O-314 Investigating the embryonic contribution to recurrent pregnancy loss: a retrospective analysis of embryo quality, chromosomal status and morphokinetics in 11,169 embryos
Authors: Miguel-Escalada I , Lledó B , Stoop D , Zamora M  J , Mataró D , Rodríguez A , Popovic M 
Published: July 2024

Abstract

Study question
What is the embryonic contribution, in terms of embryo quality, chromosomal status and morphokinetics, to the reproductive success of recurrent pregnancy loss (RPL) patients?

Summary answer
RPL patients undergoing PGT-A had significantly fewer embryos available for biopsy, higher aneuploidy rates and showed morphokinetic alterations around the time of blastulation.

What is known already
RPL is diagnosed following the loss of two or more pregnancies before the 24th week of gestation. RPL has a multifactorial etiology encompassing both maternal and embryonic factors, such as uterine malformations, the presence of anti-phospholipid antibodies, maternal obesity or embryo aneuploidy, among others. While some studies have shown increased rates of chromosomal abnormalities in blastocysts from idiopathic RPL patients, a comprehensive characterization of the embryonic contribution to the disorder remains limited, and the role of embryo morphokinetics is still underexplored.

Study design, size, duration
This retrospective cohort study analyzed 11,169 embryos from 3,005 PGT-A cycles performed across 9 European fertility clinics between January 2017 and July 2023. Differences in the number of biopsied embryos, aneuploidy rates and embryo quality were compared between RPL and non-RPL patients. Morphokinetic timings were evaluated in a subset of 704 RPL embryos from 2 fertility centers, which was then compared to a separate cohort of embryos (n = 952) derived from double gamete donation cycles (n = 134).

Participants/materials, setting, methods
Genetic and clinical outcomes were assessed by multivariate analyses adjusting for maternal age, paternal age, the presence of male factor and embryo grade, as appropriate. Kaplan-Meier survival curves were constructed for each morphokinetic parameter (tPNf, t2, t3, t4, t5, t8, tSB and tB) and analyzed by Cox regression using maternal age and male factor as adjusting variables. P-values &lt;0.05 were considered statistically significant.

Main results and the role of chance
RPL patients undergoing PGT-A represented 15.47% (n = 465/3,005) of the cohort and were significantly younger than the rest of the patients (34,97±6.6 vs 36.38±6.6, p &lt; 0.0001). RPL patients obtained significantly fewer blastocysts available for biopsy (coefficient -0.39, 95%CI: -0.703- -0.076, p = 0.01) and had significantly higher aneuploidy rates (OR = 1.19, 95%CI: 1.06-1.35, p = 0.004). However, embryo quality (excellent vs. rest, p &gt; 0.05) was comparable between the two groups (n = 11,169 embryos). As anticipated, biochemical and clinical pregnancy rates were comparable between RPL patients and non-RPL patients (OR = 0.94, 95%CI:0.72-1.24, p = 0.68; OR = 0.95, 95%CI: 0.72-1.24, p = 0.71, respectively), however patients with RPL presented with significantly higher miscarriage rates (OR = 1.66, 95% CI:1.03-2.74, p = 0.04).
Compared to double donation embryos, RPL embryos exhibited significant delays in all analyzed times (tPNf: 23.7±3.1 vs. 22.7±3.1; t2: 26.5±4.1 vs. 25.6±3.4; t3: 37.1±5.4 vs. 36.0±4.7; t4: 39.2±6.3 vs. 37.9±5.3; t5: 50.2±7.9 vs. 49.3±7.4; tsB: 99.4±10.3 vs. 97.9±9.7; tB: 110.3±11.5 vs. 106.4±11.8; p &lt; 0.05). Notably, delays in blastocyst formation were also observed when adjusting for maternal age and male factor (Hazard Ratio=0.38, 95% CI: 0.18-0.79, p = 0.009). Significantly, morphokinetic alterations persisted even when exclusively comparing euploid RPL embryos to the double donation group (n = 41, t8: Hazard Ratio=1.78, 95% CI: 1.22-2.57, p = 0.002; tsB: Hazard Ratio=1.70, 95% CI: 1.17-2.48, p = 0.006).

Limitations, reasons for caution
The main limitation of the study is its retrospective design, where known RPL risk factors leading to the selection of a PGT-A cycle were not considered, potentially introducing biases.

Wider implications of the findings
These findings highlight the intricate interplay between embryo quality, aneuploidy, and morphokinetics in RPL, guiding personalized patient management. Higher embryo aneuploidy and morphokinetic alterations observed even in euploid RPL embryos suggest an embryonic role, underscoring the condition’s multifactorial nature and urging exploration of molecular mechanisms linking embryonic factors to RPL.

Trial registration number
not applicable