A novel system for rapid conversion of Gardner embryo grades to linear scale numeric variables

Published:January 12, 2023DOI:


      Research question

      Can Gardner embryo grades be converted to numeric interval variables to improve the incorporation of embryo grading in statistical analyses?


      An equation that can be used to convert Gardner embryo grades to regular interval scale variables was developed: the numerical embryo quality scoring index (NEQsi). The NEQsi system was then validated with a retrospective chart analysis assessing IVF cycles (n = 1711) conducted at a single Canadian fertility centre between 2014 and 2022. Gardner embryo grades on file were assigned using EmbryoScope and converted to NEQsi scores. Descriptive statistics, univariate logistic regressions and generalized estimating equations with cycle outcomes were prepared to demonstrate the relationship between NEQsi score and probability of pregnancy.


      NEQsi produces interval numerical scores that range from 2 to 11. Patient case files in which single embryo transfers occurred (n = 1711) were examined and the Gardner embryo grades on file were converted to NEQsi scores. NEQsi scores ranged from 3 to 11, with a median score of 9. A positive linear relationship existed between the NEQsi scores and the probability of pregnancy (as assessed by quantitative β-HCG). THe NEQsi score was a significant predictor of pregnancy (P < 0.001).


      Gardner embryo grades can be converted to interval variables and used directly statistical analyses.


