用7-AAD检测细胞DNA含量的流式细胞技术

目的：探索利用荧光染料7～AAD检测细胞DNA含量的流式细胞技术。方法：利用7一AAD和PI两种荧光染料标记小鼠胸腺T淋巴细胞通过流式细胞仪检测其G0／G1期、S期和G2／M期的DNA含量,比较2种方法测定结果。结果：通过流式细胞仪对细胞周期进行分析显示：用7一AAD和PI两种荧光染料标记的小鼠胸腺T淋巴细胞呈现完整的细胞周期,G0／G1期细胞含量为73．2％±1．93％、73．9％±1．79％,S期细胞含量为23．6％±1．04％、22．6％±1．50％,G2／M期细胞含量为3．2％±0．28％、3．5％±0.21％,两种标记方法测定结果基本一致。结论：本文探讨的7-AAD染色检测DNA含量法与常用的PI标记法相比较结论一致,且操作上更为简单快捷,是—种值得推广的DNA周期分析染色方法。     

磷脂酰肌醇-3-激酶p55γ-N末端24个氨基酸对体外培养HaCaT细胞增殖的影响

目的 观察磷脂酰肌醇-3-激酶(PI3K)的调节亚单位p55γ-N末端24个氨基酸抑制人永生化角质形成细胞系HaCaT细胞增殖的作用.方法 构建含有PI3K-p55γ-N末端24个氨基酸的腺病毒载体AD-N24-GFP及对照病毒AD-GFP,感染HaCaT细胞,流式细胞仪检测细胞周期进程,应用BrdU/PI双掺入法检测其对细胞DNA合成的影响,CFDA-SE(细胞增殖示踪荧光探针)标记法检测细胞增殖情况.结果 AD-N24能有效阻滞HaCaT细胞周期进程于G 0/G 1期,S期和G 2/M期细胞减少,AD-N24-GFP组各期细胞分布为:G 0/G 1期(84.18±1.73)%,S期(7.60±1.47)%,G 2/M期(8.22±1.33)%,而AD-GFP组各期细胞分布为:G 0/G 1期(61.14±2.76)%,S期(24.54±1.29)%,G 2/M期(14.32±1.61)%,空白对照组各期细胞分布为:G 0/G 1期(65.78±2.11)%,S期(22.22±1.92)%,G 2/M期(12.00±1.19)%,AD-N24-GFP组与AD-GFP组及空白对照组间G 0/G 1期和S期细胞比例的差异有显著性意义(P ＜0.05);BrdU阳性细胞比例显示:AD-N24-GFP组R2为:(5.89±1.33)%,AD-GFP组R2为:(27.09±2.61)%,空白对照组R2为:(24.91±2.04)%,提示AD-N24能有效抑制HaCaT细胞的DNA合成;CFDA-SE检测显示AD-N24-GFP组增殖指数(PI)为:(33.60±2.52),AD-GFP组PI为:(52.47±4.41),空白对照组PI为:(55.29±7.61),提示AD-N24能有效抑制HaCaT细胞的增殖.结论 在HaCaT细胞中过表达N24能有效阻滞HaCaT细胞周期进程,干预其细胞DNA合成,抑制其细胞增殖.     

生长激素对结肠癌肿瘤细胞体外影响

目的: 检测生长激素对体外培养的结直肠癌细胞的影响,并探讨其作用机制?方法:结肠癌细胞株Lovo细胞随机分组,加或不加不同浓度的生长激素孵育不同时间后,以MTT法检测细胞增殖情况,流式细胞术分析细胞周期,Annexin V/PI双染色法检测细胞凋亡情况?结果:MTT法测定表明,生长激素对Lovo细胞有明显的促进增殖效应,12~24 h起效,48 h时达高峰,生长激素达到一定浓度后,其促增殖作用不再增加?流式细胞仪检测生长激素对结肠癌细胞的影响显示:浓度为200 ng/ml的生长激素作用Lovo细胞24 h后,G0/G1细胞比例下降,S期细胞比例明显上升,G2/M期细胞比例稍上升,凋亡指数无明显变化(P=0.187);72 h时, G0/G1期细胞下降更为明显,S期细胞比例上升亦更为明显,G2/M期细胞上升明显,凋亡细胞比例明显增高(P < 0.01)?结论:生长激素对Lovo细胞有明显的促增殖作用,并有受体饱和效应?该作用是通过改变细胞周期分布,促进G0/G1期细胞向S期?G2/M期细胞转变实现的?     

