（請翻譯，預計交稿日8/27）唐氏症染色體有幾條？懷孕照超音波會有哪些特徵？How Many Chromosomes Are in Down Syndrome? What Ultrasound Signs Can Be Seen During Pregnancy?

唐氏症（Down syndrome），又稱蒙古症（mongolism），是一種先天性疾病，會導致行為障礙、肢體發育異常以及其他器官的異常，同時伴隨輕至中度的智能障礙。

該疾病在出生時就會出現症狀，目前尚無醫療方法能完全治癒。
Down syndrome, also called mongolism, is a congenital condition that can lead to behavioral challenges, physical developmental differences, and abnormalities in other organs, often accompanied by mild to moderate intellectual disability. Symptoms are present from birth, and there is currently no treatment that can fully cure the condition.

大多數唐氏症患者在外貌特徵、發育過程、易發疾病、智力狀況及壽命方面具有相似性。和其他先天性疾病相比，唐氏症是最早被發現並且研究最為深入的染色體疾病之一。
Most individuals with Down syndrome share similarities in physical features, developmental patterns, susceptibility to certain illnesses, cognitive abilities, and life expectancy. Compared with other congenital conditions, Down syndrome is one of the earliest chromosomal disorders to be identified and also one of the most thoroughly studied.
 

在台灣，約有92%的唐氏症患者是由第21對染色體異常所引起；4%為染色體轉位所致；另有4%屬於細胞鑲嵌型唐氏症。
In Taiwan, about 92% of Down syndrome cases are caused by abnormalities in the 21st pair of chromosomes, 4% result from chromosomal translocation, and another 4% are classified as mosaic Down syndrome.
 

唐氏症染色體有幾條？How many chromosomes are there in Down syndrome?

唐氏症屬於最常見的染色體異常症，是因為人體的第21對染色體異常所造成，發生唐氏症機率大約為1/800，即每800位新生兒就有一位是唐氏症寶寶。Down syndrome is the most common chromosomal disorder, caused by an abnormality in the 21st pair of chromosomes. The chance of having a baby with Down syndrome is about 1 in 800, meaning that approximately one out of every 800 newborns is affected.

為什麼寶寶會有唐氏症？Why does a baby develop Down syndrome?

在正常情況下，人體的染色體是成雙成對存在的，總共有23對、46條染色體。

然而，如果父母的生殖細胞在形成過程中發生分離異常，導致精子或卵子中多出一條染色體，第21對染色體異常（多出一條），則會干擾遺傳基因的功能，因此形成了臨床上異常的症狀。

醫學研究指出，造成21對染色體異常的原因主要是卵子老化，使細胞在進行減數分裂時，沒有正常分裂，導致受精後，在23對染色體中的第21對多出一條（正常為兩條）。

因為唐氏症染色體異常的原因和卵子老化有關，故媽媽的年紀是其中一個重要因素，據統計高齡產婦 懷上唐氏症機率較高。
Under normal circumstances, human chromosomes exist in pairs — a total of 23 pairs, or 46 chromosomes.
However, if an error occurs during the formation of reproductive cells, causing the sperm or egg to carry an extra chromosome, the 21st pair will end up with an additional copy. This disrupts the function of genetic material and leads to the clinical symptoms seen in Down syndrome.

Medical studies have shown that the main reason for abnormalities in the 21st pair is the aging of the egg. As eggs get older, errors in meiotic division become more likely, and instead of having the usual two chromosomes in the 21st pair, the fertilized egg ends up with three.

Because this chromosomal abnormality is closely related to egg aging, a mother’s age is considered an important factor. Statistics show that the likelihood of having a baby with Down syndrome is higher among older mothers.
 

3種唐氏症染色體變異的類型 Three Types of Chromosomal Variations in Down Syndrome

1. 三染色體症（trisomy 21）：染色體無分離（nondisjunction）
2. 轉位型：染色體轉位 （translocation）
3. 鑲嵌型：異常細胞鑲嵌 （mosaicism）（體內有正常跟異常的2種細胞）
   
   
   Trisomy 21: caused by chromosomal nondisjunction
   Translocation: caused by chromosomal translocation
   Mosaicism: a mixture of normal and abnormal cells in the body
    

其中三染色體症（trisomy 21）屬於最常見的，約佔比唐氏症染色體變異類型的95%。Among these, Trisomy 21 is the most common, accounting for about 95% of all Down syndrome cases.

