产前检测唐氏综合症

Down syndrome is a genetic condition caused by extra copies of chromosome 21. It results in certain characteristics, including some degree of cognitive disability and other developmental delays. Common physical traits include upward slanting eyes, 鼻梁扁平的鼻梁, 手掌上只有一个褶皱(而不是通常的三个)，肌肉张力下降. Not everyone with Down syndrome has all of these traits.

The incidence of Down syndrome in the United States is about 1 in 1,000 births. There is no association between Down syndrome and culture, 少数民族, socioeconomic status or geographic region.

与年龄相关的风险

一般来说，婴儿患唐氏综合症的几率与孕妇的年龄有关. Under age 25, the odds are about 1 in 1,400. At age 35, the odds are about 1 in 350. At age 40, the odds are about 1 in 100.

原因

Down syndrome has three causes (or types):

称21三体综合症. An estimated 95% of people with Down syndrome have trisomy 21, meaning they have three number 21 chromosomes instead of two. A person normally has 23 pairs of chromosomes, each made up of genes. During fertilization of an egg by sperm, the female and male pairs of chromosomes normally split, so that only one chromosome is in each egg or sperm. 在21三体中，21对染色体不会分裂，并且会有双倍的剂量进入卵子或精子. 额外的染色体来自卵子的情况要常见得多——估计有95%到97%的几率.
易位. This causes about 3 to 4% of Down syndrome cases. In this type, an extra part of chromosome 21 gets stuck onto another chromosome. 在大约一半的情况下, 父母一方以“平衡”或隐藏的形式携带额外的21号染色体物质.
镶嵌性. 患有马赛克唐氏综合症的人在一些细胞中有额外的21号染色体，但不是所有细胞. (The unaffected cells have the usual chromosome 21 pair.) About 1 to 2% of people with Down syndrome have this type.

产前测试

筛查测试可以识别出患有唐氏综合症的婴儿风险增加的个体. There's no risk of miscarriage from being screened, but the test can't determine with certainty whether the fetus is affected. 诊断测试, 另一方面, 能准确识别胎儿的某些异常，但流产风险较小(一般小于1%)。. We offer both screening and 诊断测试.

继续阅读

筛选试验

加州所有孕妇都可以进行加州产前筛查(CA PNS)。, also called sequential integrated screening. This noninvasive process is carried out in two steps.

第一步, which is performed when the pregnancy is between 10 and 14 weeks, 从孕妇身上采集血液样本，并进行颈部半透明超声测量婴儿颈部后部的液体. If the blood test is scheduled prior to the ultrasound, we can provide those results at the end of your ultrasound appointment. 验血结果, 颈部透明度测量和孕妇年龄一起用于估计唐氏综合症和18三体(一种遗传疾病)的风险, 也被称为爱德华兹综合症, 会影响胎儿发育).

第二步是在怀孕15到20周之间对孕妇的血液样本进行测试. 当这个血液测试的结果与妊娠早期血液测试和颈部半透明超声检查的结果相结合时, the detection rate for Down syndrome increases. 该测试还提供了一个个人风险评估，胎儿患有18三体, 史密斯-莱姆利-奥皮茨综合征(一种可以减缓生长并导致智力残疾的遗传疾病), 神经管开口缺陷(胚胎神经系统形成的问题), 如脊柱裂)或腹壁缺陷(腹部的异常开口).

诊断测试

羊膜穿刺术, 绒毛膜绒毛取样(CVS)和超声是诊断测试的三个主要程序.

羊膜穿刺术我们最常用的检测方法是识别染色体问题，比如唐氏综合症吗. (在高危胎儿中, it can be used to detect other genetic diseases, 比如囊性纤维化, Tay-Sachs disease and sickle cell disease.)

用于基因检测的羊膜穿刺术通常在怀孕15至20周之间进行. 在超声引导下, 一根针穿过腹部取出一小部分羊水样本. 从液体中提取细胞进行培养，并进行核型试验——对细胞的染色体组成进行分析. It takes about two weeks to receive the results. 羊膜穿刺术 detects most chromosomal disorders with a high degree of accuracy.

There is a low risk of miscarriage as a result of amniocentesis – about 1 in 900. Miscarriage rates for amniocentesis performed at UCSF are extremely low.

羊膜穿刺术, 绒毛取样 is most commonly used to identify chromosomal problems, 比如唐氏综合症. (It can also be used to detect other genetic diseases – including cystic fibrosis, Tay-Sachs disease and sickle cell disease – in at-risk fetuses.)与羊膜穿刺术相比，CVS的主要优点是可以在怀孕早期进行, at 10 to 13 weeks rather than 15 to 20 weeks.

CVS involves removing a tiny piece of tissue from the placenta for analysis. 在超声引导下, 该样本是通过将针插入腹部或将导管插入阴道并进入子宫颈(子宫的外端)获得的。. 培养组织并进行细胞染色体组成的核型试验. It takes about two weeks to receive the results.

While it can provide information earlier in pregnancy than amniocentesis, CVS does not detect spinal cord defects. 然而, 我们可以在怀孕后期使用甲胎蛋白(AFP)血液检查或超声检查来筛查脊髓缺陷.

There is a low risk of miscarriage as a result of CVS – about 1 in 450. Miscarriage rates for CVS procedures performed at UCSF are very low.

而超声波的主要目的是确定妊娠状态-预产期, 胎儿的大小以及是否有多个婴儿——超声波也可以提供一些关于可能的出生缺陷的信息. 所有怀孕的UCSF患者在进行任何侵入性检查之前都要进行全面的超声检查. We will explain your ultrasound results at the time of your visit.

In some patients, an ultrasound raises concern for a fetal abnormality. This possibility makes ultrasound expertise crucial, 所以你可以放心，我们在执行和解释孕期超声检查方面有丰富的经验.

积极结果的意义

If you receive positive results on a screening test, 我们建议您与您的十大赌博平台排行榜和遗传咨询师讨论其影响和您的选择. They will explain what types of 诊断测试 are available. Whether to have invasive genetic testing is your decision.

If a diagnostic test finds a genetic abnormality, 我们建议与专家讨论结果的意义, including a medical geneticist and a genetic counselor, 还有你的十大赌博平台排行榜.

加州大学旧金山分校健康 medical specialists have reviewed this information. 它仅用于教育目的，并不打算取代您的十大赌博平台排行榜或其他医疗保健提供者的建议. 我们鼓励您与您的供应商讨论您可能遇到的任何问题或疑虑.