Choosing the best embryo by time lapse versus standard morphology
2014; Elsevier BV; Volume: 103; Issue: 2 Linguagem: Inglês
10.1016/j.fertnstert.2014.11.003
ISSN1556-5653
AutoresKirstine Kirkegaard, Aishling Ahlström, Hans Jakob Ingerslev, Thorir Hardarson,
Tópico(s)Reproductive Health and Technologies
ResumoWithin the past few years the morphological evaluation of in vitro fertilized embryos has been extended to include continuous surveillance, enabled by the introduction of time-lapse incubators developed specifically for IVF treatment. As a result time-lapse monitoring has been implemented in many clinics worldwide. The proposed benefits compared with culture in a standard incubator and fixed time-point evaluation are uninterrupted culture, a flexible workflow in the laboratory, and improved embryo selection. The latter is based on the reasonable assumption that more frequent observations will provide substantially more information on the relationship between development, timing, and embryo viability. Several retrospective studies have confirmed a relationship between time-lapse parameters and embryo viability evaluated by developmental competence, aneuploidy, and clinical pregnancy. Furthermore a much anticipated randomized study has shown improved pregnancy rates (PRs) after culture in a time-lapse incubator combined with selection using a hierarchical time-lapse selection model. At present this is the only randomized study on possible benefits of time lapse in human embryology. Strict evidence may still seem too weak to introduce time lapse in routine clinical setting. This aim of this review is therefore to perform a balanced discussion of the evidence for time-lapse monitoring. Within the past few years the morphological evaluation of in vitro fertilized embryos has been extended to include continuous surveillance, enabled by the introduction of time-lapse incubators developed specifically for IVF treatment. As a result time-lapse monitoring has been implemented in many clinics worldwide. The proposed benefits compared with culture in a standard incubator and fixed time-point evaluation are uninterrupted culture, a flexible workflow in the laboratory, and improved embryo selection. The latter is based on the reasonable assumption that more frequent observations will provide substantially more information on the relationship between development, timing, and embryo viability. Several retrospective studies have confirmed a relationship between time-lapse parameters and embryo viability evaluated by developmental competence, aneuploidy, and clinical pregnancy. Furthermore a much anticipated randomized study has shown improved pregnancy rates (PRs) after culture in a time-lapse incubator combined with selection using a hierarchical time-lapse selection model. At present this is the only randomized study on possible benefits of time lapse in human embryology. Strict evidence may still seem too weak to introduce time lapse in routine clinical setting. This aim of this review is therefore to perform a balanced discussion of the evidence for time-lapse monitoring. Discuss: You can discuss this article with its authors and with other ASRM members at Reliable selection of embryos with the highest developmental competence is a prerequisite for successful IVF treatment. Current embryo assessment is based on development rate and morphological features as evaluated under a microscope at certain, distinct time-points. Although embryo grading schemes vary between fertility clinics, most laboratories grade the cleavage stage embryo on the degree of fragmentation, presence and number of nuclei and size, number and symmetry of blastomeres per embryo (1Hardarson T. Hanson C. Sjogren A. Lundin K. Human embryos with unevenly sized blastomeres have lower pregnancy and implantation rates: indications for aneuploidy and multinucleation.Hum Reprod. 