人类种植前胚胎的染色体分析

核型分析是诊断人类胚胎染色体异常的常规方法 ,但是通过细胞遗传学方法对人类种植前胚胎进行染色体检测并不容易。因此分裂间期细胞核的荧光原位杂交 (FISH)就成为首选方法之一。体外受精 (IVF)种植前胚胎的 FISH和核型分析均表明 :胚胎的染色体异常率可高达 2 5 %～ 5 1%。FISH分析显示染色体异常最常见的情况是染色体嵌合 (2 2 %～ 2 4 % )和胚胎分裂紊乱 (7%～ 2 6 % )。虽然目前还不能应用以上方法对自然受精的胚胎进行检测 ,但是染色体嵌合以及胚胎分裂紊乱较高的发生率可以为我们合理的解释人类的月经周期自然妊娠率为什么如此之低 (2 5 % ) ,提供理论依据     

MLPA联合FISH检测自然流产绒毛组织中染色体嵌合现象

目的 应用多重连接探针扩增法(MLPA)亚端粒探针分析(Subtelomere Assay)联合荧光原位杂交(FISH)对自然流产绒毛进行遗传学分析,并探讨绒毛组织染色体嵌合现象的发生与自然流产的关系.方法 31例自然流产、16例IVF/ICSI治疗后流产、10例正常对照绒毛组织,同时进行细胞培养核型分析及MLPA联合FISH检测.结果 细胞培养核型分析与MLPA联合FISH检测的成功率分别为71.93%(41/57)、100%(57/57),两者差异有统计学意义(P<0.001);自然流产组绒毛染色体异常率61.29%(19/31),IVF/ICSI流产组绒毛染色体异常率56.25%(9/16),正常对照组为10%(1/10);正常对照组绒毛16、18、X、Y 3对染色体的平均嵌合率为98.6%±1.32%,以正常对照组3对染色体平均嵌合率-2SD为界限值下限统计嵌合发生率;自然流产组和IVF/ICSI流产组绒毛嵌合率分别为38.71%(12/31)、25%(4/16),高于正常对照组.结论 自然流产绒毛组织的染色体异常率、嵌合现象发生率均高,是导致胚胎自然流产的重要原因.     

一例嵌合型18三体少精子症患者精染色体分析及植入前遗传学诊断

目的 分析1例嵌合型18三体少精子患者精子18、X、Y染色体数目畸变并进行植入前遗传学诊断(preimplantation genetic djagnosis,PGD).方法 采用G带及荧光原位杂交(fluorescence in situ hybridjzation,FISH)对中期分裂相进行分析,应用三色探针CEP18、CEPY、Tel Xq/Yq对患者精子进行FISH分析,同时以1名染色体正常男性的正常精液作为对照,并对嵌合型18三体患者进行PGD.结果 患者精子18二体率、性染色体二体率和二倍体率分别为0.63%、0.94%和0.87%,与对照组相比(0.16%、0.35%、0.31%)差异有统计学意义.患者进行1个PGD周期的治疗、活检4个胚胎,移植正常的XY1818、XX1818各1胚胎后获得临床妊娠.结论 精子FISH分析可为其提供更准确的遗传咨询及指导植入前遗传学诊断,FISH-PGD可有效地应用于嵌合型18三体的植入前遗传学诊断.     

