产前诊断和无创检测的适用条件

本文转载自:产前筛查与遗传咨询微信公众号

本公众号受众多为患者,因此摘录的同时加了一些“自以为是”的注解,如有错误请专家指正。同时敬告各位孕妇朋友,医疗是一件很复杂的事,需要考虑方方面面,片面的理解不能代替综合诊断,因此认真听取自己医生的建议是很重要的。

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第一部分细胞遗传学产前诊断

该部分黑体字内容摘录自2010年公布的中华人民共和国卫生行业标准WS322.2-2010《胎儿常见染色体异常与开放性神经管缺陷的产前筛查与诊断技术标准第2部分:胎儿染色体异常的细胞遗传学产前诊断技术标准》;小字仅供参考。

一. 细胞遗传学产前诊断的指征:(细胞遗传学产前诊断属于有创性的产前诊断,其取材包括绒毛取材术、羊膜腔穿刺即常说的羊穿,以及经皮脐血管穿刺术,根据不同的孕周由医师选择合适的方法进行;开展最广泛、最为人熟知的就是羊穿)

1. 35岁以上的高龄孕妇;(35岁指的是预产年龄,不是做唐筛时的年龄,两者大概有半年的差距;现有的观点认为唐氏的发生风险随着孕妇的年龄升高而增加,预产年龄35岁时的唐氏发生风险已经比较高,因此规范中建议这些孕妇直接进行产前诊断,不必再做筛查)

2. 产前筛查出来的胎儿染色体异常高风险的孕妇;(也就是常说的唐筛高危人群)

3. 曾生育过染色体病患儿的孕妇;(染色体病史,是指所有的染色体异常,不仅仅指21三体、18三体等异常)

4. 产前B超检查怀疑胎儿可能有染色体异常的孕妇;(超声并不能直接看见胎儿的染色体,但是超声可以检查胎儿是否存在结构异常,其中一些为染色体病的表现;医生会根据这些表现进行适当的建议)

5. 夫妇一方为染色体异常携带者;(如果之前夫妇双方查过染色体,且有异常的话,怀孕后就不需要做产前筛查即唐筛了,需要直接做产前诊断)

6. 医师认为有必要进行产前诊断的其他情形。(比方说有家族遗传病而需要产前诊断的,虽然这时的诊断是针对遗传病的基因诊断,但是既然已经取材,可以同时进行细胞遗传学诊断;此种情况也没必要做唐筛了)

二. 介入性取材术的禁忌证:(任何检查都只能在其适用条件下进行检查,如果有风险时,就要考虑该检查是获益更大,还是风险更大;医疗有时候真的很难定出一个万全之策,这是医生和患者都不想却必须面对的;现在的无创,可以作为介入禁忌情况下的一个选择)

1. 先兆流产;

2. 术前两次测量体温(腋温)高于37.2℃;

3. 有出血倾向(血小板≤70×109/L,凝血功能检查有异常);

4. 有盆腔或宫腔感染征象;(此时穿刺可能会造成胎儿的感染)

5. 无医疗指征的胎儿性别鉴定。(不光产前诊断如此,任何医疗行为中都会禁止无医疗指征的胎儿性别鉴定)

第二部分无创产前检测,即高通量基因测序产前筛查与诊断

该部分黑体字内容来自2015年国家卫计委妇幼司委托中华医学会、全国产前诊断技术专家组研究制定的《高通量基因测序产前筛查与诊断技术规范(试行)》;小字部分仅供参考。

一.适用的目标疾病:(无创产前检测或无创DNA是我们的常用的称呼,使用的技术叫做高通量基因测序,因此该规范中将其称为高通量基因测序产前筛查与诊断,以下均同)

根据目前技术发展水平,高通量基因测序技术在产前筛查与诊断领域适用的目标疾病为常见胎儿染色体非整倍体异常(即21三体综合征、18三体综合征、13三体综合征)。(该规范为2015年发布,当时无创产前检测针对21三体、18三体、13三体的研究较多,证据充足,因此目标疾病只纳入了该三种疾病;随着研究的深入,病例的累积,我相信无创可以拓展到筛查全部的染色体数目异常、微缺失微重复,甚至单基因病的筛查;今年贝瑞和康公司就推出了一款无创的升级产品,在上面三种疾病的基础上增加了性染色体和7种常见的微缺失,不过价格也比一般的无创贵;当然,所有的无创高风险孕妇均需进行产前诊断进行确诊,必须的。)