2001; 16: 313-318Google Scholar, 2Pickering S.J. Taylor A. Johnson M.H. Braude P.R. An analysis of multinucleated blastomere formation in human embryos.Hum Reprod. 1995; 10: 1912-1922Google Scholar, 3Racowsky C. Vernon M. Mayer J. Ball G.D. Behr B. Pomeroy K.O. et al.Standardization of grading embryo morphology.J Assist Reprod Genet. 2010; 27: 437-439Google Scholar, 4Scott L. Finn A. O'Leary T. McLellan S. Hill J. Morphologic parameters of early cleavage-stage embryos that correlate with fetal development and delivery: prospective and applied data for increased pregnancy rates.Hum Reprod. 2007; 22: 230-240Google Scholar, 5Steer C.V. Mills C.L. Tan S.L. Campbell S. Edwards R.G. The cumulative embryo score: a predictive embryo scoring technique to select the optimal number of embryos to transfer in an in-vitro fertilization and embryo transfer programme.Hum Reprod. 1992; 7: 117-119Google Scholar, 6Ziebe S. Petersen K. Lindenberg S. Andersen A.G. Gabrielsen A. Andersen A.N. Embryo morphology or cleavage stage: how to select the best embryos for transfer after in-vitro fertilization.Hum Reprod. 1997; 12: 1545-1549Google Scholar). Blastocysts are evaluated with regard to the expansion of the blastocoel and the number and cohesiveness of cells in the inner cell mass (ICM) and trophectoderm (TE) (7Gardner D.K. Surrey E. Minjarez D. Leitz A. Stevens J. Schoolcraft W.B. Single blastocyst transfer: a prospective randomized trial.Fertil Steril. 2004; 81: 551-555Google Scholar). Standardized timing of observations is critical (8ESHRE/ALPHAThe Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting.Hum Reprod. 2011; 26: 1270-1283Google Scholar). As morphology and developmental competence is not firmly correlated, morphological assessment has limited predictive value in the identification of the most viable embryos (8ESHRE/ALPHAThe Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting.Hum Reprod. 2011; 26: 1270-1283Google Scholar). This might be explained to some extent by the dependence on timing of the observations (9Montag M. Liebenthron J. Koster M. Which morphological scoring system is relevant in human embryo development?.Placenta. 2011; 32: S252-S256Google Scholar) and the high degree of interobserver and intraobserver variability (10Paternot G. Wetzels A.M. Thonon F. Vansteenbrugge A. Willemen D. Devroe J. et al.Intra- and interobserver analysis in the morphological assessment of early stage embryos during an IVF procedure: a multicentre study.Reprod Biol Endocrinol. 2011; 9: 127Google Scholar, 11Ruiz de Assin R. Clavero A. Gonzalvo M.C. Ramirez J.P. Zamora S. Fernandez A. et al.Comparison of methods to determine the assigned value in an external quality control programme for embryo evaluation.Reprod Biomed Online. 2009; 19: 824-829Google Scholar, 12Arce J.C. Ziebe S. Lundin K. Janssens R. Helmgaard L. Sorensen P. Interobserver agreement and intraobserver reproducibility of embryo quality assessments.Hum Reprod. 2006; 21: 2141-2148Google Scholar). Models based on sequential early embryo parameters in combination with specific time intervals of inspection have been shown to improve selection and implantation rates (13Nagy Z.P. Dozortsev D. Diamond M. Rienzi L. Ubaldi F. Abdelmassih R. et al.Pronuclear morphology evaluation with subsequent evaluation of embryo morphology significantly increases implantation rates.Fertil Steril. 2003; 80: 67-74Google Scholar, 14Van Loendersloot L. van Wely M. van der Veen F. Bossuyt P. Repping S. Selection of embryos for transfer in IVF: ranking embryos based on their implantation potential using morphological scoring.Reprod Biomed Online. 2014; 29: 222-230Google Scholar, 15Finn A. Scott L. O'Leary T. Davies D. Hill J. Sequential embryo scoring as a predictor of aneuploidy in poor-prognosis patients.Reprod Biomed Online. 