微阵列芯片比较基因组杂交技术在植入前遗传学诊断中的应用研究

目的 建立适用于植入前遗传学诊断的微阵列芯片比较基因组杂交技术(array comparative genomic hybridization,array CGH).方法 对以下3种来源的细胞进行array CGH分析:(1)经胰酶消化的核型分别为46,XX、46,XY、47,XX,+13的B2、C38、A1的3株人胚胎干细胞,分离后获取3～5个细胞;(2)在本中心进行体外受精与胚胎移植(in-vitro fertilization-embryo transfer,IVF-ET)的正常受精来源的废弃胚胎卵裂球;(3)源自5对罗氏或相互易位携带者的夫妻、在本中心进行植入前遗传学诊断的10个废弃胚胎,其中8个胚胎经荧光原位杂交(fluorescence in situ hybridization,FISH)诊断为异常,1枚无信号,1枚诊断正常但胚胎发育停滞.经全基因组扩增后,对扩增产物进行24sure V3或24sure+芯片检测,采用BlueFuse Multi软件进行数据分析.结果 (1)对来自B2、C38、A1系干细胞株的3～5个细胞进行array CGH分析,结果与核型鉴定一致;(2)对来自2枚正常受精胚胎的6个卵裂球的扩增产物行24sure V3分析,1枚胚胎的2个卵裂球分别为非整倍体和正常核型,另1枚胚胎的4个卵裂球中2个正常,另外2个均为-22,+13.用24sure+重复上述实验,其结果与前一致;(3)对来自染色体易位行植入前遗传学诊断的10枚胚胎进行array CGH分析,4枚胚胎在array CGH分析时与FISH诊断结果相符,其中2枚FISH与array CGH结果完全一致,2枚通过array CGH分析发现除FISH发现的异常外的其他多条染色体数目异常.1枚胚胎FISH检测无信号,而array CGH诊断为13三体.5枚与FISH诊断结果不符的胚胎中,1枚来自罗氏易位FISH诊断为13单体,两种array CGH芯片均诊断为14三体及其他多条染色体非整倍体改变,1枚胚胎碎片多且发育停滞(该易位患者另2枚胚胎诊断均相符),其余3枚结果不相符的胚胎均来源于染色体(p13;q11)的相互易位.结论 应用array CGH可同时完成对胚胎染色体结构检测及全染色体组非整倍体筛查,但在断裂点距离着丝粒位置较近的染色体1区的易位应选择分辨率高的24sure+芯片.     

内蒙古呼和浩特地区185例优生遗传咨询者FISH技术检测结果分析

目的评价荧光原位杂交(fluorescence in situ hybridization,FISH)诊断染色体非整倍体的临床价值。方法 FISH技术检测185例样本,临床诊断原因包括产前筛查高风险、B超检测异常、胚胎停育、外观异常等。将羊水细胞FISH检测结果与传统细胞核型分析方法进行比较。根据FISH结果结合临床诊断意见,评价FISH的临床应用价值。结果 1)FISH羊水样本检测88例,异常20例,其中79例作羊水细胞核型分析,检测结果与FISH相符率100%。2)绒毛组织样本检测72例,异常14例,人工流产与胚胎停育有正相关性。3)外周血检测20例,异常15例,检测结果与外周血核型分析结果一致。结论 FISH技术能快速准确检测染色体非整倍体异常,是传统细胞遗传学方法的有力辅助。     

一例罗伯逊易位携带者的胚胎植入前遗传学诊断

目的　探讨植入前遗传学诊断 (preimplantation genetic diagnosis,PGD)用于筛选罗伯逊易位携带者无遗传缺陷后代的可行性及风险。方法　 1对因男方携带易位 (13;14 )染色体并伴少、弱精的原发不孕夫妇 ,经激素超促排卵和单精子卵胞浆内注射 (intracytoplasmic sperm injection,ICSI)进行体外受精(in vitro fertilization,IVF) ,当胚胎发育到 6～ 8细胞阶段 (受精后第 3天 )时 ,用酸化法活检 ,从每个胚胎中取出单个分裂球 ,用 L SI 13q和 Tel 14 q探针进行荧光原位杂交 (fluorescence in situ hybridization,FISH)检测 ,继续培养活检后的胚胎到第 2天 ,并选择正常胚胎移植 ,获临床妊娠后 ,于妊娠中期行羊水细胞染色体检查。结果　活检 10个胚胎 ,获得 8个 FISH诊断结果 :5 0 % (4/8)正常或平衡的胚胎 ,37.5 % (3/8)不平衡的胚胎 ,12 .5 % (1/8)不确定。将诊断正常或平衡的胚胎 3枚于活检第 2天移植入母体宫腔 ,获临床单胎妊娠 ,产前诊断证实胎儿核型为 4 6 ,XY,完全正常 ,现分娩一正常男婴。结论　需行辅助生殖技术治疗的患者 ,当携带有罗伯逊易位时 ,PGD用于筛除异常胚胎 ,解决患者的生育障碍、预防严重遗传病胎儿的产生具有重要价值。     

分子生物学技术检测自然流产绒毛染色体数目异常

目的分析检测自然流产绒毛常见染色体的非整倍体。方法本文对66例自然流产绒毛,用FISH(fluorescence in situ hybridization,FISH)技术,选用13,18,16,21,22,X和Y染色体特异性探针,分析流产绒毛这七种染色体非整倍状况。结果 66例中,异常共28例,占42.4%。其中3例为多倍体异常,2例性染色体多倍体异常,23例为非整倍体异常。结论 1.FISH技术能快速检测自然流产绒毛染色体的异常,胚胎染色体数目异常是自然流产的主要原因。2.高龄孕妇流产绒毛染色体数目异常率高于非高龄孕妇,但无统计学差异。     