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        • Ahlstrom A
        • Westin C
        • Reismer E
        • Wikland M
        • Hardarson T
        Trophectoderm morphology: An important parameter for predicting live birth after single blastocyst transfer.
        Hum. Reprod. 2011; 26: 3289-3296
        • Ai J
        • Jin L
        • Zheng Y
        • Yang P
        • Huang B
        • Dong X
        The morphology of inner cell mass is the strongest predictor of live birth after a frozen-thawed single embryo transfer.
        Front. Endocrinol. (Lausanne). 2021; 12621221
        • Alpha Scientists in Reproductive M
        • Embryology E.S.I.G.O
        The istanbul consensus workshop on embryo assessment: Proceedings of an expert meeting.
        Hum. Reprod. 2011; 26: 1270-1283
        • Dokras A
        • Sargent I.L
        • Barlow D.H
        Human blastocyst grading: An indicator of developmental potential?.
        Hum. Reprod. 1993; 8: 2119-2127
        • Ebner T
        • Tritscher K
        • Mayer R.B
        • Oppelt P
        • Duba H.C
        • Maurer M
        • Schappacher-Tilp G
        • Petek E
        • Shebl O
        Quantitative and qualitative trophectoderm grading allows for prediction of live birth and gender.
        J. Assist. Reprod. Genet. 2016; 33: 49-57
        • Gardner D
        • Schoolcraft W
        In vitro culture of human blastocysts.
        in: Jansen R Mortimer D. Towards Reproductive Certianty: Fertility and Genetics Beyond 1999. Parthenon Publishing, United Kingdom1999: 378-388
        • Gardner D.K
        • Weissman A
        • Howles C.M
        • Shoham Z
        Textbook of assisted reproductive techniques: Laboratory and clinical perspectives.
        2 ed. CRC Press Taylor & Francis Group, Boca Raton2004
        • Haas J
        • Meriano J
        • Bassil R
        • Barzilay E
        • Casper R.F
        Prolonged culture of blastocysts after thawing as a tool for improving prediction of success.
        J. Assist. Reprod. Genet. 2018; 35: 2195-2199
        • Hill M.J
        • Eubanks A.E
        • Csokmay J.M
        • Christy A.Y
        • Jahandideh S
        • Decherney A.H
        • Devine K
        • Levens E.D
        • Connell M.T
        Is transferring a lower-quality embryo with a good-quality blastocyst detrimental to the likelihood of live birth?.
        Fertil. Steril. 2020; 114: 338-345
        • Hill M.J
        • Richter K.S
        • Heitmann R.J
        • Graham J.R
        • Tucker M.J
        • Decherney A.H
        • Browne P.E
        • Levens E.D
        Trophectoderm grade predicts outcomes of single-blastocyst transfers.
        Fertil. Steril. 2013; 99 (1283-1289 e1)
        • Irani M
        • Reichman D
        • Robles A
        • Melnick A
        • Davis O
        • Zaninovic N
        • Xu K
        • Rosenwaks Z
        Morphologic grading of euploid blastocysts influences implantation and ongoing pregnancy rates.
        Fertil. Steril. 2017; 107: 664-670
        • Kim H.J
        • Park J.K
        • Eum J.H
        • Song H
        • Lee W.S
        • Lyu S.W
        Embryo selection based on morphological parameters in a single vitrified-warmed blastocyst transfer cycle.
        Reprod. Sci. 2021; 28: 1060-1068
        • Kirillova A
        • Lysenkov S
        • Farmakovskaya M
        • Kiseleva Y
        • Martazanova B
        • Mishieva N
        • Abubakirov A
        • Sukhikh G
        Should we transfer poor quality embryos?.
        Fertil. Res. Pract. 2020; 6: 2
        • Kragh M.F
        • Rimestad J
        • Berntsen J
        • Karstoft H
        Automatic grading of human blastocysts from time-lapse imaging.
        Comput. Biol. Med. 2019; 115103494
        • Lemeshow S
        • Sturdivant R
        • Hosmer D
        Applied logistic regression.
        3 ed. John Wiley & Sons, Inc, 2013
        • Li H
        • Xu X
        • Jing Y
        • Liu L
        • Wang Y
        Associations between a new day 4 embryo grading system and implantation rates in frozen embryo transfer (fet) cycles.
        Medicine (Baltimore). 2020; 99: e22676
        • Liao Q
        • Zhang Q
        • Feng X
        • Huang H
        • Xu H
        • Tian B
        • Liu J
        • Yu Q
        • Guo N
        • Liu Q
        • Huang B
        • Ma D
        • Ai J
        • Xu S
        • Li K
        Development of deep learning algorithms for predicting blastocyst formation and quality by time-lapse monitoring.
        Commun. Biol. 2021; 4: 415
        • Liu L
        • Li Y.H
        • Ding X.F
        • Geng Y.H
        • Chen C.Y
        • Gao Y
        Influence of blastocysts morphological score on pregnancy outcomes in frozen-thawed blastocyst transfers: A retrospective study of 741 cycles.
        J. Huazhong. Univ. Sci. Technolog. Med. Sci. 2014; 34: 750-754
        • Lou H
        • Li N
        • Guan Y
        • Zhang Y
        • Hao D
        • Cui S
        Association between morphologic grading and implantation rate of euploid blastocyst.
        J. Ovarian. Res. 2021; 14: 18
        • Meriano J
        • Clark C
        • Cadesky K
        • Laskin C.A
        Binucleated and micronucleated blastomeres in embryos derived from human assisted reproduction cycles.
        Reprod. Biomed. Online. 2004; 9: 511-520
        • Mizuno S
        • Matsumoto H
        • Hashimoto S
        • Brahmajosyula M
        • Ohgaki A
        • Tarui S
        • Matoba M
        • Satoh M
        • Fukuda A
        • Morimoto Y
        A novel embryo quality scoring system to compare groups of embryos at different developmental stages.
        J. Assist. Reprod. Genet. 2021; 38: 1123-1132
        • Morbeck D.E
        Blastocyst culture in the era of pgs and freezealls: Is a 'c' a failing grade?.
        Hum Reprod. Open. 2017; 2017: hox017
        • Pierson H.E
        • Cadesky K
        • Meriano J
        • Invik J
        • Laskin C.A
        • Pierson R.A
        Ultrasound based endometrial receptivity scoring accurately identifies ivf cycles with low probability of pregnancy.
        Fertil. Steril. 2021; 116: E-312
        • Racowsky C
        • Vernon M
        • Mayer J
        • Ball G.D
        • Behr B
        • Pomeroy K.O
        • Wininger D
        • Gibbons W
        • Conaghan J
        • Stern J.E
        Standardization of grading embryo morphology.
        Fertil. Steril. 2010; 94: 1152-1153
        • Rehman K.S
        • Bukulmez O
        • Langley M
        • Carr B.R
        • Nackley A.C
        • Doody K.M
        • Doody K.J
        Late stages of embryo progression are a much better predictor of clinical pregnancy than early cleavage in intracytoplasmic sperm injection and in vitro fertilization cycles with blastocyst-stage transfer.
        Fertil. Steril. 2007; 87: 1041-1052
      1. Research, C.I.O.H ., Canada, N.S.a.E.R.C.O ., Canada, S.S.a.H.R.C.O ., 2018. Tri-council policy statement: Ethical conduct for research involving humans.

