强迫症与活性氧自由基的关系研究

目的：探讨脂质过氧化和氧自由基酶活性变化在强迫症病理机制中的作用。方法：测定30例强迫症患者和30例正常对照血中SOD,GSH－PX活性,GSH含量和血清中LPO含量。结果：强迫症组LPO含量,SOD活性明显高于正常对照组,GSH含量则显著降低（P＜0．05）,强迫症组SOD,GSH－PX与LPO,SOD与GSH－PX均呈显著直线正相关（P＜0．05－0．01）,正常对照组GSH－PX与HPO呈显著直线正相关。多元逐步回归分析显示强迫症组LPO与SOD含量的改变具有相关性（P＜0．01）;对照组LPO含量变化则与GSH－PX相关（P＜0．01）。结论：提示强迫症患者体内存在自由基代谢异常。     

消疲方对疲劳大鼠自由基代谢及睾酮、皮质酮的影响

目的 探讨消疲方的抗疲劳机制.方法 选用SD雄性大鼠,分为对照组、模型组和中药组,每组11只.采用21天力竭游泳方式制作运动性疲劳模型.中药组采用常规剂量灌胃给药,每日1次,共21天.采用硫代巴比妥酸法测定丙二醛(MDA);采用比色法测定谷胱甘肽(GSH)和谷胱甘肽过氧化物酶(GSH-PX);采用黄嘌呤氧化酶法测定超氧化物歧化酶(SOD);采用ELISA方法测定睾酮(T)和皮质酮(C).观察末次运动24h后大鼠睾丸、肝脏和血清MDA和GSH含量、GSH-PX和SOD活性,以及血清T和C浓度的变化,并计算T/C.结果 (1)模型组与对照组相比:模型组血清MDA显著升高(P＜0.05),而睾丸、肝脏MDA与对照组比较无显著性差异(P＞0.05);睾丸、肝脏和血清GSH和GSH-PX均显著降低(P＜0.01,0.01,0.01);肝脏SOD显著降低(P＜0.05),而睾丸、血清SOD与对照组比较无显著性差异(P＞0.05);模型组血清T、C明显升高(P＜0.01,0.01),T/C明显降低(P＜0.05).(2)中药组与模型组相比:中药组睾丸MDA明显降低(P＜0.05),而肝脏、血清MDA与模型组比较无显著性差异(P＞0.05);肝脏、睾丸和血清GSH均显著增高(P＜0.05,0.01,0.01);肝脏、睾丸GSH-PX显著增高(P＜0.01,0.01),而血清GSH-PX与模型组比较无显著性差异(P＞0.05);肝脏SOD显著增高(P＜0.05),而睾丸和血清SOD与模型组比较无显著性差异(P＞0.05);中药组血清C明显降低(P＜0.01),T/C明显升高(P＜0.05),而T与模型组比较无显著性差异(P＞0.05).结论 消疲方可以通过增强机体的抗自由基氧化酶活性、提高T/C比值,发挥抗疲劳作用.     

慢性心肌缺血小型猪的氧化应激反应指标观测

目的 观测慢性心肌缺血小型猪的氧化应激反应指标.方法 15只巴马小型猪随机分成3组,即正常对照(Ctr)组,高脂(HF)组和慢性心肌缺血(CMI)组,每组5只.采用维生素D3和异丙肾上腺素复合高脂饮食建立慢性心肌缺血模型,连续24周.造模24周后,观察各组血清CK-MB、血小板聚集率及心肌组织中SOD、MDA、GSH-Px、NO、LD和ATP酶含量的变化.结果 与Ctr组比,CMI组血清CK-MB活性、PAR、心肌组织中MDA和LD含量均显著升高(P＜0.05,P＜0.01),心肌组织中SOD、SOD/MDA比值、GSH-Px、NO、Na+-K+-ATP、Ca++-ATP和Mg++-ATP酶活性均明显降低(P0.05,P＜0.01),而HAR组PAR和心肌组织中SOD/MDA比值、MDA含量均升高显著(P＜0.05,P＜0.01),心肌组织中SOD、GSH-Px、Na+-K+-ATP、Mg++-ATP酶活性均降低显著(P＜0.05);与HF组比,CMI组血清CK-MB活性明显高于HF组(P＜0.01),心肌组织中Na+-K+-ATP酶和Ca++-ATP活性显著低于HF组(P＜0.05,P＜0.01);相关分析显示,CMI组CK-MB活性与PAR和MDA含量呈显著正相关(P＜0.05,P＜0.01),与SOD、SOD/MDA、GSH-Px、NO呈显著负相关(P＜0.05,P＜0.01);血小板聚集率与CK-MB和MDA呈显著正相关(P＜0.05),与SOD、SOD/MDA和Na+-K+-ATP酶活性呈显著负相关(P＜0.05,P＜0.01);心肌组织中LD含量与MDA呈显著正相关(P＜0.05),与SOD/MDA、Na+-K+-ATP、Ca++-ATP和Mg++-ATP呈显著负相关(P＜0.05);心肌组织中NO水平与SOD、SOD/MDA、GSH-Px呈显著正相关(P＜0.05,P＜0.01),与CK-MB和MDA呈显著负相关(P＜0.05).结论 氧化应激反应参与了慢性心肌缺血的形成过程.     

