Good laboratory practice for PGT-M: Turkish Society of Reproductive Medicine guidelines.

This guideline was prepared by the Turkish Society of Reproductive Medicine to define the conditions and requirements for an outsourced preimplantation genetic testing (PGT) programme in line with the experience and needs of practitioners. This guideline is intended to be a reference document for assisted reproductive technology centres, genetic diagnosis centres, non-governmental organizations working on reproductive health, legal experts, consultants working on laboratory accreditation, academicians specializing in ethical issues, and policy makers. The Consortium aims to provide recommendations addressing the challenges of genetic testing, especially PGT for monogenic diseases (PGT-M) due to the high rate of consanguineous marriage in Turkey. For this purpose, this summary document specifically includes challenges and recommendations regarding PGT-M practice, and aims to identify and aid in prevention of errors leading to misdiagnosis. The recommendations can be modified to fit other locations.

Should the trigger to oocyte retrieval interval be different in progestin-primed ovarian stimulation cycles?

RESEARCH QUESTION: Does the trigger to oocyte retrieval interval (TORI) affect oocyte maturation rates differently in progestin-primed ovarian stimulation (PPOS) and gonadotrophin-releasing hormone (GnRH) antagonist cycles? DESIGN: This was a retrospective cohort study. The interaction between the stimulation protocol and TORI was assessed in a linear mixed effects multivariable regression analysis with oocyte maturation rate as the dependent variable, and stimulation protocol (GnRH antagonist or PPOS), age (continuous), gonadotrophin type (FSH or human menopausal gonadotrophin), trigger (human chorionic gonadotrophin [HCG] or GnRH agonist), TORI (continuous) and days of stimulation (continuous) as the independent variables. Oocyte maturation rate was defined as number of metaphase II oocytes/number of cumulus-oocyte complexes retrieved. The maturation rate was calculated per cycle and treated as a continuous variable. RESULTS: A total of 473 GnRH antagonist and 205 PPOS cycles (121 conventional PPOS and 84 flexible PPOS) were analysed. The median (quartiles) female age was 36 (32-40) years. Of these cycles, 493 were triggered with HCG and 185 with a GnRH agonist. The TORI ranged between 33.6 and 39.1 h, with a median (quartiles) of 36.2 (36-36.4) hours. Maturation rates were similar between fixed PPOS, flexible PPOS and antagonist cycles (median 80%, 75% and 75%, respectively, P = 0.15). There was no significant interaction between the stimulation protocols and TORI for oocyte maturation. CONCLUSIONS: PPOS cycles do not seem to require a longer TORI than GnRH antagonist cycles.

Comparing performance between clinics of an embryo evaluation algorithm based on time-lapse images and machine learning.

PURPOSE: This article aims to assess how differences in maternal age distributions between IVF clinics affect the performance of an artificial intelligence model for embryo viability prediction and proposes a method to account for such differences. METHODS: Using retrospectively collected data from 4805 fresh and frozen single blastocyst transfers of embryos incubated for 5 to 6 days, the discriminative performance was assessed based on fetal heartbeat outcomes. The data was collected from 4 clinics, and the discrimination was measured in terms of the area under ROC curves (AUC) for each clinic. To account for the different age distributions between clinics, a method for age-standardizing the AUCs was developed in which the clinic-specific AUCs were standardized using weights for each embryo according to the relative frequency of the maternal age in the relevant clinic compared to the age distribution in a common reference population. RESULTS: There was substantial variation in the clinic-specific AUCs with estimates ranging from 0.58 to 0.69 before standardization. The age-standardization of the AUCs reduced the between-clinic variance by 16%. Most notably, three of the clinics had quite similar AUCs after standardization, while the last clinic had a markedly lower AUC both with and without standardization. CONCLUSION: The method of using age-standardization of the AUCs that is proposed in this article mitigates some of the variability between clinics. This enables a comparison of clinic-specific AUCs where the difference in age distributions is accounted for.

IVF characteristics and the molecular luteal features of random start IVF cycles are not different from conventional cycles in cancer patients.

