) supplemented with 10% synthetic serum substitute (SSS; Irvine Scientific, CA, USA). Embryo development and quality were assessed 64–66 h post-ICSI (Day 3), based on blastomere number and symmetry, degree of fragmentation, and cytoplasmic appearance. In most cycles producing high-quality Day-3 embryos, fresh embryo transfer (ET) was performed immediately, while the remaining embryos were either frozen at once or cultured to the blastocyst stage for subsequent cryopreservation. The cryopreservation of embryos was executed via vitrification, with thawing conducted as described previously [ 32 ]. ET, whether fresh or frozen, was timed according to the patient’s menstrual cycle and could occur during a natural, artificial, or stimulated cycle. The strategy for luteal support is the same as in the previous literature [ 30 ]. Outcomes Cryopreservation duration was defined as the interval between OC and subsequent oocyte warming. The oocyte survival rate was calculated as the proportion of oocytes that remained viable after warming relative to the total number of oocytes warmed. The fertilization rate was defined as the percentage of inseminated oocytes that developed into two-pronuclei (2PN) embryos. High-quality Day 3 embryos were defined as those containing 5 to 8 blastomeres, exhibiting less than 30% cytoplasmic fragmentation, and possessing uniformly sized blastomeres. A biochemical pregnancy was defined by a serum hCG level exceeding 10 IU/L, measured 14 days after ET. Clinical pregnancy was confirmed by the visualization of at least one gestational sac via ultrasound 30 days post-ET. The implantation rate was calculated as the number of gestational sacs observed divided by the number of embryos transferred. A miscarriage was defined as the spontaneous loss of pregnancy before 24 weeks of gestation. A live birth was defined as the delivery of at least one living infant following the transfer of fresh or vitrified/warmed embryos. Birth outcomes were assessed using parameters such as mean gestational age and birth weight. The primary outcome of this study was the cumulative live birth rate, defined as the achievement of at least one live birth within a single oocyte thaw cycle through the transfer of fresh or cryopreserved embryos, with all transfers completed before December 2023. Following the successful delivery of a live infant via ICSI, the woman was excluded from further cumulative live birth rate calculations within that cycle.

Emergency oocyte cryopreservation achieved a cumulative live birth rate of 29.2% per cryopreservation–thaw cycle, supporting its use in cases of unexpected sperm unavailability. Key factors associated with reduced live birth outcomes differed by the type of male factor infertility. In absolute male factor cases, prolonged infertility duration and use of surgically retrieved sperm were linked to poorer outcomes. In relative male factor cases, advanced maternal age, abnormal semen parameters, and a limited number of vitrified oocytes were significant risk factors. These findings highlight the need for individualized patient counseling to optimize outcomes in urgent fertility preservation settings.

In this retrospective cohort study, we evaluated the clinical efficacy of emergency OC and identified factors associated with reproductive outcomes by analyzing six consecutive years of clinical data from our center. The overall CLBR per cryopreservation-thaw cycle was 29.2%. Specifically, among cycles performed for absolute male factor infertility, the CLBR was higher, at 39.5%. However, prolonged infertility duration and the necessity for surgical sperm retrieval from the male partner were significant predictors associated with poorer reproductive outcomes. In contrast, cycles performed for relative male-factor infertility exhibited a substantially lower CLBR of 11.8%. In these cases, advanced maternal age at the time of oocyte retrieval, fewer mature oocytes retrieved, and a previous diagnosis of azoospermia or oligoasthenoteratozoospermia in the male partner emerged as significant negative prognostic factors. The study found that 62.8% of emergency OC cycles encountered sperm absence due to the male partner’s inability to produce sperm via masturbation or TESA/micro-TESE on the day of oocyte retrieval, mainly because of severe oligoasthenoteratozoospermia or non-obstructive azoospermia. The remaining 37.2% of patients experienced unexpected incidents that prevented timely sperm collection. Compared to a study conducted between March 2009 and October 2017 (unexpected partner absence, 11.0%; unavailable sperm from ejaculate or surgical extraction, 89.0%) [ 21 ], the incidence of partner absence increased, likely due to COVID-19 public health restrictions that impeded clinic visits. Among couples diagnosed with absolute male factor infertility—who constituted the majority of oocyte cryopreservation cases in our