Purpose: Selecting an embryo at the transfer stage with the best chance of a successful pregnancy is still largely dependent on preceding subjective evaluation of morphokinetics. Expensive prenatal genomic profiling has been so far proved ineffective. Proteomics and metabolomics are promising new approaches to assess embryo viability, but methodologies are often complex and do not lend themselves to rapid analysis in the critical time between blastocyst formation and embryo transfer. Here, we used matrix-assisted laser desorption ionization time-of-flight (MALDI ToF) mass spectrometry to assess the secretome of blastocysts in the minutes prior to embryo transfer and correlated spectral features with pregnancy outcome.
Methods: Four hundred one samples of spent blastocyst culture media were collected from embryo cultures at the time of embryo transfer, of which 136 were used to construct the predictive model. The media samples were frozen at - 20 °C and stored for analysis. Sample analysis was conducted in batches using 1 μl of spent embryo in direct MALDI ToF mass spectral analysis. Quantitative characteristics within this mass range (2000-17,000 m/z) were used to generate a score for selected mass regions (bins) in order to predict pregnancy outcome for each sample.
Results: With a simple algorithm based on nine mass bins within the 2000-10,000 m/z region, it was possible to identify samples with the best chance of becoming an ongoing pregnancy (positive predictive value of 82.9%, p = 0.0018).
Conclusion: A simple, direct and rapid analysis of spent culture fluid from blastocysts at the point of embryo transfer can quickly identify optimal embryos with the best chance of achieving ongoing pregnancy. Methods like this, which take less than 20 min to perform, could dramatically improve the approach to embryo selection and live births.
Keywords: Blastocyst; Culture media; Mass spectrometry; Non-invasive; Proteomics; Secretome.