氯硝柳胺对肾上腺皮质癌SW-13细胞增殖和凋亡的影响

目的 研究氯硝柳胺对人肾上腺皮质癌SW-13细胞株细胞增殖、细胞周期、细胞凋亡和细胞迁移力、侵袭力的影响.方法 通过体外培养SW-13细胞,采用CCK8法和iCELLigence实时无标记细胞增殖监测仪检测不同浓度氯硝柳胺对细胞增殖的影响;设对照组和氯硝柳胺组,流式细胞技术检测氯硝柳胺作用后SW-13细胞周期的变化,AO/EB染色法和Annexin V/PI染色流式细胞技术测定细胞凋亡率的变化,Transwell实验和细胞划痕实验检测细胞侵袭、迁移能力的变化,Western blot(WB)法检测β-catenin/LRP6表达的变化.结果 不同浓度的氯硝柳胺分别作用SW-13细胞24、48、72、96、120 h后,呈时间和浓度依赖性抑制SW-13细胞增殖(F=157.93,P<0.001);流式细胞仪周期检测结果显示24、48、72 h后,与对照组相比氯硝柳胺组将SW-13细胞周期阻滞在G0/G1期(P=0.001、0.005、0.008);AO/EB染色法和Annexin V/PI染色法结果均显示氯硝柳胺组的凋亡率与对照组相比明显升高(P<0.001);Transwell实验结果示氯硝柳胺组SW-13细胞的侵袭力降低(P<0.001),细胞划痕实验结果显示氯硝柳胺组SW-13细胞的迁移能力下降(P=0.002),WB结果示氯硝柳胺组SW-13细胞β-catenin/LRP6的表达明显降低(P<0.001).结论 氯硝柳胺抑制人肾上腺皮质癌SW-13细胞增殖,阻滞细胞周期,抑制侵袭及迁移能力,促进细胞凋亡;可能与其抑制Wnt/β-catenin信号通路有关.     

用DAPI和Hoechst33342染色法检测DNA的流式细胞方法探讨

目的：探索利用DAPI和Hoechst33342两种荧光染料检测DNA的流式细胞技术。方法：分别用DAPI、Hochest和PI 3种荧光染料标记HT-29细胞,通过流式细胞仪检测其G0/G1期、S期和G2/M期的DNA含量,比较3种方法测定结果。用标准荧光微球和DNA 质量控制试剂盒做测试质控。结果：质控实验显示,紫外激光的变异系数（CV）为2.4;DAPI和Hoechst33342标记的小鸡红细胞核(chicken erythrocyte nuclei,CEN)出现4个峰,第2、第3和第4峰所在道数的平均值与第1峰的比值为2、3、4,且第1峰的CV均为2.4。DAPI、Hoechst33342标记小牛胸腺细胞核（calf thymocyte nuclei ,CTN）出现2个峰,G2/G1为1.97,且G0/G1峰的CV为2.4。DAPI、Hoechst33342和PI 3种染料标记的HT-29细胞呈现完整的细胞周期峰,结果分别为CV值 3.40、3.02和4.42,G0/G1期含量为60.86%、60.22%和60.81%,S期含量为28.85%、29.70%和29.82%,G2/M期含量为10.29%、9.09%和9.37%,3种标记法测定结果一致。 结论：本文探索的DAPI和Hoechst33342标记法简单易行,可作为具备紫外激光器的流式细胞仪的首选DNA荧光染料。     

