Exploring the efficacy and beneficial population of preimplantation genetic testing for aneuploidy start from the oocyte retrieval cycle: a real-world study

Embryo aneuploidy is the most common genetic abnormality in human blastocysts and is considered an important cause of low success rates during in vitro fertilization (IVF) [1]. Preimplantation genetic testing for aneuploidy (PGT-A) is used to identify euploid embryos prior to transfer to the uterus during IVF procedures. The first generation of PGT-A using fluorescence in situ hybridization was abandoned due to lack of efficacy [2, 3]. PGT-A based on comprehensive chromosomal screening is now widely used worldwide [4‐6]. However, its effectiveness remains unclear [4, 7‐13].

PGT-A is expensive; thus, identifying the patient population that would most benefit from this technique is imperative. According to the European Society of Human Reproduction and Embryology guidelines [14], the indications for PGT-A include advanced maternal age (AMA), recurrent pregnancy loss (RPL), recurrent implantation failure (RIF), and couples with severe male factor infertility. A multicenter, randomized control trial (RCT) revealed that a significant increase in ongoing pregnancy rate per embryo transfer was associated with PGT-A use in women aged 35–40 years with at least two embryos amenable to biopsy [9]. Another multicenter RCT confirmed that PGT-A neither increased live birth rates nor decreased miscarriage rates in patients with RPL and RIF [15]. However, several retrospective studies have suggested benefits of PGT-A, such as greater live birth rate (LBR) among women aged ≥ 35 years [16] and couples with RPL undergoing frozen-embryo transfer [17]. These conflicting results may be due to underlying selection bias toward good prognosis and normal ovarian reserve patients, while poor ovarian responders were still in question [9, 16, 18, 19]. Clinical outcomes were assessed based on transfer/detection cycles rather than oocyte retrieval cycles [9, 16], thereby not accounting for the effects of cycles without oocytes, absence of blastocysts for biopsy, or lack of euploid embryo for transfer on success rates. Moreover, some studies did not report cumulative success rates over time [9].

Therefore, in this retrospective cohort study, we compared single and cumulative transfer outcomes of first oocyte retrieval cycles in women with infertility with and without PGT-A after propensity score matching (PSM) to balance the clinical baseline. In addition, we examined the benefits derived from PGT-A across different age groups, body mass index (BMI), ovarian reserve/response, and potential indications via subgroup analyses.

Following the pre-designed inclusions and exclusions, 60,580 patients were included in the PSM for the overall cohort (Fig. 1), of which 4,409 (7.3%) underwent PGT-A. After 1:3 nearest-neighbor PSM matching, 4195 (95.1%) PGT-A users’ first oocyte retrieval cycles were matched to 10,140 oocyte retrieval cycles of non-users. Thus, the matching process resulted in a good balance for all covariates (SMD < 0.2) (Table 1 and Additional file 1: Figure S1).

After balancing baseline characteristics using PSM, we observed that PGT-A does not increase CLBR. Women aged ≥ 38 years, diagnosed with RPL or intrauterine adhesions benefit more from PGT-A, reflected in significantly higher CPR and LBR following the first transfer, without reduced CLBR. Furthermore, the single blastocyst transfer in the PGT-A group reduced the complications associated with multiple gestations.

CLBR effectively evaluates PGT-A’s effectiveness, as it can comprehensively reflect the final treatment outcome of an oocyte retrieval cycle [32]. Our overall analysis, including all embryo transfers occurring ≥ 12 months after initial oocyte retrieval, suggested that PGT-A did not improve CLBR after balancing the clinical baseline. This finding was consistent with those of previous studies [15, 18], reflecting some PGT-A limitations. Studies had confirmed that some mosaic embryos might progress to healthy live births [33], and chromosomal mosaicism was a critical factor causing embryo wastage and reduced CLBR [34, 35]. The incidence of mosaic embryos in this study was 6.7% (603/8996), within the reported 2–13% range [36]. Actually, safety concerns had limited the transfer of mosaic embryos to only 50 patients, which had resulted in 19 successful live births. Of the 3040 PGT-A patients who did not achieve live births, 228 patients still had 271 mosaic embryos that were not selected for transfer. The majority of these patients opted for a new PGT-A cycle instead. Taking into account the potential for healthy deliveries from mosaic embryos, it is reasonable to estimate that CLBRs would increase to approximately 29.2–30.1% if all mosaic embryos were transferred [34, 35, 37]. Moreover, embryonic mosaicism also affected the accuracy of embryo biopsy for PGT-A, and trophectoderm results might not always represent whole-embryo genetic composition [38, 39]. For example, when segmental aneuploidy was identified using PGT-A, studies suggested that > 50% of segmental aneuploidies were derived from mitosis errors [21, 40]. Besides, the invasive biopsy during PGT-A might reduce embryo implantation potential [41, 42].