2010; 21: 381-390Google Scholar). Therefore it is reasonable to assume that more frequent observations will provide substantially more information on the relationship between development and timing and thereafter embryo viability. This assumption forms the theoretical basis of the potential benefits of time-lapse monitoring (TLM) in human IVF embryo selection. An increasing number of studies report a correlation between timing of key events and implantation potential or surrogate end points such as aneuploidy and development potential. Yet, timing of development depends presumably on both culture conditions, treatment and patient populations, which might complicate the uncritical transferability of any model from one setting to another (16Ciray H.N. Aksoy T. Goktas C. Ozturk B. Bahceci M. Time-lapse evaluation of human embryo development in single versus sequential culture media—a sibling oocyte study.J Assist Reprod Genet. 2012; 29: 891-900Google Scholar, 17Cruz M. Garrido N. Gadea B. Munoz M. Perez-Cano I. Meseguer M. Oocyte insemination techniques are related to alterations of embryo developmental timing in an oocyte donation model.Reprod Biomed Online. 2013; 27: 367-375Google Scholar, 18Freour T. Dessolle L. Lammers J. Lattes S. Barriere P. Comparison of embryo morphokinetics after in vitro fertilization-intracytoplasmic sperm injection in smoking and nonsmoking women.Fertil Steril. 2013; 99: 1944-1950Google Scholar, 19Kirkegaard K. Hindkjaer J.J. Ingerslev H.J. Effect of oxygen concentration on human embryo development evaluated by time-lapse monitoring.Fertil Steril. 2013; 99: 738-744.e4Google Scholar, 20Kirkegaard K. Hindkjaer J.J. Ingerslev H.J. Hatching of in vitro fertilized human embryos is influenced by fertilization method.Fertil Steril. 2013; 100: 1277-1282Google Scholar, 21Munoz M. Cruz M. Humaidan P. Garrido N. Perez-Cano I. Meseguer M. Dose of recombinant FSH and oestradiol concentration on day of HCG affect embryo development kinetics.Reprod Biomed Online. 2012; 25: 382-389Google Scholar, 22Munoz M. Cruz M. Humaidan P. Garrido N. Perez-Cano I. Meseguer M. The type of GnRH analogue used during controlled ovarian stimulation influences early embryo developmental kinetics: a time-lapse study.Eur J Obstet Gynecol Reprod Biol. 2013; 168: 167-172Google Scholar). The aim of this review is to discuss the evidence regarding time lapse as a selection method and the role of TLM in the future assisted reproductive technology (ART) laboratory. An increasing number of studies suggest that timing of development differs between embryos with full developmental potential and those with no or limited potential. Based mostly on observational studies, several putative markers of viability have been suggested. Time-lapse variables identified in the literature as positive or negative predictors of development, aneuploidy, or pregnancy are summarized in Table 1, Table 2, Table 3. The end points vary greatly and the embryo populations are heterogeneous, which complicate comparisons between the studies. Only a few of the studies have adjusted for, or evaluated, known or potential confounders. Although almost all of the various parameters that are possible to measure have been proposed as candidate markers of viability, only a few clinically applicable models have been proposed (23Conaghan J. Chen A.A. Willman S.P. Ivani K. Chenette P.E. Boostanfar R. et al.Improving embryo selection using a computer-automated time-lapse image analysis test plus day 3 morphology: results from a prospective multicenter trial.Fertil Steril. 2013; 100: 412-419.e5Google Scholar, 24Meseguer M. Herrero J. Tejera A. Hilligsoe K.M. Ramsing N.B. Remohi J. The use of morphokinetics as a predictor of embryo implantation.Hum Reprod. 2011; 26: 2658-2671Google Scholar, 25Campbell A. Fishel S. Bowman N. Duffy S. Sedler M. Thornton S. Retrospective analysis of outcomes after IVF using an aneuploidy risk model derived from time-lapse imaging without PGS.Reprod Biomed Online. 