懷孕照超音波會發現嗎？Can Down syndrome be detected through pregnancy ultrasounds?

唐氏症寶寶的症狀，可以在懷孕初期從胎兒的頸部透明帶中進行觀察。

頸部透明帶指的是胎兒頸部後方皮下積液形成的透明空隙，在超音波影像中呈現帶狀。

一般而言，正常胎兒的頸部透明帶厚度多在2.5至3毫米以下；若透明帶較厚，則可能與染色體異常（如唐氏症）相關，因此醫師會以此作為早期篩檢的重要指標之一，用以評估胎兒罹患唐氏症的機率。

在進行孕期超音波時，除了觀測胎兒的頸部透明帶會比較厚之外，罹患唐氏症的胎兒的鼻梁骨也會比較短，或沒有鼻梁骨。

然而鼻梁骨的長短只能作為唐氏症的可能症狀，並不能視同確診唐氏症，因為胎兒的鼻梁骨長短亦有可能來自遺傳父母的長相。

In early pregnancy, one of the first signs doctors look at is the nuchal translucency (NT) — a fluid-filled space at the back of the baby’s neck that appears as a clear band on the ultrasound.

Typically, the nuchal translucency in healthy fetuses measures less than 2.5 to 3 millimeters. A thicker NT may be associated with chromosomal abnormalities, such as Down syndrome, which is why it is considered an important marker for early screening.

During ultrasound examinations, doctors may also observe other features. For example, babies with Down syndrome may have a shorter nasal bone, or in some cases, the nasal bone may be absent.

However, the length of the nasal bone alone cannot confirm Down syndrome, as nasal bone size can also be influenced by parental genetics. It is only one possible indicator and should be assessed together with other screening results.
 

唐氏症寶寶有什麼特徵？What are the features of a baby with Down syndrome?

唐氏症患者的心智與生理發展通常較同齡人緩慢。雖然部分唐氏症新生兒在出生時的體重與身長可能接近平均值，但隨著成長，發育速度及能力會逐漸落後於同齡兒童。

患有唐氏症的人往往具有一系列相似且明顯的生理特徵，例如：頸部較短、耳朵形狀略異常、舌頭相對突出、頭型偏小、臉部輪廓較扁平、眼睛虹膜上可能出現白色斑點、手指較短、掌紋較深。

由於四肢發育較短小，他們的肌肉張力普遍偏低，部分患者的舌頭與韌帶也較鬆弛，可能出現下垂的情況。

唐氏症寶寶通常也容易併發一些生理疾病，包含：聽力問題、先天性心臟疾病、腸道短小阻塞、腹腔疾病、白內障、甲狀腺功能異常、骨骼發育異常、阿茲海默症，以及免疫系統異常，較容易罹患肺炎等感染病。

此外，唐氏症寶寶也可能較容易罹患智能及社交情緒等心理疾病，部份唐氏症寶寶的個性較為固執、注意力不集中、有強迫行為、憂慮傾向等。

Children with Down syndrome generally develop more slowly, both mentally and physically, compared to other children of the same age. While some newborns with Down syndrome may have an average weight and length at birth, their growth and developmental milestones often lag behind as they grow older.

They tend to share a range of distinctive physical features, such as a shorter neck, slightly unusual ear shape, a tongue that protrudes, a smaller head size, a flatter facial profile, white spots on the iris, shorter fingers, and a single deep crease across the palm.

Because their arms and legs are usually shorter, many also have lower muscle tone. Some may experience looseness in the tongue and ligaments, leading to a drooping appearance.

Babies with Down syndrome are also more prone to certain health conditions, including hearing problems, congenital heart disease, intestinal blockages, abdominal issues, cataracts, thyroid disorders, skeletal abnormalities, Alzheimer’s disease, and immune system problems that make them more vulnerable to infections like pneumonia.

In addition, they may be at higher risk of developmental and emotional challenges. Some children with Down syndrome may show traits such as stubbornness, short attention span, compulsive behaviors, or a tendency toward anxiety.
 

唐氏症機率高嗎？下一胎也會是唐氏症嗎？Is the risk of Down syndrome high? Will my next baby also have Down syndrome?