cohort—there was a consistent and marked preference for achieving fertilization using the male partner’s own sperm. In instances of failed sperm retrieval, oocyte vitrification served as an interim strategy that prevented the loss of mature oocytes while preserving the opportunity for future use of autologous sperm. Compared with immediate fertilization using donor sperm, this approach was more congruent with the couples’ expressed desire for a genetically related child. One illustrative case involved the only couple in the cohort who underwent two successive cycles of oocyte vitrification and warming. The male partner had been diagnosed with azoospermia on the basis of routine semen analysis and expressed strong opposition to the use of donor sperm. On the day of the initial oocyte retrieval, he underwent TESA, which failed to yield spermatozoa; the retrieved oocytes were thus vitrified. Following warming of this cohort, a second TESA procedure was performed, during which sperm were successfully retrieved and used for ICSI. Despite this, no viable embryos were obtained. A third TESA was attempted on the day of the second oocyte retrieval, which also proved unsuccessful, necessitating another cycle of oocyte vitrification. Following warming of the second cohort of oocytes, fertilization was performed using donor sperm, in accordance with the couple’s updated treatment decision. Cases of OC attributed to sperm retrieval failure were predominantly observed in younger women presenting with primary infertility, characterized by lower prevalence of diminished ovarian reserve and tubal infertility factors, thus underscoring severe male-factor infertility as the principal indication for OC. Consistent with this, donor sperm was utilized for fertilization in 81.3% of these cycles. Conversely, cycles initiated due to unexpected absence of the male partner were more frequently encountered among women of advanced reproductive age and were associated with higher incidences of female infertility factors, as well as a reduced number of mature oocytes retrieved. Collectively, these demographic and clinical characteristics elucidate important differences between patient groups, providing critical context for understanding subsequent clinical outcomes and identifying prognostic determinants of OC cycles. The study included both fresh and frozen ET cycles following OC, providing a comprehensive evaluation of embryological and reproductive outcomes in emergency oocyte vitrification. Assessed outcomes included survival rate, fertilization rate, biochemical pregnancy rate, implantation rate, clinical pregnancy rate, miscarriage rate, and CLBR. For the calculation of biochemical pregnancy rate, implantation rate, clinical pregnancy rate, and miscarriage rate, the outcomes of fresh and frozen embryo ETs were combined, as no significant differences were observed between fresh embryo transfer cycles and frozen embryo transfer cycles. Recent large-scale studies on autologous vitrified oocytes have reported survival rates ranging from 80 to 90% [ 23 , 25 – 27 , 37 , 38 ], consistent with our study’s survival rate of 84.2%. Although the median fertilization rate (57.7%), clinical pregnancy rate per transfer cycle (36.2%), and CLBR (29.2%) observed in our study are relatively lower than the outcomes reported in these previous studies, this discrepancy is justifiable, as those studies mainly involved oocyte vitrification for women aiming to avoid the gonadotoxic effects of cancer treatment or age-related fertility decline, rather than dealing with infertility problems in either partner. On the other hand, our final outcomes align closely with previous studies on emergency oocyte vitrification, such as those by Fu et al. and Zhan et al., who reported CLBR of 32.5% and 34.1%, respectively [ 22 , 39 ]. Differences in CLBRs reported in other studies on emergency oocyte vitrification may be due to smaller sample sizes [ 19 , 20 ] or the use of slow freezing techniques instead of vitrification [ 18 ]. To evaluate the clinical utility of emergency OC, we compared outcomes from vitrification cycles to those from a control cohort undergoing ICSI with fresh oocytes. Due to significant baseline differences between patients categorized as having absolute versus relative male factor infertility, separate control groups were matched for each subgroup to ensure appropriate comparisons. In the relative male factor group, CLBR was significantly lower in the cryopreservation cohort compared to controls. This disparity may be explained by the only significant baseline difference identified between the groups: the number of mature oocytes retrieved. A recent study by Zhan et al. supports this interpretation, reporting that patients undergoing cryopreservation following sperm retrieval failure due to acute, non-permanent events (e.g., stress-induced temporary anejaculation) had fewer oocytes