2013; 27: 140-146Google Scholar). The end points for prediction models can, in principle, be divided into three categories: prediction of implantation, prediction of aneuploidy, and prediction of developmental competence, mainly blastocyst development. Figure 1 lists examples of time intervals identified as optimal for these three end points.Table 1Studies evaluating blastocyst development.StudyNo. of embryosEnd point(s)Predictive parametersSource of embryosPayne et al., 1997 74Payne D. Flaherty S.P. Barry M.F. Matthews C.D. Preliminary observations on polar body extrusion and pronuclear formation in human oocytes using time-lapse video cinematography.Hum Reprod. 1997; 12: 532-541Google Scholar30Day 3 quality (transfer/freeze or not)No difference in mean timings. Difference in variation in timing of PB extrusion and PN appearance and abuttalLemmen et al., 2008 71Lemmen J.G. Agerholm I. Ziebe S. Kinetic markers of human embryo quality using time-lapse recordings of IVF/ICSI-fertilized oocytes.Reprod Biomed Online. 2008; 17: 385-391Google Scholar102Blastomere number on day 2. Images/5 minFirst division (t2), PN breakdownIVF/ICSIWong et al., 2010 39Wong C.C. Loewke K.E. Bossert N.L. Behr B. de Jonge C.J. Baer T.M. et al.Non-invasive imaging of human embryos before embryonic genome activation predicts development to the blastocyst stage.Nat Biotechnol. 2010; 28: 1115-1121Google Scholar100Blastocyst/nonblastocysts day 5/6Duration of the first cytokinesis, duration of the 2- and 3-cell stageFrozen/thawed surplus embryos IVFHashimoto et al., 2012 36Hashimoto S. Kato N. Saeki K. Morimoto Y. Selection of high-potential embryos by culture in poly(dimethylsiloxane) microwells and time-lapse imaging.Fertil Steril. 2012; 97: 332-337Google Scholar80Blastocyst score 96 and 120 h after fertilizationHigh/low scoreTiming of the 7/8-cell stage. Duration of 3-cell stage and third cleavage (t8-t5)Frozen/thawed surplus embryos IVF and ICSI, 5% O2Cruz et al., 2012 34Cruz M. Garrido N. Herrero J. Perez-Cano I. Munoz M. Meseguer M. Timing of cell division in human cleavage-stage embryos is linked with blastocyst formation and quality.Reprod Biomed Online. 2012; 25: 371-381Google Scholar834Blastocyst score on day 5/6High/low qualityTiming of 4-cell stage (t4), duration of the 3-cell stage (s2), morula, uneven blastomeres, direct cleavage to 3 cellsDonor oocytes, 20% O2, ICSINonselectedDal Canto et al., 2012 35Dal Canto M. Coticchio G. Mignini Renzini M. de Ponti E. Novara P.V. Brambillasca F. et al.Cleavage kinetics analysis of human embryos predicts development to blastocyst and implantation.Reprod Biomed Online. 2012; 25: 474-480Google Scholar459Expandend/nonexpanded blastocysts on day 5All divisions and durations of cellular stages except first division (t2)Surplus, nonselected IVF/ICSI patients 5% O2Hlinka et al., 2012 37Hlinka D. Kalatova B. Uhrinova I. Dolinska S. Rutarova J. Rezacova J. et al.Time-lapse cleavage rating predicts human embryo viability.Physiol Res. 2012; 61: 513-525Google Scholar180Blastocyst developmentTime intervals for cleavage cycles and interphases (timely/untimely)Low positive but high negative predictive valueICSI, 20% O2, nonselected groupConaghan et al., 2013 23Conaghan J. Chen A.A. Willman S.P. Ivani K. Chenette P.E. Boostanfar R. et al.Improving embryo selection using a computer-automated time-lapse image analysis test plus day 3 morphology: results from a prospective multicenter trial.Fertil Steril. 2013; 100: 412-419.e5Google Scholar1,233Blastocyst quality (freeze/transfer)Duration of 2- and 3- cell stageDonor/infertile AFC ≥12, FSH <10 IU/mL, ≥8 2PN oocytesKirkegaard et al., 2013 38Kirkegaard K. Kesmodel U.S. Hindkjaer J.J. Ingerslev H.J. Time-lapse parameters as predictors of blastocyst development and pregnancy outcome in embryos from good prognosis patients: a prospective cohort study.Hum Reprod. 