赖氨匹林对宫颈癌Hela细胞增殖及凋亡的影响

目的研究赖氨匹林(aspisol)对人宫颈癌Hela细胞增殖、凋亡和周期的影响。方法取处于对数生长期的Hela细胞,实验分为4组:阴性对照组只加等体积的低糖DMEM培养液Hela细胞;实验组加入不同浓度的aspisol,使其终浓度分别为1 mmol/L、5 mmol/L、10 mmol/L。采用描计细胞生长曲线法检测细胞增殖状态;HE染色、AO/EB方法进行凋亡细胞形态学的观察。Annexin V-FITC/PI双染检测赖氨匹林对Hela细胞作用24 h后细胞凋亡情况;流式细胞术分析赖氨匹林对Hela细胞作用24 h后细胞周期的变化。结果与对照组比较,aspisol(1,5,10 mmol/L)可呈时间、浓度依赖性抑制Hela细胞的增殖;HE染色光镜下见Aspisol组细胞密度减小,细胞变圆,胞核染色变浅。赖氨匹林(1,5,10mmol/L)作用24 h后诱导Hela细胞的早期凋亡率分别为(5.73±0.87)%、(19.11±2.86)%、(33.72±5.06)%,与对照组(0.46±0.69)%比较,差异有统计学意义(P<0.01),并呈浓度依赖性。细胞周期检测显示赖氨匹林对Hela细胞有G0/G1期阻滞作用。结论 aspisol对宫颈癌Hela细胞有抑制增殖、诱导其凋亡和改变其细胞周期分布,阻滞Hela细胞于G0/G1期。     

小儿血管瘤细胞周期分析及凋亡观察

目的探讨婴幼儿血管瘤增生和自行消退的机制.方法收集未经任何治疗的婴幼儿血管瘤手术切除标本37份(增生组24份和消退组13份).先制备单细胞悬液，运用流式细胞术对血管瘤细胞进行细胞周期参数分析，获取S、G2/M和G0/G1各期细胞比例数S％、G2/M％和G0/G1％，得到细胞增殖指数(PI)，了解细胞增殖情况.测定血管瘤细胞凋亡情况，得细胞凋亡比例数(AV ％).结果增生组和退化组的PI分别是13.49±2.08、7.85±1.78，差别有显著性意义(P＜0.01)，增生期的PI明显高于退化期.增生组和退化组的S％分别是5.99±1.85、1.92±0.65；G2／M％分别是7.46±1.82、5.94±1.63，在细胞周期中，增生组处于S期的细胞多于退化组(P＜0.01)，而处于G2/M的细胞数增生组多于退化组，但不如S期显著(P＜0.05).增生组和退化组的AV ％分别是9.84±3.05、16.18±4.89，退化组明显高于增生组(P＜0.05).结论细胞增殖、凋亡的失衡是婴幼儿血管瘤增生、消退的机制之一，凋亡在血管瘤的消退过程中发挥重要的作用.     

厌氧加强三氧化二砷对A549细胞G1期的阻滞作用

[摘要]目的观察低浓度三氧化二砷(As2O3)在不同氧环境下对肺癌A549细胞增殖抑制、细胞周期阻滞、细胞凋亡的诱导作用。方法分别在常氧(21% O2)、低氧(5% O2)、厌氧(0% O2)环境利用0 μmol/L As2O3(空白对照组)、1 μmol/L As2O3、1 μmol/L VP-16体外诱导培养肺癌A549细胞24 h,通过甲基噻唑基四唑(methyl thiazolyl tetrazolium, MTT)法测细胞增殖抑制率,通过碘化丙啶(propidium iodide, PI)染色、流式细胞仪检测细胞周期,通过Annexin Ⅴ/PI双染色法检测细胞凋亡。结果1 μmol/L As2O3组A549细胞增殖抑制率及G0/G1期细胞比例随缺氧加重而增加;厌氧环境下该组细胞增殖抑制率及G0/G1期细胞比例均高于空白对照组(P<0.05),但其细胞凋亡率较空白对照组降低(P<0.05);与3种相应氧环境下VP-16组相比较,As2O3组A549细胞增殖抑制率、G0/G1期细胞比例、G2/M期细胞比例、细胞凋亡率均减少(P<0.05)。结论1 μmol/L As2O3对A549细胞无明显诱导凋亡作用,厌氧环境下该剂量As2O3可以通过G1期阻滞抑制A549细胞增殖。     