STUDY QUESTION: Are the IVF parameters and the steroidogenic luteal characteristics of random-start IVF cycles different from conventional cycles in cancer patients? SUMMARY ANSWER: No; controlled ovarian stimulation cycles randomly started at late follicular phase (LFP) and luteal phase (LP) are totally comparable to those conventional IVF cycles started at early follicular phase (EFP) in terms of the expression of the enzymes involved in cholesterol utilization and steroid hormone biosynthesis pathways, gonadotropin receptor expression and, estradiol (E2) and progesterone (P4) production in addition to the similarities in ovarian response to gonadotropin stimulation, oocyte yield, fertilization rate and embryo development competency in cancer patients. WHAT IS KNOWN ALREADY: Random start ovarian stimulation protocols are commonly employed for oocyte and embryo freezing for fertility preservation in cancer patients with time constraints who do not have sufficient time to undergo ovarian stimulation initiated conventionally at EFP of the next cycle. No data is available regarding the molecular steroidogenic features of these cycles analyzed together with the clinical IVF characteristics in cancer patients. We aimed to address this question in this study to help understand how similar the random start cycles are to the conventional start ones. STUDY DESIGN, SIZE, DURATION: A clinical translational research study conducted in 62 cancer patients undergoing IVF for fertility preservation between the years 2017 and 2022. PARTICIPANTS/MATERIALS, SETTING, METHODS: Sixty-two patients who were diagnosed with different types of cancer and underwent ovarian stimulation for oocyte (n = 41) and embryo (n = 21) cryopreservation using GnRH antagonist protocol and human menopausal gonadotropins before receiving cancer treatment/surgery were enrolled in the study. For patients with breast cancer and endometrial cancer the aromatase inhibitor letrozole was used with gonadotropin stimulation. Ovarian stimulation was initiated conventionally at EFP in 22 patients and served as control while it was started at LFP in 20, and mid-LP in the other 20 patients. The luteinized granulosa cells (GCs) were recovered from follicular aspirates during oocyte retrieval procedure and used for the experiments separately for each individual patient. The expression of the enzymes involved in sex steroid biosynthesis (StAR, 3ß-HSD, Aromatase) and cholesterol synthesis (3-hydroxy 3-methylglutaryl Co-A reductase (HMG-Co-A reductase)), utilization (hormone sensitive lipase (HSL)), and storage (Acetyl-Coenzyme A acetyltransferase 1 (ACAT-1)), and gonadotropin receptor expression status were analyzed using immunoblotting and RT-PCR methods. Laser confocal immunofluorescence imaging was applied to analyze and compare the expression patterns of the steroidogenic enzymes and their relation with mitochondria. In vitro E2 and P4 production by the cells were compared among the groups. MAIN RESULTS AND THE ROLE OF CHANCE: Baseline demographic and IVF characteristics of the patients undergoing the conventional start and random start IVF cycles were similar. Duration of gonadotropin stimulation was significantly longer in LFP and LP start cycles in comparison to the conventional ones. Ovarian response to gonadotropin stimulation, mature and total oocyte yield, fertilization and Day 5 blastulation rates of the embryos were comparable between the conventional versus random start cycles. When the luteal GCs of these random start cycles were analyzed we could not find any gross differences between these cycles in terms of the viability index and gross light microscopic morphologic features. More detailed analysis of the molecular luteal characteristics of the cells using RT-PCR, immunoblotting methods revealed that the expression profiles of the gonadotropin receptors, and the enzymes involved in sex steroid biosynthesis and cholesterol synthesis/utilization, and the steroidogenic activity of the luteal GCs of the random start cycles are almost identical to those of the conventional start cycles. Confocal image analysis demonstrated similar patterns in the signal expression profiles of the steroidogenic enzymes and their co-localization within mitochondria. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Caution should be exercised when interpreting our data and counseling cancer patients seeking fertility preservation because it is still unclear if previous exposure to cancer drugs, different ovarian pathologies or infertility etiologies, previous ovarian surgery and/or any other underlying diseases that are concomitantly present with cancer may cause a difference between conventional and random start stimulation protocols in terms of IVF parameters, luteal function and reproductive outcome. Relatively low number of patients in each stimulation protocol and pooling of luteal GCs for each patient rather than individual analysis of each follicle and oocyte are additional limitations of our study. WIDER IMPLICATIONS OF THE FINDINGS: Our findings provide reassurance that random start protocol offers cancer patients an equally good prospect of fertility preservation as conventional IVF. STUDY FUNDING/COMPETING INTEREST(S): Funded by the School of Medicine, the Graduate School of Health Sciences of Koc University and Koç University Research Center for Translational Medicine (KUTTAM), equally funded by the Republic of Turkey Ministry of Development Research Infrastructure Support Program. All authors declare no conflict of interest. TRIAL REGISTRATION NUMBER: N/A.