CENP-A基因在自然流产染色体数目异常胚胎中的表达

目的探讨CENP-A表达在人类胚胎绒毛染色体分离中的作用。方法应用荧光原位杂交(fluorescence in situ hybridization,FISH)技术检测94例自然流产胚胎绒毛染色体数目,分别用q RT-PCR和Western blotting检测胚胎绒毛组织中CENP-A m RNA和蛋白质相对表达水平。结果 194例自然流产胚胎中检出异常结果病例数共48例,占总病例数的51.06%,其中阳性病例数30例,阳性率为31.91%。比较常见的异常类型有16三体、21三体、22三体、X单体和三倍体。2CENP-A m RNA在实验组和对照组表达水平差异无统计学意义(P0.05)。3异常组胚胎绒毛组织中CENP-A蛋白相对表达水平明显高于正常组,差异具有统计学意义(P0.05)。结论着丝粒蛋白CENP-A表达异常与染色体非整倍体引起的自然流产有关。     

高育龄妇女胚胎植入前21号染色体非整倍体检测

目的运用荧光原位杂交技术(fluorescent in situ hybridization,FISH)对生育过21三体患儿的高育龄妇女的胚胎进行植入前遗传学诊断,达到优生目的.方法应用FITC标记的21号着丝粒探针对生育过21三体患儿的高育龄妇女的胚胎活检后单个卵裂球进行遗传学检测,选择正常信号或携带者信号核型胚胎进行移植.结果常规单精子显微注射-胚胎移植(intracytoplasmic sperm injection,ICSI)后获取胚胎4个,活检优质胚胎3个,杂交后每个卵裂球均出现3个21号染色体完整信号,认为3个胚胎均为21三体异常胚胎,故建议放弃移植,从而成功避免了21三体患儿的出生.结论运用21号染色体着丝粒探针荧光原位杂交技术对生育过21三体患儿的高育龄妇女的胚胎进行植入前遗传学诊断是可行的,同时也是必要的,是避免非整倍体患儿出生的重要途径.     

人类种植前胚胎的染色体分析

核型分析是诊断人类胚胎染色体异常的常规方法，但是通过细胞遗传学方法对人类种植前胚胎进行染色体检测并不容易。因此分裂间期细胞核的荧光原位杂交（FISH）就成为首选方法之一。体外受精（IVF）种植前胚胎的FISH和核型分析均表明：胚胎的染色体异常率可高达25％－51％。FISH分析显示染色体异常最常见的情况是染色体嵌合的（22％－24％）和胚胎分裂紊乱（7％－26％）。虽然目前还不能应用以上方法对自然受精的胚胎进行检测，但是染色体嵌合以及胚胎分裂紊乱较高的发生率可以为我们合理的解释人类的月经周期自然妊娠率为什么如此低（25％），提供理论依据。     

Chromosomal mosaicism throughout human preimplantation development in vitro: incidence, type, and relevance to embryo outcome

BACKGROUND: A large percentage of in-vitro generated cleavage stage human embryos are chromosomally mosaic, consisting of both normal (diploid) and abnormal (non-diploid) cells. The present study characterized mosaicism at each stage of cleavage division and examined its effect on preimplantation development in vitro. METHODS: A total of 216 normally fertilized (two-pronucleate) embryos which were not selected for transfer to the patients were analysed for chromosomal abnormalities using multi-colour fluorescence in-situ hybridization DNA probes specific for three to five of nine different chromosomes (X, Y, 2, 7, 13, 16, 18, 21, 22). RESULTS: Overall, 48.1% of embryos were mosaic. The frequency of mosaic embryos increased from 15.2 to 49.4 to 58.1%, from the 2-4-cell to 5-8-cell to morula stages respectively, and the types of non-diploid cells detected were mostly aneuploid or chaotic. The incidence of mosaicism at the blastocyst stage was 90.9%; however, most of the mosaicism comprised diploid and polyploid cells. Arrested mosaic embryos had a higher incidence of chaotic abnormalities, and higher proportions of abnormal cells compared with the non-arrested group. CONCLUSIONS: Post-zygotic errors leading to mosaicism may occur, and persist throughout preimplantation development in vitro. Our results suggest that mosaicism involving multiple chromosomal imbalances and/or imbalances affecting a high proportion of cells in an embryo appear to impair development to the blastocyst stage.     

