Table 1. Studies addressing methods to evaluate mammalian embryos by non-invasive or invasive techniques.
Authors Technique Nature Species Embryo stage Compared
to what
traditional technique
On what
parameters
Pros Contras Sample
Size
Lindner & Wright, 1983 Morphological assessment by stereomicroscopy Non-
invasive
Bovine From morula
to hatched
blastocyst
Physiological parameters of development kinetics and pregnancy rates Embryo stage and quality (excellent, good, fair and poor) on pregnancy rates Embryo quality was a useful predictor of the pregnancy rate Subjectivity of the embryo quality assessment; excellent and good qualities had no difference on pregnancy rate 783
Gardner & Schoolcraft, 1999 Morphological assessment by stereomicroscopy Non-
invasive
Human Blastocyst Morphological aspects of the trophectoderm and inner cell mass Blastocyst quality based on grades Validated worldwide by embryologists and clinicians due its useful relation with pregnancy establishment Does not cover all aspects of the aberrant morphology and it is limited to blastocyst stage ND
Balaban et al., 2006 Morphological assessment by stereomicroscopy Non-
invasive
Human Blastocyst Comparison between the Gardner and Dokras systems of evaluation Clinical pregnancy, implantation rate and multiple pregnancies Both systems were practical and accurate, good to predict blastocysts with high implantation potential and to limit the number of embryo transfer to avoid multiple pregnancies Lack of a single and unified system and a standard to evaluate 132
Richardson et al., 2015 Simplified method to evaluate blastocysts Non-
invasive
Human Day 5
blastocyst
Traditional method to evaluate embryo morphology New and simplified method with less parameters to assess Faster and easier than the traditional method (Gardner & Schoolcraft, 1999) with similar or better results than a more complex system Method rarely used by clinicians 80
Shiku et al., 2001 Scanning electrochemical microscopy (SECM) Non-
invasive
Bovine From morula
to blastocyst
NA Results showed that morulae with higher oxygen consumption were faster to develop into blastocysts. The method could be just a complement or to change the way how the embryo is chosen Non-invasive technique that could be reliable to the embryo viability assessment and development Not well established and worldwide acceptation 19
Braga et al., 2015 Mass spectrometry to characterize (“fingerprint”) the culture medium conditioned by the embryo Non-
invasive
 
Human Day 3 of culture Spectroscopy To identify potential embryo lipid biomarkers that are predictors to preview blastocyst formation Promising approach to identify embryos that should be cultured until Day 5 or cryopreserved   50
Yang et al., 2012 Chromosomal screening by array Comparative Genomic Hybridization (aCGH) Invasive Human Day 5 NA Together with morphological evaluation presented the best results Produced clinical pregnancy more frequently and a lower abortion rate when compared to embryos chosen without a CGH Demands skills from the embryologist and complex equipment to perform the invasive technique 814
Kropp et al., 2014 Micro RNA (miRNA) profile Non-
invasive
Bovine and Human Day 5 or 6 NA Potential to develop non-invasive biomarkers to predict embryo quality Embryo quality related with some miRNA expression Needs more studies and development of robust and accurate biomarkers 216
(bovine embryos)
Kakourou et al., 2013 Transcriptomic analysis Invasive Human Blastocyst NA Results highlighted the importance of the hormones and their receptors but lack a physiologic comprehension of their role on the early development Future analyses could identify new biomarkers that predict embryo development potential Still an experimental method that needs more studies 03
Farin et al., 1995 Videotape assessment of embryo images Non-
invasive
Bovine From morula to blastocyst NA Way to measure inter-embryologist agreement. Quality Good to excellent agreement existed for classifying Day 7 embryos by stage and by extremes of quality grade (grades 1 and 4). It was proposed a simple grading criteia to maximize agreement among evaluators There was poor agreement of evaluators by degree of abnormal morphology
(Grades 2 and 3)
40
VerMilyea et al., 2014 Time-lapse Non-
invasive
Human Day 1 to 3 NA Strong prediction of the clinical pregnancy when related to P2 (time between 1st and 2nd mitosis or 2 cell-stage duration) and P3 (time between 2nd and 3rd mitosis or 3 cell-stage duration) Automatized predictive model Not suitable to blastocyst evaluation 375
Milewski et al., 2015 Time-lapse Non-
invasive