EFFECTS OF TRADITIONAL CHINESE MEDICINE HSWY ON ANTI-OXIDATIVE ABILITY OF SENILE

目的:观察何首乌饮对亚急性衰老大鼠血清丙二醛(MDA)含量、谷胱甘肽过氧化物酶(GSH-Px)和超氧化物歧化酶(SOD)活性以及总抗氧化能力(T-AOC)的影响.方法:30只雄性SD大鼠随机分为正常对照组、模型组和何首乌饮预防组,每组10只.D-半乳糖连续腹腔注射建立亚急性衰老大鼠模型,何首乌饮预防组大鼠在腹腔注射D-半乳糖的同时灌胃何首乌饮(0.06ml/kg),用药60d.分别检测各组大鼠血清MDA含量、GSH -Px活性、SOD活性及T-AOC.结果:与正常对照组大鼠比较,模型组大鼠MDA含量明显升高,GSH -Px活性、SOD活性、T-AOC明显降低(P＜0.01,P＜0.05);与模型组比较,何首乌饮预防组大鼠MDA含量明显降低,GSH -Px活性、SOD活性、T-AOC明显升高(P＜0.01).结论:何首乌饮可抑制衰老大鼠抗氧化能力的降低,具有一定延缓衰老的作用.     

脂肝泰胶囊对高脂血症性脂肪肝大鼠血清和肝组织GSH含量及GSH-PΧ活性的影响

目的探讨脂肝泰胶囊治疗高脂血症性脂肪肝的作用机制.方法采用高脂饮食喂饲大鼠复制脂肪肝模型,实验分为模型组、脂肝泰高剂量组、脂肝泰低剂量组、东宝肝泰对照组和正常对照组.以高、低剂量脂肝泰和东宝肝泰进行干预后测定各组大鼠血清、肝组织中谷胱甘肽(GSH)的含量和谷胱甘肽过氧化物酶(GSH-PΧ)的活性.结果各组大鼠血清及肝组织中GSH的含量间差别均有显著性意义(P＜0.05);除正常与脂低组、正常与脂高组、脂低与脂高组的比较外,其他各组间的两两比较,血清及肝组织中GSH的含量间差别均有显著性意义(P＜0.05).各组大鼠血清及肝组织中GSH-PX的活性间差别均有显著性意义(P＜0.01);除正常与脂高组外,其他各组间的两两比较,血清及肝组织中GSH-PX的活性间差别均有显著性意义(P＜0.01).结论脂肝泰胶囊可提高大鼠血清、肝组织中GSH的含量和GSH-PΧ的活性,提高机体抗氧化能力.     

曲美他嗪对大鼠缺血再灌注心肌线粒体的保护作用

目的探讨曲美他嗪(trimetazidine,TMZ)对缺血再灌注损伤(RI)心肌线粒体的保护作用及其机制.方法50只雄性SD大鼠随机分为假手术组、等渗盐水组和药物组(TMZ 5 mg/kg组及TMZ 10 mg/kg组)共四组,假手术组只剖胸,不结扎冠状动脉.余三组制作RI模型,缺血前分别静脉注射TMZ(5 mg/kg或10 mg/kg)或等量等渗盐水,在缺血30 min及再灌注40 min时测定RI区心肌线粒体丙二醛(MDA)、超氧化物歧化酶(SOD)、谷胱甘肽(GSH)、谷胱甘肽过氧化物酶(GSH-PX)及总钙浓度,并通过电镜观察心肌超微结构改变.结果与假手术组相比,等渗盐水组及药物组线粒体中的MDA及总钙显著增高(P＜0.01),SOD、GSH及GSH-PX显著降低(均P＜0.01);与等渗盐水组比较,药物组的MDA及总钙水平显著降低(P＜0.05,P＜0.01),SOD、GSH及GSH-PX显著增高(P＜0.05,P＜0.01).结论TMZ能减轻缺血再灌注心肌线粒体的脂质过氧化损伤,其机制可能是通过提高线粒体内GSH含量及SOD、GSH-PX活性,增强其抗氧化能力,并通过减轻线粒体内钙聚积在细胞水平提供心肌保护作用.     