A healthy singleton live birth is the target outcome for all infertility treatments. However, multiple gestation is the most common complication of assisted reproductive treatment [43]. Multiple gestations were at significant risk for prematurity [44], hypertensive disorders [45], and neonatal and fetal demise [46]. PGT-A significantly reduced the ratio of preterm birth and low birth weight. These results were similar to those of previous studies [47].

AMA is an important indication for PGT-A as it increases the risk of meiotic chromosome segregation errors [7]. Various countries and reproductive centers define the AMA threshold differently, with most lying between 35 and 38 years of age. Age-stratified subgroup analysis suggested that women aged ≥ 38 years might benefit more from PGT-A treatment than those aged > 35 years. PGT-A use could decrease CLBR in women aged 35–37 years; however, CLBR did not differ significantly between groups in the ≥ 38 years age strata. This finding provides clinical evidence supporting PGT-A use in women aged ≥ 38 years.

Aneuploidy causes most early pregnancy losses; therefore, RPL is a suggested indication for PGT-A [17, 48]. However, little high-quality evidence supports PGT-A use in women with RPL [8]. Our results demonstrated significantly increased LBR and a non-significant decrease in early miscarriage rate in the first transfer cycle with PGT-A use in women with RPL. However, the CLBR exhibited no significant inter-group difference. In addition, high PGT-A usage among women < 35 years of age was due to RPL in our data. Therefore, we further stratified the analysis among these patients according to RPL diagnoses and observed that in young women with RPL, PGT-A omission improved LBR in the first transfer cycle and achieved higher CLBR (without significance). Our findings should encourage clinicians to discuss PGT-A use in patients with RPL.

Finally, our results revealed that severe male infertility factors may not be an appropriate indication for PGT-A. Poor sperm quality may be associated with lower fertilization rate and embryo development potential but not with the euploidy rate [49, 50]. Origin analysis of whole chromosome aneuploidies in blastomeres and blastocysts suggested that 80–90% of chromosome aneuploidies affect maternally-derived chromosomes [51, 52]. Several retrospective analyses indicated a significantly higher rate of mosaic blastocysts in the male/severe male factor infertility groups than in the non-male factor infertility group [53‐55]. However, the majority of mosaic embryos were not transferred to the uterus. These may potentially explain why patients with severe male infertility factors derived minimal benefits from aneuploidy screening. Instead, they experienced embryo wastage as a result of PGT-A, leading to a significant reduction in CLBR.

Future studies are required to increase the extent of PGT-A embryo utilization, particularly in improving the accuracy of diagnosing mosaicism and elucidating the clinical significance of chromosome mosaicism, which will improve embryo selection and clinical management.

This retrospective analysis had several advantages over previous studies. First, using the complete data chain, we considered the full impact of oocyte retrieval or blastocyst formation on the comparison, starting with the patients’ wishes at the start of the cycle. Second, we analyzed CLBR based on the oocyte retrieval cycle rather than the transfer/detection cycle. Third, we used real-world data to reduce the selection bias caused by inappropriate inclusion. Nonetheless, this study has certain limitations. First, its retrospective design introduces inevitable bias. Second, some transferable embryos were not transferred in cycles that did not achieve live birth, especially in PGT-A cycles, of which 10.1% retained euploid embryos. We included the rate of these cycles in the two-group comparison; however, it could not fully reflect the true LBR. Third, these data were derived from a single IVF center; therefore, our results’ generalizability may be limited. Thus, multicenter studies with large data volumes are required to further confirm these findings.

Regardless of the mechanism responsible, this large real-world database study verified that PGT-A does not increase and might even decrease CLBR per oocyte retrieval cycle. However, PGT-A is undeniably effective in patients with specific indications. Careful selection of suitable populations and appropriate clinical management of mosaic embryos are important for effective PGT-A implementation.