2013; 28: 2643-2651Google Scholar571High quality blastocystDuration of the first cytokinesis, 3-cell stage, direct cleavageProspective cohort (maternal age 7 oocytes), ICSI, 5% O2Note: AFC = antral follicle; ICSI = intracytoplasmic sperm injection; PB = polar body; PN = pronuclei. Open table in a new tab Table 2Studies evaluating implantation/pregnancy.StudyNo. of embryosEnd point(s)Predictive parametersSource of embryosLemmen et al., 2008 71Lemmen J.G. Agerholm I. Ziebe S. Kinetic markers of human embryo quality using time-lapse recordings of IVF/ICSI-fertilized oocytes.Reprod Biomed Online. 2008; 17: 385-391Google Scholar19 (6 implanted)Pregnancy, day 2 transfer SETSynchrony in appearance of nuclei after first cleavageIVF/ICSIMeseguer et al., 2011 24Meseguer M. Herrero J. Tejera A. Hilligsoe K.M. Ramsing N.B. Remohi J. The use of morphokinetics as a predictor of embryo implantation.Hum Reprod. 2011; 26: 2658-2671Google Scholar247 (61 implanted)Pregnancy (FHB), transfer on day 3 (1–3 embryos) Non-SETTime ranges for division to 5 cells (t5), duration of the 2-and 3-cell stage + exclusion variables, duration of 2-cell stage <5 h, MN, uneven blastomeres (2-cell stage)Mixture of donated oocytes and standard, nonselected group ICSI, 20% O2Azzarello et al., 2012 73Azzarello A. Hoest T. Mikkelsen A.L. The impact of pronuclei morphology and dynamicity on live birth outcome after time-lapse culture.Hum Reprod. 2012; 27: 2649-2657Google Scholar159 (46 implanted)Pregnancy (live birth), transfer day 2Non-SETPN breakdownProspective cohort (maternal age <40 y, male infertility factor), ICSI, 5% O2Cruz et al., 2012 34Cruz M. Garrido N. Herrero J. Perez-Cano I. Munoz M. Meseguer M. Timing of cell division in human cleavage-stage embryos is linked with blastocyst formation and quality.Reprod Biomed Online. 2012; 25: 371-381Google Scholar120 (63 implanted)Pregnancy (FHB)Non-SETNoneDonor oocytes, 20% O2, ICSIDal Canto et al., 2012 35Dal Canto M. Coticchio G. Mignini Renzini M. de Ponti E. Novara P.V. Brambillasca F. et al.Cleavage kinetics analysis of human embryos predicts development to blastocyst and implantation.Reprod Biomed Online. 2012; 25: 474-480Google Scholar124 (19 implanted)Pregnancy, day 3/5 transferNon-SETTime-point of the 8-cell stageNonselected IVF/ICSI patients 5% O2Hlinka et al., 2012 37Hlinka D. Kalatova B. Uhrinova I. Dolinska S. Rutarova J. Rezacova J. et al.Time-lapse cleavage rating predicts human embryo viability.Physiol Res. 2012; 61: 513-525Google Scholar114 (28 implanted)Pregnancy (FHB), transfer day 5SETTime-intervals for cleavage cycles and interphases (timely/untimely)Low positive but high negative predictive valueICSI, 20% O2, nonselected groupKirkegaard et al., 2013 38Kirkegaard K. Kesmodel U.S. Hindkjaer J.J. Ingerslev H.J. Time-lapse parameters as predictors of blastocyst development and pregnancy outcome in embryos from good prognosis patients: a prospective cohort study.Hum Reprod. 2013; 28: 2643-2651Google Scholar84 (26 implanted)Pregnancy (FHB), transfer day 6SETNone (duration of the first cytokinesis, 3-cell stage, direct cleavage was evaluated)Prospective cohort (maternal age 7 oocytes), ICSI, 5% O2Aguilar et al., 2014 72Aguilar J. Motato Y. Escriba M.J. Ojeda M. Munoz E. Meseguer M. The human first cell cycle: impact on implantation.Reprod Biomed Online. 2014; 28: 475-484Google Scholar899 (212 implanted)Pregnancy (FHB)Non-SETTime of the second PB extrusion, time from pronuclear appearance to pronuclear fading, and the time of PN fadingDonor oocytes, ICSI, 20% O2Rubio et al., 2014 30Rubio I. Galan A. Larreategui Z. Ayerdi F. Bellver J. Herrero J. et al.Clinical validation of embryo culture and selection by morphokinetic analysis: a randomized, controlled trial of the EmbryoScope.Fertil Steril. 