何首乌水提液对老化模型大鼠脑组织内抗氧化酶表达的影响

目的 观察何首乌水提液对老化模型大鼠海马、皮质超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-PX)和丙二醛(MDA)含量的影响.方法 采用氟派啶醇致大鼠获得性老化动物模型,用盐酸丁咔地尔腹腔注射作阳性对照,测定空白对照组、模型组、阳性对照组、何首乌大、小剂量组海马和皮质SOD、GSH-PX和MDA含量.结果 模型组SOD、GSH-PXH量较空白对照组均显著降低(P＜0.01),MDA含量均显著升高(P＜0.01);与阳性对照组比较,何首乌大、小剂量组可显著提高大鼠海马、皮质SOD、GSH-PX含量(P＜0.01),同时何首乌大剂量组MDA含量较阳性对照组显著降低(P＜0.01),何首乌小剂量组MDA含量较阳性对照组明显升高(P＜0.05).结论 何首乌是通过上调抗氧化酶SOD和GSH-PX、下调过氧化物MDA表达起到延缓衰老的作用.     

硒对小鼠抗氧化作用的研究

目的:研究并比较有机硒和无机硒对小鼠GSH-PX活性、SOD活性以及LPO含量的影响.方法:先制备硒蛋白,然后把小鼠分成四组,第一组给硒蛋白,第二组给硒多糖,第三组给亚硒酸钠,第四组给蒸馏水.饲喂3周分别测定各小组小鼠GSH-Px 活性、肝SOD活性和脑、心肌LPO含量.结果:有机硒能显著增强GSH-PX活性,又能提高SOD活性,可有效防止血液中LPO的产生,并且表现出剂量与抑制作用成正相关.硒蛋白与硒多糖相比生物效应更为显著(P<0.01),亚硒酸钠只能提高GSH-PX活性(P<0.05),对肝SOD活性影响极不显著(P>0.05).三种硒对3月龄鼠脑、心肌LPO含量均无影响,但能降低12月龄鼠脑、心肌LPO含量,有机硒的效应远远超过无机硒,12月龄鼠脑、心肌LPO含量几乎接近3月龄鼠.结论:硒蛋白抗衰老、抗氧化和抗疾病等能力最强.硒蛋白中的硒比硒多糖和亚硒酸钠中的硒对GSH-PX的活性更为重要.     

骨肿瘤患者LPO,SOD与GSH-PX变化的研究

对72例骨肿瘤,30例非瘤骨疾病患者血清脂质过氧化物(LPO)含量和全血超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-PX)活性的测定,并与60例正常对照组比较、显示LPO在非瘤骨病组、良性骨肿瘤、恶性骨肿瘤组呈逐渐增高趋势(P<0.05)。SOD活性在骨肿瘤组明显低于对照组与非瘤骨病组(P<0.05～0.01),恶性骨肿瘤又低于良性骨肿瘤组(P<0.01)。作者认为在恶性骨肿瘤患者测定SOD活性和SOD/LPO比值有一定的临床参考价值。     

糖尿病视网膜病变患者血清同型半胱氨酸与氧化应激反应的变化

目的 观察糖尿病视网膜病变(DR)患者血清同型半胱氨酸与氧化应激反应的变化,探讨糖尿病视网膜病变患者血清同型半胱氨酸水平与氧化应激反应的相关性.方法 测定50例健康对照者,50例无DR 2型糖尿病患者(NDR组)、50例合并非增殖型DR 2型糖尿病患者(NPDR组)及50例合并增殖型DR 2型糖尿病患者(PDR组)血清同型半胱氨酸(Hcy)及丙二醛(MDA)、超氧化物歧化酶(SOD)、还原型谷胱甘肽(GSH)水平.结果 所有糖尿病患者Hcy、MDA含量均明显高于正常对照组(P＜0.01);NPDR组及PDR组均较NDR组明显升高,血清SOD、GSH含量所有糖尿病患者低于正常对照组(P＜0.01);NPDR组及PDR组均较NDR组低(P＜0.01);同时PDR组又低于NPDR组(P＜0.01);血清Hcy与MDA水平呈正相关(r=0.84,P＜0.05),与SOD、GSH含量均呈负相关(r=-0.77,-0.68,P＜0.05).结论 糖尿病视网膜病变患者血清同型半胱氨酸水平升高,氧化应激反应增强,氧化应激与血清同型半胱氨酸水平升高有关,血清同型半胱氨酸水平升高,氧化应激在糖尿病视网膜病变发生发展中发挥重要作用.     

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.