Outcomes of a GnRH Agonist Trigger Following a GnRH Antagonist or Flexible Progestin-Primed Ovarian Stimulation Cycle.

A suggested explanation for the pituitary-suppressive effects of progestin-primed ovarian stimulation cycles (PPOS) is pituitary luteinizing hormone (LH) depletion with progestin exposure during the follicular phase. The GnRH agonist (GnRHa) trigger releases endogenous LH from the pituitary, and if the LH depletion theory is correct, the response to the agonist trigger would be dampened in PPOS cycles. In this study, we compared the performance of the GnRHa trigger after PPOS and GnRH antagonist ovarian stimulation cycles. All women who underwent ovarian stimulation with the GnRH antagonist or flexible PPOS (fPPOS) and received a GnRH agonist trigger were eligible for inclusion. Outcomes included number of metaphase-II (MII) oocytes retrieved per cycle, rates of empty follicle syndrome, maturation, fertilization, blastulation, and cumulative clinical pregnancy per stimulation cycle. During the screening period, there were 166 antagonists and 58 fPPOS cycles triggered with a GnRH agonist. Groups were matched for potential confounders using propensity score matching. Progestin-downregulated cycles had 19% high mature oocyte yield (median: 14 vs. 19 MII oocytes, P = 0.03). Cumulative ongoing pregnancy or live birth rates were estimated after matching for transferred embryo count, and rates were similar between GnRH antagonist and fPPOS group (57.0% vs. 62.1%, P = 0.68). However, the number of remaining blastocysts was higher in the fPPOS group (median: 5.0 vs. 6.0, P < 0.001). LH levels were higher in fPPOS cycles compared to GnRH antagonist cycles up to the trigger day (P < 0.001). After the GnRHa trigger, fPPOS cycles were associated with a steeper LH surge compared with antagonist cycles (P = 0.02). Higher endogenous gonadotropin levels through the stimulation period and an LH surge of higher magnitude following a GnRHa trigger suggest a milder pituitary suppression by fPPOS, which needs to be confirmed in larger samples. It appears that progestins do not deplete pituitary LH reserves and a GnRHa trigger is usable after PPOS in women with high ovarian reserve.

Effectiveness of the flexible progestin primed ovarian stimulation protocol compared to the flexible GnRH antagonist protocol in women with decreased ovarian reserve.

The aim of this retrospective cohort study was to compare the effectiveness of the new flexible progestin primed ovarian stimulation (fPPOS) protocol with the flexible gonadotropin-releasing-hormone antagonist (GnRH-ant) protocol in women with decreased ovarian reserve (DOR). Twenty-seven women who underwent fPPOS and 54 age-matched women who received GnRH-ant for pituitary suppression were included in the study. All women had DOR and underwent oocyte cryopreservation. Three-hundred IU/day FSH was started on cycle day 2-3 and 0.25 mg/day GnRH-ant or 10 mg/day medroxyprogesterone acetate was started when the leading follicle reached 14 mm or serum oestradiol level was ≥200 ng/mL. The median duration of stimulation, day of commencing pituitary suppression and duration of suppression were similar in both groups, with 8, 5, and 5 days, respectively. The median number of cumulus-oophorous complexes (4.0 vs 5.5), metaphase-two oocytes (3 vs 4), the total number of oocytes cryopreserved (3.0 vs 4.5), and oocyte maturation rates (0.67 vs 0.70) were similar between the fPPOS and GnRH-ant groups, respectively. There was one case of premature ovulation in the fPPOS group and none in the GnRH-ant group (p = 0.91). In conclusion, fPPOS may be used in women with DOR without compromising the number of oocytes retrieved and seems a viable alternative to the flexible GnRH-ant protocol.