每一位孕婦都有可能生出唐氏症寶寶，且隨著孕婦年齡的增加，生出唐氏症機率會隨著孕婦年齡增加而提升。

根據統計，20歲孕婦生下唐氏症寶寶的機率約為1/1528，30歲時約為1/909，而年滿34歲以上的孕產婦這個風險進一步增加到約1/270。

因應這個風險，台灣衛生福利部建議滿34歲以上的孕婦在孕期篩檢時，可以直接選擇接受羊膜穿刺檢查，透過抽取羊水進行染色體分析，這種檢查方式更為精準且能提供確診的依據。

對於34歲以下的孕婦，雖然個別風險較低，但由於這個年齡群的孕婦在整體孕產婦中佔比更高。

且約80%的唐氏症寶寶是由34歲以下孕婦所生，因此醫學界也強烈建議34歲以下的孕婦應接受唐氏症的孕期篩檢，以早期發現風險並做後續的評估與決策。

簡而言之，不論年齡大小，每位孕婦都有生出唐氏症寶寶的可能性，因此，孕期篩檢和適當的診斷檢查對於保障母嬰健康非常重要。

Every expectant mother has a chance of giving birth to a baby with Down syndrome, and the risk increases with maternal age.
Statistics show that at age 20, the chance is about 1 in 1,528; at age 30, it rises to 1 in 909; and for mothers aged 34 and above, the risk further increases to around 1 in 270.

Because of this, Taiwan’s Ministry of Health and Welfare recommends that women aged 34 or older consider amniocentesis as part of prenatal screening. This test analyzes chromosomes from amniotic fluid and provides more accurate, diagnostic results.

For women under 34, the individual risk is lower, but since this age group makes up the majority of pregnant women, about 80% of babies with Down syndrome are actually born to mothers under 34. For this reason, medical experts also strongly advise prenatal screening for younger mothers, so that any potential risks can be identified early and appropriate follow-up decisions can be made.

In short, regardless of age, every pregnant woman has some risk of having a baby with Down syndrome. That’s why prenatal screening and proper diagnostic testing are so important for protecting both mother and baby’s health.
 

有什麼方法可以預防生出唐氏症寶寶嗎？Is there a way to prevent having a baby with Down syndrome?

目前，醫療上主要透過孕前健檢 與診斷來降低生育唐氏症寶寶的風險。

根據統計，台灣約每800位新生兒中就有 1 位為唐氏症患者。唐氏症染色體異常無法透過疫苗預防，也沒有藥物或醫療治療可以根治，因此孕期篩檢是唯一的預防方式。
Currently, the main medical approach to lowering the risk is through pre-pregnancy health checks and prenatal diagnostic tests.

Statistics show that in Taiwan, about 1 in every 800 newborns is born with Down syndrome. Since chromosomal abnormalities in Down syndrome cannot be prevented with vaccines, and there is no medicine or treatment that can cure it, prenatal screening remains the only effective way to detect and reduce the risk early on.
 

常見的孕期檢測方法 Common Prenatal Screening Methods

• 第一孕期與第二孕期的唐氏症篩檢
  First- and second-trimester Down syndrome screenings
• 非侵入性胎兒染色體篩檢（NIPT）
  Non-invasive prenatal testing (NIPT)
• 羊膜穿刺：抽取約10 c.c.的羊水檢測胎兒染色體，可搭配羊水晶片分析，以判斷染色體是否存在小片段缺失或其他異常
  Amniocentesis: about 10 c.c. of amniotic fluid is collected to examine the baby’s chromosomes. This can be combined with microarray analysis to detect small chromosomal deletions or other abnormalities.

這些檢查能在孕期提早評估，並確定胎兒是否患有唐氏症或有其他染色體異常狀況。These tests allow doctors to evaluate risks early in pregnancy and determine whether the baby has Down syndrome or other chromosomal conditions.

雖然唐氏症尚無法以藥物根治，但隨著研究與醫療資源的進步，早期療育已成為重要的介入方式。Although there is currently no medication to cure Down syndrome, advances in research and medical care have made early intervention and therapy an important part of treatment.

例如：唐氏症寶寶常見的症狀是肌肉張力不足，透過早療課程中的肌力與動作訓練，可促進其肌耐力發展，並培養生活自理能力。長期介入可幫助患者在成長過程中提升獨立生活的可能性。
For example, babies with Down syndrome often have low muscle tone. Through early intervention programs such as strength and movement training, they can improve muscle endurance and gradually develop self-care skills. With long-term support, these therapies help increase their ability to live more independently as they grow.

參考資料 Reference：https://www.cmuh.cmu.edu.tw/HealthEdus/Detail?no=5256