2012; 98: 1458-1463Google Scholar843Pregnancy (FHB), transfer day 3/5Non-SETRCTTime ranges for division to 5 cells (t5), duration of the 2-and 3-cell stage + exclusion variables, duration of 2-cell stage 36 y (n = 102), >2 failed IVF cycles (n = 16), or >2 spontaneous abortions (n = 20)Note: a-CGH = array CGH; MN = multi-nucleation; PGS = preimplantation genetic screening; q-PCR = quantitative polymerase chain reaction; SNP = single-nucleotide polymorphism microarray. Open table in a new tab Note: AFC = antral follicle; ICSI = intracytoplasmic sperm injection; PB = polar body; PN = pronuclei. Note: FHB = fetal heart beat; ICSI = intracytoplasmic sperm injection; MN = multi-nucleation; PB = polar body; PN = pronuclei; RCT = randomized control trial; SET = single ET. Note: a-CGH = array CGH; MN = multi-nucleation; PGS = preimplantation genetic screening; q-PCR = quantitative polymerase chain reaction; SNP = single-nucleotide polymorphism microarray. The first published model aimed at predicting implantation potential was a hierarchical ranking model that used morphological observations and kinetic timings (24Meseguer M. Herrero J. Tejera A. Hilligsoe K.M. Ramsing N.B. Remohi J. The use of morphokinetics as a predictor of embryo implantation.Hum Reprod. 2011; 26: 2658-2671Google Scholar). Embryos originated from infertile patients and oocyte donors. The study (24Meseguer M. Herrero J. Tejera A. Hilligsoe K.M. Ramsing N.B. Remohi J. The use of morphokinetics as a predictor of embryo implantation.Hum Reprod. 2011; 26: 2658-2671Google Scholar) reported combined baseline data for 522 embryos as a result of intracytoplasmic sperm injection (ICSI) transferred to 247 patients, but to correlate the time-lapse observations to clinical outcome the analysis was restricted to include embryos with known implantation. The model was therefore based on 247 embryos from an unknown number of cycles, consisting of a mixture of transfer of single and multiple embryos. No baseline data were made available that allowed for an evaluation of the distribution of potential confounders for the implanted and nonimplanted group of the embryos and patients included in the model. Morphokinetic data were obtained using the EmbryoScope and the timing of cellular divisions up to five cells were recorded. Median values showed no significant statistical difference between the implanted and nonimplanted embryos, except for four-cell stage (t4)–t3 (s2). The group of implanted embryos displayed a more narrow distribution of timings with a smaller variance compared with nonimplanted embryos, which encouraged the investigators to define optimal time intervals based on quartiles for all annotated parameters, followed by a logistic regression analysis to identify the most predictive parameters. The result was a hierarchical model, where morphologically poor embryos were discarded after an initial screening, followed by a sequential application of the identified criteria. The exclusion criteria were direct cleavage from one to three cells, uneven blastomere size at the two-cell stage, and multinucleation at the four-cell stage. Then time to the five-cell stage, time interval between second and third mitosis (s2) and time interval between first and second mitosis (cc2) were used to discriminate between embryos in or outside of the defined optimal ranges. This model of ranking embryos had a better predictive value than morphology alone (area under the curve 0.72 compared with 0.64), although no statistical difference in implantation rate was found between embryos in the highest scoring category compared with embryos of highest morphological grade according to classic static scores (24Meseguer M. Herrero J. Tejera A. Hilligsoe K.M. Ramsing N.B. Remohi J. The use of morphokinetics as a predictor of embryo implantation.Hum Reprod. 2011; 26: 2658-2671Google Scholar). The strength of the study was evaluation of clinical pregnancy as the end point, which would have been further strengthened with single ETs. This type of model, where embryos are ranked rather than grouped into usable and nonusable, furthermore eliminates the risk that misclassification results in discarding viable embryos. The retrospective design and the lack of information regarding the distribution of confounders complicate the evaluation of whether the observed differences are directly correlated to differences in viability. In a subsequent study (26Meseguer M. Rubio I. Cruz M. Basile N. Marcos J. Requena A. Embryo incubation and selection in a time-lapse monitoring system improves pregnancy outcome compared with a standard incubator: a retrospective cohort study.Fertil Steril. 