Dual Trigger Compared with Human Chorionic Gonadotropin Alone and Effects on Clinical Outcome of Intracytoplasmic Sperm Injection.

BACKGROUND: This study compared outcomes of the standard 6000 IU human chorionic gonadotropin (hCG) trigger with a dual trigger comprised of 6000 IU hCG and 1 mg leuprolide acetate for final oocyte maturation in an intracytoplasmic sperm injection (ICSI) cycle. By convention, ICSI was performed in most cases at the clinic. MATERIALS AND METHODS: In this retrospective study, a total of 50 women were included in each arm. Participants were matched for age, indication and number of prior assisted reproduction technology (ART) cycles. Women at risk for ovarian hyperstimulation syndrome (OHSS) were excluded. A flexible gonadotropin releasing hormone (GnRH) antagonist protocol was used and final oocyte maturation was triggered when two leading follicles were >17 mm. Distribution of variables was evaluated visually with histograms. Continuous variables were defined by mean (standard deviation) or median (25th-75th percentile) depending on distribution characteristics. Categorical variables were defined by numbers and percentages. Continuous variables were compared between the groups with the t test or Mann-Whitney U test as appropriate. Categorical variables were compared by the chi-square test and its derivatives as appropriate. A two-sided P<0.05 indicated statistical significance. RESULTS: Both groups had similar antral follicle counts, median parity (0) and number of previous failed cycles (0). The median number of oocytes (8 vs. 7), metaphase-two oocytes (6 vs. 5.5), blastocysts (1 vs. 1), clinical pregnancy rates (CPR) (28% vs. 22%), ongoing pregnancy rates (OPR) (22% vs. 20%) and pregnancy rate per transfer (53.3% vs 53.8%) were similar between the dual trigger and hCG only groups, respectively. CONCLUSION: Dual trigger for oocyte maturation stimulation failed to improve the ICSI outcome.

Do live birth rate and obstetric outcomes vary between immediate and delayed embryo transfers following freeze-all cycles?

RESEARCH QUESTION: Do live birth rates (LBR), obstetric and perinatal outcomes vary between women who underwent frozen embryo transfer (ET) in the immediately subsequent menstrual cycle, and with those who underwent delayed frozen ET. DESIGN: Retrospective cohort study (n = 198) consisting of 119 women who underwent immediate transfer within 30 days of oocyte retrieval (OR) and 79 women who underwent delayed transfer which was performed after >30 days following OR. Either flexible antagonist or flexible progestin-primed ovarian stimulation protocols were started after a baseline ultrasonography on the second or third day of menstrual cycle. Only freeze all cycles were included in the study and all transfers were with hormonal endometrial preparation. Main outcome measures were LBR, birth weight, gestational day at birth and pregnancy complications. RESULTS: Peak estradiol level on trigger day (2746 vs 2081 pg/ml) and number of metaphase-two oocytes (13 vs 10) were significantly higher in the immediate transfer group. Clinical pregnancy rate per ET was similar between the groups (50.4% vs 44.3%). However, miscarriage rate per positive pregnancy was significantly higher (12.3% vs 31.1%) while LBR per ET was significantly lower (42.9% vs 26.6%) in the delayed transfer group. Median gestational age at delivery were 267.5 and 268 days in the immediate and delayed transfer groups. Median birthweight was significantly higher in the delayed transfer group (3520 vs 3195 g). Adjusted analyses also suggest similar LBR with immediate and delayed transfer. CONCLUSION(S): Frozen ET in the immediate menstrual cycle and delayed ET, after a freeze all strategy did not show significant difference in terms of LBR after adjustment. Obstetric and perinatal outcomes of frozen ET in the immediate menstrual cycle appear reassuring.