Detailed FISH analysis of day 5 human embryos reveals the mechanisms leading to mosaic aneuploidy

BACKGROUND: Fluorescence in situ hybridization (FISH) analysis has shown that human embryos display a high level of chromosomal mosaicism at all preimplantation stages. The aim of this study was to investigate the mechanisms involved by the use of two probes for each of three autosomes at different loci and to determine the true level of aneuploid mosaicism by excluding FISH artefacts. METHODS: Embryos were cultured in two different types of medium: group I were cultured in standard cleavage medium for up to day 5 and group II were cultured from day 3 to day 5 in blastocyst medium. Three rounds of FISH were performed. In round 1, the probes used were 1pTel, 11qTel and 18CEP; in round 2, the probes used were 1satII/III, 11CEP and 18qTel; in round 3, the probes used were 18CEP, XCEP and YCEP. RESULTS: A total of 21 embryos were analysed in each group. The FISH results revealed one uniformly diploid and 20 mosaic embryos for group I, and two uniformly diploid and 19 mosaic embryos for group II. The predominant type of mosaicism was diploid/aneuploid. The use of two different probes per autosome was able to distinguish FISH artefacts affecting 5% of nuclei from true single cell anomalies. CONCLUSIONS: Post-zygotic chromosome loss was the most common mechanism leading to aneuploidy mosaicism for both groups, followed by chromosome gain, with fewer examples of mitotic non-disjunction.     

The development of cytogenetically normal, abnormal and mosaic embryos: a theoretical model

Assisted reproduction and preimplantation genetic diagnosis (PGD) involve various complicated techniques, each of them with its own problems. However, the greatest problem with PGD for chromosome abnormalities is not of a technical nature but is a biological phenomenon: chromosomal mosaicism in the cleavage stage embryo. Here, we present a hypothetical, quantitative model for the development of chromosomally normal, abnormal and mosaic embryos. The arising of mosaicism in 2-8-cell embryos was described by a binomial probability model on the occurrence of mitotic events inducing chromosomal changes in the blastomeres. This model converted the 'mean' rate of mosaicism found in cross-sectional studies (60%) into an equal rate of mosaic embryos at arrival at the 8-cell stage (59.8%). The disappearance of > 90% of the mosaic embryos or the mosaicism itself from surviving embryos during the morula stage was explained by mitotic arrest of most of the mitotically changed cells under increasing cell cycle control. In our model, 25.9 and 14.3% of the embryos at the 8-cell stage are normal and abnormal respectively. The remaining 59.8% of the embryo shows mosaicism: 34.6% of abnormal/normal cells and 25.2% of abnormal/abnormal cells. The high proportion of abnormal and mosaic embryos together explains the high rate of abnormal laboratory findings in PGD for chromosomal abnormalities and aneuploidy screening. The poor representation of a 1- or 2-cell biopsy for the 7- or 6-cell post-biopsy embryo in the case of mosaicism explains the high rate of false-negative and false-positive results.     

Analysis of the evolution of chromosome abnormalities in human embryos from Day 3 to 5 using CGH and FISH

The use of interphase fluorescent in situ hybridization (FISH) has shown that a large number of human embryos exhibit chromosomal abnormalities in vitro. The most common abnormality is mosaicism which is seen in up to 50% of preimplantation embryos at all stages of development. In this study, comparative genomic hybridization (CGH) was used to analyse 1-2 cells biopsied on Day 3 of development while the rest of the embryo was cultured until Day 5. Embryos were spread on Day 5 and analysed by FISH using probe combinations that varied depending on the CGH result, to investigate the progress of any abnormalities detected on Day 3. A total of 37 frozen-thawed embryos were analysed in this study. One gave no CGH or FISH results and was excluded from analysis. Six embryos failed to give any FISH result as they were degenerating on Day 5. Thirty embryos provided results from both techniques. According to the CGH results, the embryos were divided into two groups; Group 1 had a normal CGH result (13 embryos) and Group 2 an abnormal CGH result (17 embryos). For Group 1, three embryos showed normal CGH and FISH results, while 10 embryos were mosaic after FISH analysis, with various levels of abnormalities. For Group 2, FISH showed that all embryos were mosaic or completely chaotic. The combination of CGH and FISH enabled the thorough investigation of the evolution of mosaicism and of the mechanisms by which it is generated. The main two mechanisms identified were whole or partial chromosome loss and gain. These were observed in embryos examined on both Day 3 and 5.     