二.适用人群

1. 血清学筛查、影像学检查显示为常见染色体非整倍体临界风险(即1/1000≤唐氏综合征风险值<1/270,1/1000≤18三体综合征风险值<1/350)的孕妇。(该规范第一次定义了临界风险;但是此处对于影像学检查何种情况适用于无创并没有描述。超声检查中,有一些指标提示染色体异常风险轻度增高,一般称为软指标,常见的有心内强回声点、轻度侧脑室扩张、轻度肾盂扩张、脉络丛囊肿等,单个存在时多不是介入性诊断的指征,许多医生认为对于此类人群可以通过无创检测进行常见染色体异常的排查)

2. 有介入性产前诊断禁忌证(先兆流产、发热、有出血倾向、感染未愈等)。(此种情况下进行介入性诊断容易造成严重的后果,如此则得不偿失;因此无创成为较好的选择)

3. 就诊时,患者为孕20+6周以上,错过血清学最佳时间,或错过常规产前诊断时机,但要求降低21三体综合征、18三体综合征、13三体综合征风险的孕妇。(从技术来说,出生之前均可以做无创,不存在孕周过大的问题;孕周太大做无创的麻烦在于,无创高风险不好进行后续的诊断或处理)

三.慎用人群

有以下几种情形的孕妇属于慎用人群,即在该人群中本检测的筛查效果较适用于人群有一定程度的下降,即筛查的检出率下降,假阳性及假阴性率可能上升,或已符合介入性产前诊断的指征,知情后拒绝直接选择介入性产前诊断的孕妇。包括:

1. 产前筛查高风险,预产年龄≥35岁的高龄孕妇,以及有其他直接产前诊断指征的孕妇。(一句话就是,已符合第一部分产前诊断指征的,都不推荐做无创)

2. 孕周<12周的孕妇。(无创的原理是检测游离在孕妇外周血中的胎儿DNA片段,12周以前胎儿DNA片段低,容易检测失败)

3.高体重(体重>100千克)的孕妇。(高体重的孕妇血容量也高,容易将胎儿DNA稀释,从而导致浓度过低检测失败)

4.通过体外受精-胚胎移植(IVF-ET)方式受孕的孕妇。(此种情况类似双胎,因为不管后面存活的是双胎还是单胎,一开始移植时都是移植了两个胚胎;现在有公司可以接收此类标本,可以具体咨询)

5.双胎妊娠的孕妇。(主要是有两种胎儿DNA,增加检测难度,而且,如果检测出异常,并不知道是哪个胚胎的的异常;现在有公司接收此类标本,可以具体咨询)

6.合并恶性肿瘤的孕妇。(无创的原理是检测游离在孕妇外周血中的胎儿DNA片段,恶性肿瘤的DNA一般发生了变异,因此恶性肿瘤DNA片段不同于孕妇本身的DNA片段,进入外周血内干扰无创的检测,容易导致结果假阳性)

四.不适用人群

1.染色体异常胎儿分娩史,夫妇一方有明确染色体异常的孕妇。(这些都是要直接进行产前诊断染色体核型分析的,必须的。无创能检测的目标疾病过少,容易漏诊)

2.孕妇1年内接受过异体输血、移植手术、细胞治疗或接受过免疫治疗等对高通量基因测序产前筛查与诊断结果将造成干扰的。(无创的原理是检测游离在孕妇外周血中的胎儿DNA片段,输血、移植等会导致异体细胞的DNA进入孕妇外周血,从而干扰无创的检测。但是我觉得,随着技术进步,这些问题有可能解决掉;有公司的资料显示,接受过免疫治疗的孕妇,距最后一次治疗4周以上的样品,同样可以做无创)

3.胎儿影像学检查怀疑胎儿有微缺失微重复综合征或其他染色体异常可能的。(同第1条,无创检测的目标疾病比较少,容易漏诊)

4.各种基因病的高风险人群。(无创在现阶段并不能检查基因病;因此需要进行有创的产前诊断,一次取材可以同时进行基因诊断和细胞遗传学诊断,就不用做无创和唐筛了)

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