Endometrial thickness is not predictive for live birth after embryo transfer, even without a cutoff.

OBJECTIVE: To investigate the predictive value of endometrial thickness (EMT) for live birth when a lower threshold of EMT is not employed for embryo transfer (ET). DESIGN: Retrospective study SETTING: Academic assisted reproduction center PATIENT(S): All women who underwent fresh or frozen-thawed ET at the Koç University Hospital Assisted Reproduction Unit between October 2016 and August 2019 INTERVENTION(S): After ruling out endometrial pathology, blastocyst transfer was planned regardless of the EMT in the absence of increased serum progesterone level on the trigger day in fresh embryo transfer cycles or before commencing progesterone treatment in artificially prepared frozen-thawed ET cycles. MAIN OUTCOME MEASURE(S): The primary outcome was live birth. Live birth and miscarriage rates per ET were stratified according to fresh and frozen-thawed ET cycles for each millimeter of endometrial thickness. Receiver operator characteristic curve analyses were performed to evaluate the predictive value of EMT for live birth. RESULT(S): A total of 560 ET cycles, 273 fresh and 287 frozen-thawed, were included in the study. Relevant patient characteristics as well as EMTs were similar between women who achieved a live birth and those who did not after fresh or frozen-thawed ET. There was no linear association between EMT and live birth or miscarriage rates. Area under the curve values for EMT to predict live birth after fresh, frozen-thawed, and all ETs were 0.56, 0.47, and 0.52, respectively. CONCLUSION(S): Our results showed that the EMT was not predictive for live birth in either fresh or frozen-thawed ET cycles. Once intracavitary pathology and inadvertent progesterone exposure were excluded, women with thinner EMTs should not be denied their potential for live birth because it is comparable to that of those with thicker EMT.

The Comparison of Fixed and Flexible Progestin Primed Ovarian Stimulation on Mature Oocyte Yield in Women at Risk of Premature Ovarian Insufficiency.

While gonadotrophin releasing hormone (GnRH) antagonists have been the standard of pituitary suppression during ovarian stimulation for ART, progestin primed ovarian stimulation (PPOS) has emerged as an alternative. Progestins can be started simultaneously with gonadotrophins (fixed PPOS) or later in the cycle depending on follicle growth (flexible PPOS). However, the flexible and fixed PPOS regimens have not been directly compared as of yet. This was a retrospective cohort study including women with diminished ovarian reserve who underwent oocyte cryopreservation. All women underwent ovarian stimulation with a fixed 300 IU daily dose of FSH. The primary outcome was the number of MII oocyte retrieved per cycle. Secondary outcome measures included the incidence of premature LH surge (>10ng/mL) and number of follicles larger than 14mm on the day of maturation trigger. During the screening period 2 out of 97 cycles were cancelled before oocyte retrieval, one in each group yielding an overall cancelation rate of 2%. Among women who had oocyte retrieval, 65 underwent flexible and 30 fixed PPOS. At baseline women on fixed and flexible PPOS had similar age (mean difference: -2.17 years, 95% CI: -4.46 to 0.11) and serum AMH levels (mean difference: 0.10 ng/mL, 95% CI: -0.24 to 0.47). Slight imbalances between the groups were rectified with propensity score matching using age and AMH levels. The incidence of premature LH surge (RR: 1.47, 95% CI: 0.51 - 5.27, p = 0.50), follicle count larger than 14mm on hCG day (RR: 1.14, 95% CI: 0.93 - 1.42, p = 0.22), number of MII oocytes retrieved (RR: 0.95, 95% CI: 0.79 - 1.15, p = 0.61) were similar between flexible and fixed PPOS. The rate of no oocyte retrieval was same between the groups (0.0% both) but no formal estimation was possible. Flexible and fixed PPOS regimens had no appreciable differences regarding MII oocyte yield and the incidence of premature LH surges. Cycles without oocyte retrieval were rare in both groups and ultrasonographic parameters of gonadotropin response were similar. Our study suggests the performances of either progestin regimen are comparable in this group of women.