Preimplantation genetic screening reveals a high incidence of aneuploidy and mosaicism in embryos from young women undergoing IVF

BACKGROUND: In order to assess the frequency of aneuploidy and mosaicism in embryos obtained from IVF patients aged <38 years, preimplantation genetic screening (PGS) was performed after biopsy of two blastomeres. Furthermore, the reliability of this diagnosis was assessed by performing reanalysis of the embryo on day 5. METHOD: The copy numbers of 10 chromosomes (1, 7, 13, 15, 16, 18, 21, 22, X and Y) were investigated by fluorescence in situ hybridization (FISH) analysis. Embryos that were found to be abnormal or of insufficient morphological quality were cultured until day 5 and reanalysed. Results obtained were compared to the day 3 blastomere analysis. RESULTS: After analysis of 196 embryos (one cell in 38% and two cells in 62%), only 36% of the embryos were found to be normal on day 3. After analysis of two blastomeres, 50% showed chromosomal mosaicism. Comparison of the FISH results from day 3 blastomeres and day 5 embryos yielded an overall cytogenetic confirmation rate of 54%. CONCLUSIONS: The rates of mosaicism and aneuploidy in these embryos from young IVF patients are similar to those published for older women. We found the best confirmation rate after a diagnosis based on two cells, where both blastomeres showed the same chromosomal abnormality. In contrast, after a mosaic diagnosis the confirmation rate was low. The present study provides the first detailed reanalysis data of embryos analysed by PGS and clearly demonstrates the impact of mosaicism on the reliability of the PGS diagnosis.     

Fluorescence in situ hybridization analysis of two blastomeres from day 3 frozen-thawed embryos followed by analysis of the remaining embryo on day 5

BACKGROUND: Chromosomal mosaicism in human embryos may give rise to false positive or false negative results in preimplantation genetic diagnosis for aneuploidy screening (PGD-AS). Therefore, we have investigated whether the results obtained from a 2-cell biopsy of frozen-thawed embryos and fluorescence in situ hybridization (FISH) analysis are representative for the chromosome constitution of the remaining embryo on day 5. METHODS: Cryopreserved day 3 embryos were thawed and from surviving embryos two blastomeres were biopsied. FISH analysis was performed for chromosomes 1, 7, 13, 15, 16, 18, 21, 22, X and Y. After biopsy, the embryos were cultured until day 5 and further analysed using the same probe panels. RESULTS: In all, 17 embryos were available with a diagnosis based on two blastomeres on day 3 and confirmatory studies on day 5. In 10 of these 17 cases the initial diagnosis could be confirmed. However, in only six cases cytogenetic results were concordant. Besides the 10 cases with a 'correct' diagnosis, there were six false positive results and one false negative, all involving mosaicism. CONCLUSIONS: Investigating the chromosomal constitution of two blastomere nuclei offers a good opportunity to study the incidence of chromosomal mosaicism in early embryo development. The confirmation rate of the results obtained on day 3 depends on the interpretation and is higher when considered from a clinical than from a cytogenetic point of view.     

大Y携带者不良孕产史与胚胎非整倍体率增高的关系

目的探讨1例有不良孕产史的大Y携带者的胚胎异常情况。方法1对有2次自然流产史的夫妇,男方染色体核型为46,XY,Yqh ,常规超促排卵和卵母细胞胞浆内单精子注射,受精后第3天和第4天进行胚胎活检,获取分裂球,采用18,X,Y三色着丝粒探针进行荧光原位杂交分析(FISH),第5天移植正常胚胎。异常胚胎及废弃胚胎所有分裂球第6天再次FISH确定胚胎核型。结果患者获卵19个,对其中13个M2期卵母细胞进行ICSI,12个受精,分裂11胚。10个胚胎获得明确诊断,其中4个正常胚胎,6个异常胚胎,异常发生率达60%。5个为女胚,其中1个正常核型,4个异常胚胎中2个为无序分裂,2个为嵌合体;5个为男胚,3个正常,2个异常胚胎中1个为无序分裂,1个为嵌合体。对染色体正常的1个女胚进行宫腔内移植,未获得妊娠。结论该例大Y患者胚胎非整倍体发生率增高可能是导致其不良孕产史的原因。     

Preimplantation genetic diagnosis and sperm analysis by fluorescence in-situ hybridization for the most common reciprocal translocation t(11;22).