冠心康对氧化低密度脂蛋白损伤血管内皮细胞的保护作用

目的:探讨中药复方冠心康对氧化低密度脂蛋白(oxygenized low density lipoprotei,ox-LDL)损伤的血管内皮细胞(vascular endothelial cells,VECs)的保护作用。方法:以ox-LDL损伤的人脐静脉内皮细胞作为动脉粥样硬化内皮细胞病理模型,采用冠心康药物血清干预,并与空白血清形成对照。采用MTT法检测VECs存活率,Hoechst染色、FITC/PI双染及流式细胞术检测细胞凋亡,Ki67荧光抗体标记及流式细胞术检测细胞增殖,PI染色及流式细胞术检测细胞周期。结果:与正常VECs比较,ox-LDL损伤后血管内皮细胞存活率、增殖能力及处于S期、G2/M期细胞数均明显下降(P0.05),细胞凋亡率明显升高(P0.05);经冠心康血清干预后,VECs存活率、增殖能力及处于S期、G2/M期细胞数较空白血清组、模型组升高(P0.05),细胞凋亡率降低(P0.05)。结论:中药复方冠心康能抑制ox-LDL损伤的VECs凋亡,促进细胞增殖、分裂,对ox-LDL损伤的VECs具有一定的保护作用。     

^32P照射对HL-60细胞增殖周期的影响

目的 观察^32P照射对HL-60细胞周期的影响。方法 不同剂量^32P体外照射HL-60细胞24、48和72h，流式细胞法检测细胞周期。结果 不同剂量^32P照射HL-60细胞对细胞周期有明显影响，首先发生G2/M期阻滞；随剂量增大，G2/M期和S期均发生阻滞，以G2/M期阻滞为主。结论 ^32P体外照射HL-60细胞对细胞周期有明显的干扰作用。     

Value of D-Dimers in patients with acute aortic dissection

Objective: To evaluatel the value of D-dimers in patients with acute aortic dissection (AAD). Methods: This study consisted of 16 patients with AAD and 27 non-AAD patients. Serum D-dimets were measured by Sta-Liatest D-DI immunoturbidimetric assay. Results: D-dimer level was higher (P ＜ 0.001) in patients with AAD(7.91 ± 5.52 μg/ml) than that in non- AAD group(1.57±1.24 μg/ml). D-dimer was positive (＞0.4 μg/ml) in all patients with AAD and in 10 control group patients (37%). Among patients with acute AAD, D-dimers tended to be higher in Stanford A than in Stanford B (8.67 ± 4.31 μg/ml vs. 3.24±1.27 μg/ml, P ＜0.01). D-dimer values tended to be higher in more extended disease(3.84 ± 1.65 μg/ml, 8.57 ± 3.58 μg/ml and 11.87 ± 5.69 μg/ml in thoracic aorta, thoracic and abdominal aorta, thoracic and abdominal aorta and iliacal arteries, respectively, P ＜ 0.05 for both 8.57 ± 3.58 and 11.87 ± 5.69 vs. 3.84 ± 1.65 ). Including the control group into the analysis, we found a sensitivity of 100%, a negative predictive value of 100%, and a specificity of 66% and a positive predictive value of 64% for D-dimer in diagnosis of AAD in our patients with suspected AAD. Conclusion: D-dimer was elevated in patients with AAD. A negative D-dimer test result could be useful in excluding AAD.     

Research of combined liver-kidney transplantation model in rats

Objective： To set up a simple and reliable rat model of combined liver-kidney transplantation. Methods： SD rats served as both donors and recipients. 4℃ sodium lactate Ringer＇s was infused from portal veins to donated livers,and from abdominal aorta to donated kidneys, respectively. Anastomosis of the portal vein and the inferior vena cava （IVC） inferior to the right kidney between the graft and the recipient was performed by a double cuff method, then the superior hepatic vena cava with suture. A patch of donated renal artery was anastomosed to the recipient abdominal aorta. The urethra and bile duct were reconstructed with a simple inside bracket. Results： Among 65 cases of combined liver-kidney transplantation, the success rate in the late 40 cases was 77.5%. The function of the grafted liver and kidney remained normal. Conclusion： This rat model of combined liver-kidney transplantation can be established in common laboratory conditions with high success rate and meet the needs of renal transplantation experiment.     