Subcutaneous versus vaginal progesterone for vitrified-warmed blastocyst transfer in artificial cycles.

RESEARCH QUESTION: Does subcutaneous progesterone provide similar live birth or ongoing pregnancy rates as vaginal progesterone in frozen embryo transfer (FET) cycles? DESIGN: Retrospective cohort study (n = 214 women), consisting of 107 women who received subcutaneous progesterone for FET in artificial cycles and 107 women receiving vaginal progesterone who were matched for age and treatment cycle rank acted as controls. All embryos were transferred in an artificial cycle with 6 mg per day oral oestradiol valerate starting on the second or third day of the menstrual cycle. Patients underwent transvaginal ultrasound on the 10th day of priming, and subcutaneous progesterone (50 mg/day) or vaginal progesterone (180 mg/day) was started if the endometrium had a trilinear pattern regardless of its thickness. Embryo transfer was carried out on the sixth day of progesterone administration. Oestradiol and progesterone were continued until a negative pregnancy test, 10 days after the transfer, or until the completion of 10th gestational week. Main outcome measures were live birth or ongoing pregnancy rates. RESULTS: Baseline characteristics were similar between the groups. Positive pregnancy test rates (64.5% versus 58.9%; P = 0.40; RR 1.1; 95% CI 0.89 to 1.35), live birth or ongoing pregnancy rates (39.3% versus 35.5%; P = 0.57; RR 1.11; 95% CI 0.78 to 1.56) and miscarriage rates (29% versus 25.5%; P = 0.68; RR 1.08; 95% CI 0.76 to 1.55) were similar in the subcutaneous progesterone and vaginal progesterone groups, respectively. CONCLUSIONS: Subcutaneous progesterone seems to be an effective alternative to vaginal progesterone in patients undergoing FET. Randomized controlled trials comparing it with different progesterone preparations, routes and protocols are needed to better define its role.

Luteal granulosa cells from natural cycles are more capable of maintaining their viability, steroidogenic activity and LH receptor expression than those of stimulated IVF cycles.