In this study we describe the pre-clinical development and clinical application of preimplantation genetic diagnosis (PGD) by fluorescence in-situ hybridization (FISH) for two non-related carriers (one male and one female) of the most common balanced reciprocal translocation: t(11;22)(q25;q12). For the couple with the female carrier, enumeration of the sex chromosomes in the embryos was also indicated (husband: 47,XXY karyotype). Four-colour FISH analysis was performed on six blastomeres from three embryos. No embryo transfer was possible because all the embryos were unbalanced. Three PGD cycles, with two-colour FISH, were carried out for the couple with the male translocation carrier. A total of 35 embryos were biopsied and diagnosed by FISH; nine out of the 35 embryos (25. 7%) were normal and seven of them were transferred (two embryos from the first and four from the third cycle), six out of 35 embryos (17%) were unbalanced, three out of 35 embryos (5.7%) were triploid or polyploid, 10 out of 35 embryos (28.6%) were mosaic and seven out of 35 embryos (20%) were chaotic. Diagnosis failed in 2.9% of the embryos. The spermatozoa of the male carrier were also analysed using three-colour FISH. Only 29.1% of the sperm cells seemed to be balanced or normal. By choosing probes lying on both sides of the breakpoints and by using a combination of sub-telomeric or locus-specific probes and centromeric probes, the use of three-colour FISH enabled detection of all the imbalances in sperm and/or cleavage-stage embryos in the patients. This may improve risk assessment and genetic counselling in the future for translocation carriers.     

Chromosomally abnormal cells are not selected for the extra-embryonic compartment of the human preimplantation embryo at the blastocyst stage

BACKGROUND: Although well defined for embryos at cleavage stages, the occurrence and frequency of chromosomal aberrations in human blastocysts is relatively unknown. It has been reported that only one in four blastocysts is comprised totally of chromosomally normal cells. One of the selection mechanisms for the embryo proper to become free of these chromosomally abnormal cells would be to sequester them to the extra-embryonic compartment during development. The study aim was to investigate whether such a mechanism of selection exists in human preimplantation embryos. METHODS: Inner cell mass (ICM)/trophectoderm (TE) differentiation was performed, followed by fluorescence in-situ hybridization (FISH), to study the chromosomal distribution in both populations of cells. RESULTS: Of the 94 successfully analysed blastocysts, 68.8 +/- 1.5% of all analysable nuclei per blastocyst showed a disomic chromosomal content. Only 22.6% of blastocysts analysed were classified as normal. Of the embryos classified as abnormal at the blastocyst stage, 11.9% showed a simple mosaic pattern and 32.1% a complex mosaic pattern. An equally large group of blastocysts showed either a chaotic pattern (16.7%), or the chromosomal pattern could not be classified. The average degree of normal cells in the ICM (67.9%) was similar to the degree observed in the TE (69.5%). CONCLUSIONS: These findings indicate that chromosomally abnormal cells are not preferentially segregating to the extra-embryonic compartment of the human preimplantation embryo at the blastocyst stage. Hence, other mechanisms should be responsible for an absence of chromosomally abnormal cells in the embryo proper at later stages of development. One possible mechanism might be the elimination of the chromosomally abnormal cells by selective cell death activation.     

Developmental ability of chromosomally abnormal human embryos to develop to the blastocyst stage

BACKGROUND: A correlation between morphology, developmental competence and chromosome abnormalities is established. However, since absolute correlations are rare, embryo selection remains one of the most arduous tasks in assisted reproduction. This study was undertaken in order to determine which chromosomal abnormalities are compatible with development to the blastocyst stage. METHODS: Embryos diagnosed by preimplantation genetic diagnosis (PGD) as chromosomally abnormal or unsuitable for transfer were cultured to day 5 or 6. Morphology and development were observed daily. After extended culture, embryos were fixed and analysed by two rounds of FISH with the same probes used for PGD. RESULTS: Some types of numerical chromosome abnormalities do not preclude full differentiation in vitro. For instance, extensive mosaicism was detected in blastocysts and trisomic embryos reached the blastocyst stage with a frequency of 37%. Interestingly, only those monosomies compatible with first trimester development (monosomy X and 21) were detected at blastocyst stage. CONCLUSION: Even though there is a strong selection against chromosomally abnormal embryos, extended culture to day 5 or 6 cannot be used as a reliable tool to select against clinically relevant chromosome abnormalities such as trisomies.