retrieved and lower CLBR compared to those using fresh oocytes [ 39 ]. These findings suggest that individuals who opt for emergency OC in the context of relative male factor infertility may have diminished ovarian reserve, leading to fewer mature oocytes and, consequently, reduced reproductive potential. In this context, the poorer outcomes observed in the cryopreservation group may reflect underlying patient characteristics rather than the effect of vitrification itself. In the absolute male factor cohort, no significant difference in CLBR was observed between the vitrified and fresh oocyte groups, suggesting that the delay introduced by emergency OC did not adversely affect reproductive outcomes. Taken together, these findings suggest that emergency oocyte vitrification constitutes a clinically acceptable fallback strategy in situations where sperm is unavailable from the male partner on the day of oocyte retrieval. Although reproductive outcomes did not differ significantly between patients with absolute male factor infertility and a matched control group—adjusted for female age, infertility diagnosis in either partner, and final sperm source—the majority of patients in the absolute male factor cohort ultimately required the use of donor sperm. Given these findings, the routine use of emergency OC in this population warrants reconsideration, particularly in the absence of demonstrable improvements in cumulative live birth rates. These results underscore the importance of incorporating donor sperm as a planned contingency within OC strategies. Accordingly, the decision to pursue OC should be guided by individualized counseling that takes into account the couple’s reproductive goals, prognosis, and logistical considerations. Patients undergoing emergency OC have high expectations for treatment outcomes and are particularly concerned with the efficacy and influencing factors of their cycles. Hagege et al., in a discussion on fertility preservation consultation, emphasized the importance of identifying the optimal age and the ideal number of oocytes in OC cycles [ 12 ]. In the absolute male factor cohort, a longer duration of infertility emerged as a negative prognostic factor, consistent with prior literature [ 40 – 42 ]. Furthermore, cycles utilizing surgically retrieved sperm were associated with inferior clinical outcomes compared to those using ejaculated sperm. However, given the small number of cases in each subgroup (9.3%, 8/86), these findings should be interpreted with caution and warrant further validation in larger, adequately powered studies. In the relative male factor cohort, both maternal age at oocyte retrieval and the number of mature oocytes retrieved—two well-established predictors of assisted reproductive outcomes [ 22 , 23 , 26 , 27 , 29 , 37 , 38 , 43 – 46 ]—were significantly associated with CLBR. Compared with the absolute male factor group, women in this cohort were significantly older and had a lower mature oocyte yield. Notably, while these female-related factors significantly influenced CLBR in the relative male factor group, they did not exert a measurable effect in the absolute male factor group. These findings suggest that, in the relative male factor group, progressive maternal aging and further declines in oocyte yield—superimposed on an already advanced reproductive age and diminished ovarian response—may contribute significantly to the observed reduction in CLBR. Also, we found that the duration of OC did not significantly affect the CLBR of either group, which is consistent with several studies [ 22 , 23 , 47 , 48 ]. Our study has several strengths: First, the study includes both fresh and frozen embryo transfer cycles, allowing for the evaluation of CLBR—a clinically meaningful endpoint in assisted reproductive technology—and enabling more precise and individualized patient counseling. Second, to our knowledge, this is among the first studies on emergency oocyte vitrification to systematically investigate the factors associated with CLBR across distinct clinical indications for vitrification, through comprehensive subgroup analyses. Third, the analysis includes all consecutive cases of emergency oocyte vitrification and subsequent warming cycles conducted between 2017 and 2022 at one of the largest ART centers in China, using data extracted from electronic medical records to ensure accuracy and reduce recall bias. The study has several limitations: (1) The findings are derived from a single-center cohort, which may limit their generalizability to other populations. (2) The sample size is relatively small, necessitating further studies with larger cohorts to validate these conclusions. (3) This is a retrospective study, and conducting randomized controlled trials (RCTs) on emergency oocyte vitrification poses significant challenges. As a result, there may be a paucity of high-level evidence in this area.