STUDY QUESTION: Are there any differences in the molecular characteristics of the luteal granulosa cells (GC) obtained from stimulated versus non-stimulated (natural) IVF cycles that may help explain the defective luteal phase in the former? SUMMARY ANSWER: Luteal GC of stimulated IVF cycles, particularly those of agonist-triggered antagonist cycles, are less viable ex vivo, express LH receptor and anti-apoptotic genes at lower levels, undergo apoptosis earlier and fail to maintain their estradiol (E2) and progesterone (P4) production in comparison to natural cycle GC. WHAT IS KNOWN ALREADY: Luteal function is defective in stimulated IVF cycles, which necessitates P4 and/or hCG administration (known as luteal phase support) in order to improve clinical pregnancy rates and prevent miscarriage. The luteal phase becomes shorter and menstruation begins earlier than a natural cycle if a pregnancy cannot be achieved, indicative of early demise of corpus luteum (premature luteolysis). Supra-physiological levels of steroids produced by multiple corpora luteae in the stimulated IVF cycles are believed to inhibit LH release directly via negative feedback actions on the hypothalamic-pituitary-ovarian axis resulting in low circulating levels of LH and a defective luteal phase. We hypothesized that some defects in the viability and steroidogenic activity of the luteal GC of the stimulated IVF cycles might contribute to this defective luteal phase in comparison to natural cycle GC. This issue has not been studied in human before. STUDY DESIGN, SIZE, DURATION: A comparative translational research study of ex vivo and in vitro models of luteal GC recovered from IVF patients undergoing natural versus stimulated IVF cycles was carried out. Luteinized GC were obtained from 154 IVF patients undergoing either natural (n = 22) or stimulated IVF cycles with recombinant FSH and GnRH agonist (long) (n = 44), or antagonist protocol triggered conventionally either with recombinant hCG (n = 46) or with a GnRH agonist (n = 42). GC were maintained in vitro for up to 6 days. PARTICIPANTS/MATERIALS, SETTING, METHODS: Cellular viability (YO-PRO-1 staining), the expression of the steroidogenic enzymes, pro-apoptotic genes [Bcl-2-associated death promoter (BAD), Bcl-2-associated X protein (BAX) and Caspase-3 (CASP3)], anti-apoptotic genes [RAC-alpha serine/threonine-protein kinase (AKT-1) and Bcl-2-like protein 2 (BCL2-L2)], LH receptor, vascular endothelial growth factor (VEGF) (using real-time quantitative PCR at mRNA level and western blot immunoprecipitation assay at protein level) and in vitro E2 and P4 production (electrochemiluminescence immunoassay) were compared in GC among the groups. MAIN RESULTS AND THE ROLE OF CHANCE: Natural cycle GC were significantly more viable ex vivo (88%) compared to their counterparts of the stimulated IVF cycles (66, 64 and 37% for agonist and antagonist cycles triggered with hCG and GnRH agonist respectively, P < 0.01). They were also more capable of maintaining their vitality in culture compared to their counterparts from the stimulated IVF cycles: at the end of the 6-day culture period, 74% of the cells were still viable whereas only 48, 43 and 22% of the cells from the agonist and antagonist cycles triggered with hCG and agonist respectively, were viable (P < 0.01). The mRNA expression of anti-apoptotic genes (AKT-1 and BCL2-L2) was significantly lower, while that of pro-apoptotic genes (BAD, BAX and CASP3) was significantly higher in the stimulated cycles, particularly in the agonist-triggered antagonist cycles, compared to natural cycle GC (P < 0.01 for long protocol and antagonist hCG trigger, P < 0.001 for agonist trigger). The expression of steroidogenic enzymes (stAR, SCC, 3ß-HSD and aromatase) and VEGF was significantly higher in the agonist and hCG-triggered antagonist cycles compared to natural cycle GC. Therefore, in vitro E2 and P4 production in cells from the stimulated IVF cycles was significantly higher than their counterparts obtained from the natural cycles in the first 2 days of culture. However, after Day 2, their viability and hormone production began to decline very rapidly with the most drastic decrease being observed in the agonist-triggered cycles. By contrast, natural cycle GC maintained their viability and produced E2 and P4 in increasing amounts in culture up to 6 days. In vitro P production and the mRNA and protein expression of LH receptor, VEGF and 3ß-HSD were most defective in the agonist-triggered antagonist cycles compared to natural and agonist and hCG-triggered antagonist cycles. In vitro hCG treatment of a subset of the cells from the agonist-triggered cycles improved their viability, increased E2 and P4 production in vitro and up-regulated the mRNA expression of anti-apoptotic gene BCL-L2 together with steroidogenic enzymes stAR, SCC, 3B-HSD, LH receptor and VEGF. LARGE SCALE DATA: Not applicable. LIMITATIONS, REASONS FOR CAUTION: The limitations include analysis of luteinized GC only might not reflect the in vivo mechanisms involved in survival and function of the whole corpus luteum; GC recovered during oocyte retrieval belong to a very early stage of the luteal phase and might not be representative; effects of ovulation triggered with hCG may not equate to the endogenous LH trigger; the clinical characteristics of the patients may vary among the different groups and it was not possible to correlate stimulation-related molecular alterations in luteal GC with the clinical outcome, as no oocytes have been utilized yet. Therefore, our findings do not conclusively rule out the possibility that some other mechanisms in vivo may also account for defective luteal function observed in stimulated IVF cycles. WIDER IMPLICATIONS OF THE FINDINGS: Ovarian stimulation is associated with significant alterations in the viability and steroidogenic activity of luteal GC depending on the stimulation protocol and mode of ovulation trigger. Reduced survival and down-regulated expression of 3B-HSD, LH receptor and VEGF leading to compromised steroid production in stimulated cycles, and particularly in the agonist-triggered cycles, may at least in part help explain why the luteal phase is defective and requires exogenous support in these cycles. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the School of Medicine, the Graduate School of Health Sciences of Koc University and Koç University Research Center for Translational Medicine (KUTTAM), equally funded by the Republic of Turkey Ministry of Development Research Infrastructure Support Program. All authors declare no conflict of interest.