BLOOD PRESSURE CHANGE WITH AGE IN SALT-SENSITIVE TEENAGERS

Objective To observe blood pressure change with age in salt-sensitive teenagers whose salt sensitivity were determined by repeated testing.Methods Salt sensitivity was determined through intravenous infusion of normal saline combined with volume-depletion by oral diuretic furosemide in 55 teenagers. After five years, salt sensitivity was re-examined and subject blood pressure was followed up. Blood pressure changes in salt-sensitive teenagers were compared to that of non-salt sensitive teenagers over five years.Results After 5 years, the repetition rate of salt sensitivity determined by intravenous saline loading is 92.7%. In teenagers with salt sensitivity on the baseline, both the systolic blood pressure increments and increment rates were much higher than non-salt sensitive teenagers (12.7±12.1 mmHg vs. 2.8±5.2 mmHg, P＜ 0.01; 12.2%± 12.0% vs. 2.5% ±4.4%, P＜ 0.001,respectively). There was a similar trend for diastolic blood pressure (8.4 ± 6.4 mmHg vs. 3.7 ± 6.4 mmHg, P = 0.052; 13.2% ±10.6 % vs. 6.8%± 10.1%, P = 0.053, respectively).Conclusions Salt sensitivity determined by intravenous saline loading showed good reproducibility. Blood pressure increments with age were much higher in salt-sensitive teenagers than non-salt sensitive teenagers, especially in terms of systolic blood pressure.     

安心颗粒对急诊经皮冠状动脉介入术后生活质量影响的研究

目的：评价使用安心颗粒对急诊经皮冠状动脉介入术（PPCI）术后生活质量的影响.方法：将160例接受PPCI的急性ST段抬高型心肌梗死患者随机分为安心颗粒组（术前顿服安心颗粒8.8g,术后安心颗粒4.4 g/次,每日2次）和对照组（仅接受基础药物治疗）.所有患者均服用阿司匹林、氯吡格雷和阿托伐他汀.分别在入院时、出院前1d、出院后180 d时,应用心肌梗死多维度量表（MIDAS）、中文版SF-36评价量表对患者生活质量评分.并观察术后30 d以内的出血并发症、血小板减少症发生情况.结果：入院时和出院前1d,两组患者的心肌梗死MIDAS、SF-36量表评分比较无差异（P＞0.05）;出院后180 d时,与对照组比较,安心颗粒组MIDAS、SF-36评分明显减低（P＜0.05）;组内与入院时比较,两组出院前1d、出院后180 d时,MIDAS、SF-36评分均降低（P＜0.05）.两组患者在随访期间均无大量出血、少量出血、重度和极重度血小板减少症发生,安心颗粒组有4例、对照组有7例发生不明显出血（P＞0.05）.两组发生轻度血小板减少症的患者数比较无差异（P＞0.05）.结论：PPCI使用安心颗粒,能改善急性ST段抬高型心肌梗死患者的生活质量,且不增加出血风险.     

The comparative studies of the influences of Urapidil and Nicardipine on sino-atrial node function, atrio-ventricular node function and hemodynamics

Objective:To investigate the influences of urapidil and nicardipine on rabbit sinus function,atrio-ventricular node function and hemodynamics.Methods:Thirty-two Angora's rabbits were selected and randomly divided into four groups.U1 group:urapidil 0.25 mg/kg;U2 group:urapidil 0.5 mg/kg;N1 group:nicardipine 10 μg/kg;N2 group:nicardipine 20 μg/kg.All these medicine were administrated within 30 seconds.Measurements were taken before and after the administration of urapidil or nicardipine for the following data:mean blood pressure(MAP),heart rate(HR),sino-atrial conduction time(SACT),maximal sinoatrial recovery time(SNRTmax)corrected sinus node recovery time(CSNRT),index of sinus node recovery time(SNRTI),Wenckebach A-V conduction frequency (WB),and P-R interval.Results:Significant MAP and HR changes were identified in all of the four groups before and after administration of both urapidil and nicardipine.No significant changes could be found in the rest of the parameters.Intergroup analysis showed that SACT and CSNRT of N1 and N2 groups were shorter than those of the U2 group(P＜0.01);the MAP decreased(P＜0.01)and the HR increased drastically(P＜0.01).Conclusions:Neither urapidil(0.25 mg/kg,0.5 mg/kg)nor nicardipine(10μg/kg,20μg/kg)has any significant influence on rabbit sinus function or rabbit atrio-ventricular node function.Nicardipine could be a better choice than urapidil for parafunctional sinus node patients.     