All statistical analyses were conducted using SPSS version 27.0 (IBM Corp., Armonk, NY, USA). As individual couples could undergo multiple cycles of oocyte vitrification and thaw, analyses were conducted at the cycle level rather than the patient level. Cycles were categorized into two groups based on indications for emergency OC: absolute male factor group and relative male factor group. Cycles were categorized into two groups based on the indications for emergency OC: the absolute male factor group and the relative male factor group. Normality of continuous variables was assessed using the Kolmogorov-Smirnov test. For skewed data, results were presented as medians with interquartile ranges (IQRs). Group comparisons were performed using the Mann-Whitney U test. Categorical variables were expressed as frequencies and percentages, and differences between groups were assessed using the chi-square test or Fisher’s exact test, depending on the data distribution. To investigate potential factors associated with the outcomes of emergency OC across different clinical indications, we initially performed standard univariate and multivariable regression analyse. Given the relatively small sample sizes and the potential non-normal distribution of the outcome variables, bootstrap regression analysis was subsequently applied to improve the robustness of the estimates [ 34 – 36 ]. Specifically, 95% confidence intervals for regression coefficients (B) and odds ratios (OR) were calculated based on 3,000 times bootstrapped outputs. All statistical tests were two-tailed, with a P value of less than 0.05 considered statistically significant.

In 1986, Chen reported the first successful pregnancy and live birth from a vitrified human oocyte [ 1 ]. Over the past two decades, advancements in oocyte vitrification techniques, particularly cryopreservation, have significantly enhanced the survival, fertilization, cleavage, and pregnancy rates of vitrified oocytes [ 2 , 3 ]. Studies indicate that, for young women, the fertilization and pregnancy rates of cryopreserved oocytes are not statistically different from those of fresh oocytes [ 4 , 5 ]. Furthermore, there is no notable increase in chromosomal abnormalities or congenital anomalies among live births from cryopreserved oocytes [ 6 , 7 ], affirming the safety of this preservation method. In 2013, the American Society for Reproductive Medicine (ASRM) recommended that oocyte cryopreservation (OC) be considered a standard clinical practice rather than an experimental technique [ 8 ]. Consequently, OC has become a crucial technology for both medical and non-medical fertility preservation in women. Currently, autologous oocyte vitrification is primarily utilized for fertility preservation in patients with malignant tumors or autoimmune diseases prior to gonadotoxic treatment, for the accumulation of oocytes in poor responders, and to address age-related fertility decline [ 8 – 13 ]. Additionally, autologous OC is indicated in emergency situations where the male partner is unexpectedly unavailable to provide a sperm sample on the day of oocyte retrieval or in cases of sperm retrieval failure, and the patient opts not to use donor sperm. These emergencies include unexpected unavailability of the partner, absence of motile sperm in the ejaculated sample, or the inability to retrieve usable sperm through surgical sperm extraction [ 14 , 15 ]. In recent years, advances in male infertility treatments, particularly in microsurgical sperm retrieval techniques, have enabled patients previously reliant on donor sperm to achieve biological parenthood. However, these advancements have also led to an increase in cases where no sperm is obtained during concurrent microsurgical sperm retrieval on the day of oocyte retrieval [ 16 , 17 ]. Therefore, research on emergency OC due to male factors is crucial. Although emergency OC is not a newly emerging need resulting from socio-economic development, it remains a relatively rare and unpredictable scenario, unlike other indications that target specific populations. Consequently, studies focusing on emergency OC are limited compared to other indications for OC [ 18 – 22 ]. Most reports on autologous OC do not involve or rarely include patients undergoing emergency cryopreservation [ 23 – 29 ], making it challenging to extrapolate these outcomes to assisted reproductive technology (ART) results for patients primarily undergoing cryopreservation due to male factors. This gap in research is significant as it impacts the ability of healthcare providers to offer informed counseling and guidance to patients during decision-making processes. To assess the outcomes of emergency OC, we conducted a retrospective cohort study using six years of clinical practice data from the Reproductive Health Center of Peking University Third Hospital. The primary aim of this study was to evaluate the overall efficacy, measured by cumulative live birth rates (CLBR), and to identify predictive factors of emergency OC, which might help in providing clearer guidance for clinical practice.

Below is the link to the electronic supplementary material. Supplementary Material 1 Supplementary Material 1