        • Scott L
        • Alvero R
        • Leondires M
        • Miller B
        The morphology of human pronuclear embryos is positively related to blastocyst development and implantation.
        Hum. Reprod. 2000; 15: 2394-2403
        • Shi W
        • Jin L
        • Liu J
        • Zhang C
        • Mi Y
        • Shi J
        • Wang H
        • Liang X
        Blastocyst morphology is associated with the incidence of monozygotic twinning in assisted reproductive technology.
        Am. J. Obstet. Gynecol. 2021; 225 (654 e1-654 e16)
        • Shi W
        • Zhang S
        • Zhao W
        • Xia X
        • Wang M
        • Wang H
        • Bai H
        • Shi J
        Factors related to clinical pregnancy after vitrified-warmed embryo transfer: A retrospective and multivariate logistic regression analysis of 2313 transfer cycles.
        Hum. Reprod. 2013; 28: 1768-1775
        • Stephenson E.L
        • Braude P.R
        • Mason C
        International community consensus standard for reporting derivation of human embryonic stem cell lines.
        Regen. Med. 2007; 2: 349-362
        • Storr A
        • Bilir E
        • Cooke S
        • Garrett D
        • Venetis C.A
        Fine-tuning blastocyst selection based on morphology: A multicentre analysis of 2461 single blastocyst transfers.
        Reprod. Biomed. Online. 2019; 39: 588-598
        • Thompson S.M
        • Onwubalili N
        • Brown K
        • Jindal S.K
        • Mcgovern P.G
        Blastocyst expansion score and trophectoderm morphology strongly predict successful clinical pregnancy and live birth following elective single embryo blastocyst transfer (eset): A national study.
        J. Assist. Reprod. Genet. 2013; 30: 1577-1581
        • Van Den Abbeel E
        • Balaban B
        • Ziebe S
        • Lundin K
        • Cuesta M.J
        • Klein B.M
        • Helmgaard L
        • Arce J.C
        Association between blastocyst morphology and outcome of single-blastocyst transfer.
        Reprod. Biomed. Online. 2013; 27: 353-361
        • Veeck L
        • Zaninovic N
        An atlas of human blastocysts.
        CRC Press, Boca Raton, FL2003
        • Wang W
        • Cai J
        • Liu L
        • Xu Y
        • Liu Z
        • Chen J
        • Jiang X
        • Sun X
        • Ren J
        Does the transfer of a poor quality embryo with a good quality embryo benefit poor prognosis patients?.
        Reprod. Biol. Endocrinol. 2020; 18: 97
        • Zhan Q
        • Sierra E.T
        • Malmsten J
        • Ye Z
        • Rosenwaks Z
        • Zaninovic N
        Blastocyst score, a blastocyst quality ranking tool, is a predictor of blastocyst ploidy and implantation potential.
        F. S. Rep. 2020; 1: 133-141
        • Zhang J
        • Huang J
        • Liu H
        • Wang B
        • Yang X
        • Shen X
        • Mao X
        • Wang Y
        • Kuang Y
        The impact of embryo quality on singleton birthweight in vitrified-thawed single blastocyst transfer cycles.
        Hum. Reprod. 2020; 35: 308-316
        • Zhao Y.Y
        • Yu Y
        • Zhang X.W
        Overall blastocyst quality, trophectoderm grade, and inner cell mass grade predict pregnancy outcome in euploid blastocyst transfer cycles.
        Chin. Med. J. (Engl). 2018; 131: 1261-1267


      Hannah Pierson earned her PhD in biochemistry and completed her post-doctoral fellowship in epithelial cell biology at the Johns Hopkins Medical Institute. She is a Senior Scientist with Synergyne ART Analytics Inc. Her research interests include advancing the boundaries of biomedical image interpretation technologies and the cellular dynamics of endometrium.
      Key message
      The Gardner embryo grading system provides insight into morphologic embryo quality. Alphanumeric grading, however, presents challenges in statistical analyses. The numerical embryo quality scoring index (NEQsi) facilitated conversion of embryo grades to interval variables for statistical purposes. A positive linear relationship was observed between NEQsi scores and probability of pregnancy.