Human Day 5 NA Based on time of cell divisions (2 and 5 blastomeres) and interval between 2nd and 3rd divisions, it was proposed a multivariate predictive model Evaluation of morphokinetics parameters could provide data encompassing a long time frame of embryo development. This is the main advantage of the method, i.e. the opportunity to observe the embryo almost continuously The method considers only morphokinetic parameters - such as the relative and absolute times of cell division – on the impact of the embryo capacity to reach the blastocyst stage 162
Wong et al., 2010 Image
analysis
algorithm
Non-
invasive
Human Day 2 NA First algorithm attempt to embryo development automatized analysis. Could predict the blastocyst stage of development Automatized analysis of parameters Unable to discriminate parameters to predict the development up to blastocyst and its quality 242
Santos Filho et al., 2012 Support Vector Machine Non-
invasive
Human Blastocyst NA Potential method to automatized embryo classification discriminating quality parameters of inner cell mass and trophectoderm Method based only on the blastocyst image (numerical data mined from it with more discriminatory parameters than visual morphology assessment by human beings) Semi-automatic method was obtained and a fully automatized method should be achieved 73
van Loendersloot et al., 2014 Logistic
regression
Non-invasive Human Day 3 Embryonic morphology Early cleavage, blastomere number on days 2 and 3, morphologic pointing and presence of a morula no Day 3 of culture Method capable to distinguish embryos with high implantation potential from those with moderated or low potential   6021
Chen et al., 2016 Data mining to produce a computer-assisted scoring system based on multivariable logistic regression and multivariate adaptative regression spline Non-
invasive
Human Day 1,2 and 3 Embryonic
morphology
Point grading system Improvement on the generalization of the current predictive models Promising approach although
still experimental
871
Matos et al., 2014a Artificial neural network Non-
invasive
Mouse Blastocyst Embryonic morphology To avoid the subjectivity of the assessment done by a human examiner Classification systems fully based on software Needs an embryologist to manually to obtain numerical parameters from the embryo image 98
Matsuura et al., 2010 Blastocyst quality score Non-
invasive
Human Blastocyst NA New pointing system Numerical classification system based on the Gardner & Schoolcraft (1999) criteria There is a requirement for a huge number of embryos to produce statistical significance 220
Tejera et al., 2012 Oxygen consumption measurement Non-
invasive
Human Day 3 NA Oxygen consumption rate was associated with potential implantation and embryo quality Technique used as a complementary parameter to determine the embryo to be chosen Not useful to predict implantation rates. The causes of this lack of predictability is the clinical relevance of other variables that are related to embryo quality 84
Thompson et al., 2016 Multi-spectral imaging to evaluate the endogenous auto fluorescence Non-
invasive
Human and Bovine Early embryo stages Diversity of techniques The authors are trying to correlate the observed pattern of auto fluorescence with metabolic profile of the embryo. The aim is to predict the embryo quality during development of early embryos High resolution imaging (single embryo), real time and non-invasive method that could be associated with others (e.g., traditional morphological evaluation) besides computer based techniques. It is a current promise to determine the intracellular metabolic activity Experimental technique under evaluation ND
López-Damián et al., 2008 Transmission electron microscopy Lethal Bovine Blastocyst NA Demonstrated the sub-cellular variation of the embryos classified as fair grade by optical light microscopy and by stereomicroscopy Validated the accuracy of the IETS proposed system of embryo classification Unable to evaluate an embryo intended to be transferred to the uterus, just to validate the accuracy of a technique on sub-cellular aspects 30
Legend: Nature - invasiveness of the technique employed; Embryo stage – range of stages where the embryo was suitable or was used in the study; Compared to what traditional technique – when it was the case - that a new proposed technique had its efficacy compared to a traditional and well established one; On what parameters – when there was such comparison, did it occur, if not the case, in what primary parameters the authors evaluated the embryos; Sample size – the quantity of embryos used on the study; NA – not available; ND – not determined.