2012; 98: 1481-1489.e10Google Scholar) this model was tested on data collected retrospectively from 10 clinical sites. An impressive relative increase of 20.1% per ET for clinical PR was reported, compared with a control group of embryos cultured in conventional incubators and selected solely by static morphological grade. Embryos in both groups were cultured at atmospheric O2 concentration. As the investigators acknowledged, the improved clinical PR could also be explained by the potential better culture conditions supplied in a time-lapse incubator compared with the traditional incubator or selection bias. The hierarchical classification model is based on an initial deselection of embryos that are either clearly discardable or fulfill any of the morphokinetic exclusion criteria. In this model deselection thus outweighs selection. Interestingly, abrupt cleavage from one to three cells, defined by a short two-cell duration of less than 5 hours, has subsequently been shown to be a strong negative marker of implantation (27Rubio I. Kuhlmann R. Agerholm I. Kirk J. Herrero J. Escriba M.J. et al.Limited implantation success of direct-cleaved human zygotes: a time-lapse study.Fertil Steril. 2012; 98: 1458-1463Google Scholar). Direct cleavage to three cells constitutes a deviation from the normal cell cycle and uneven cleavage has previously been associated with underlying chromosomal aberrations (28Session 65—ART.Hum Reprod. 2006; 21: i100-i102Google Scholar). Other types of atypical early embryo cleavage have in a retrospective study been associated to implantation failure, but the findings remain to be validated in a larger set of embryos with known implantation (29Athayde Wirka K. Chen A.A. Conaghan J. Ivani K. Gvakharia M. Behr B. et al.Atypical embryo phenotypes identified by time-lapse microscopy: high prevalence and association with embryo development.Fertil Steril. 2014; 101: 1637-1648.e1–5Google Scholar). The negative association between aberrant division patterns and implantation may suggest that time lapse will facilitate deselection of embryos that on the day of transfer appear to be normal, yet this statement will require validation as well. Meseguer and colleagues, who are indeed pioneers in the introduction of TLM for IVF treatment, have recently followed up on the encouraging results from their retrospective studies, in a much anticipated randomized trial conducted by Rubio et al (30Rubio I. Galan A. Larreategui Z. Ayerdi F. Bellver J. Herrero J. et al.Clinical validation of embryo culture and selection by morphokinetic analysis: a randomized, controlled trial of the EmbryoScope.Fertil Steril. 2012; 98: 1458-1463Google Scholar) where the combination of uninterrupted embryo culture and the proposed hierarchical selection model was tested. Patients were randomized the day before oocyte retrieval to the study group (n = 444) where embryos were cultured in an incubator with time-lapse monitoring (n = 444) (EmbryoScope) or to the control group (n = 412) where embryos were cultured in a standard incubator. Embryos in the control group were selected for transfer by standard morphological scoring performed on day 3 or day 5. Embryos in the study group were selected for transfer based on the hierarchical selection model described previously. They considered the study blinded, as the gynecologists evaluating the outcome and the statisticians were blinded to treatment group. The primary, binary outcome was ongoing pregnancy, defined as the presence of fetal heartbeat detected by ultrasound in week 12. The study reported an odds ratio (OR) of 1.23 (95% confidenc
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