Expression of OPGmRNA and ODFmRNA in the patients of hip fracture due to osteoporosis

Objective：To investigate the gene expression of osteoprotegerin（OPG） and osteoclast differentiation factor（ODF） in the bone tissue of patients with hip fracture due to osteoporosis. Methods：OPGmRNA and ODFmRNA in the bone tissue in 50 cases of osteoporosis sufferers（over 50 years old） with hip fracture（Observer Group） and 30 cases of hip facture sufferers with no osteoporosis（Control group） were analyzed with the Semi-Quantitative RT-PCR method. Results：The mRNA expressed of ODF, OPG were both high in the patients with hip fracture. In the control group, the expression of OPG mRNA was observed, while the expression of ODF mRNA was very slight. Conclusion：Aged patients contained all signals including OPG, ODF that are essential for inducing osteoclastogenesis and promoting bone resorption.     

The clinicopathological and immuohistochemical analysis of solid-pseudopapillary tumor of the pancreas： report of 9 cases

Objective：To investigate the clinical features, pathological characteristics and immunophenotype of solid-pseudopapillary tumor of the pancreas（SPTP）. Methods：Nine surgically treated cases of SPTP were retrospectively reviewed. Hematoxylin and Eosin（HE） staining and immunohistochemical staining were used to analyze all cases, and the general clinical data was collected. Results：Six patients were asymptomatic except for a palpable mass. Two patients complained of vague-epigastric pain. One patient appeared jaundice. The tumor was encapsulated and solid tissues alternately with cystic tissues. Histologically, the histological structure of solid portion was pseudopapillary with a fibrovascular core. Tumor cells were uniform and medium-sized which were arranged in sheets ets or nests or pseudopapillary patterns. Immunohistochemical studies demonstrated that SPTP proved positive in vimentin（9/9 cases）, AAT（9/9 cases）, NSE（9/9 cases）, ACT（7/9 cases）, CK20（2/9 cases）, CgA（1/9 cases）, S-100（3/gcases）, PR（4/gcases）, Syn（3/9 cases） and CD56（5/9cases）, negative in CEA and ER. Conclusion：SPTP is a tumor predominantly occurring in young women frequently without special symptoms. This tumor has various characteristical histological patterns with different immunophenotype.     

Dynamic Changes in Serum Estradiol and Progesterone levels in Patients of Premenstrual Syndrome with Adverse Flow of Liver-qi

Objective:To probe into the influence of changes of ovarian hormones on the pathogenesis of the specific sub-type premenstrual syndrome(PMS)and reveal partial microcosmic mechanisms of adverse flow of liver-qi.Methods:Estradiol(E2)and progesterone(P)levels in serum were determined at different phases of menstrual cycle by radioimmunoassay.Results:In the group of PMS with adverse flow of liver-qi.the secretive peak value Of E2 and P at the follicular phase significantly decreased,and the secretive peak value at the luteal phase did not come into being.Conclusions:Low E2 and P secretive peak at the follicular phase and absence of secretive peak at the luteal phase is one of the microcosmic mechanisms of PMS with adverse flow of liver-qi.One of the pathophysiologic mechanisms of specific sub-type PMS is probably the continuous low level of E2and P.     

Real-time Three-dimensional Echocardiography in Assessment of Left Ventricular and Right Ventricular Volumes

Real-time three-dimensional echocardiography (RT3DE)is a new ultrasound technique that enables dynamic threedimensional visualization and quantification of the heart in real time. Investigation of feasibility and methodology of RT3DE in determining left ventricular (LV) and right ventricular (RV) volumes, RT3DE was performed in 35 normal adults using Philips SONOS 7500 system with a 2-4 MHz matrix array transducer. The 60°×60° "pyramid" volume database was obtained and analyzed on a TomTec echo workstation. Both LV and RV volumes were calculated with four 3DE methods (i.e. apical 2, 4, 8, and 16-plane) through manually tracing ventricular endocardial borders in end diastole and end systole. Stroke volumes were then calculated. LV volume was also measured by 2DE Simpson's rule using GE VIVID 7 ultrasound machine.     

SCREENING FOR A 21-CHROMOSOME ABNORMALITY IN PREIMPLANTED EMBRYOS OF ELDERLY WOMEN

Increasing maternal age is the only etiological factor unequivocally linked to Down's syndrome in humans. The occurrence rate of newborns with Down's syndrome is about 1/220 in women over 35 years old. However, the occurrence rate in embryos fertilized in vitro, of the elder woman is unclear. Using FISH we screened the number of chromosome 21 in preimplanted embryos of 5 elderly women (average age, 38.4 years) to study the feasibility and necessity of screening trisomy 21 in embryos in patients over 35 years old at the in vitro fertilization (IVF) center.