正常人體細胞有四十六條（二十三對）染色體，每一條染色體上存在著數目不一的基因，基因是控制遺傳訊息的基本單位，人類基因的總數約為五萬至十萬個，在精卵結合時，分別帶著來自父親與母親各一半的遺傳物質。孕3月：遺傳基因診斷產前診斷胎兒異常的方法，可概略分為器官畸形的超音波診斷與遺傳基因診斷兩大類。基因遺傳性疾病正常人體細胞有四十六條（二十三對）染色體，每一條染色體上存在著數目不一的基因，基因是控制遺傳訊息的基本單位，人類基因的總數約為五萬至十萬個，在精卵結合時，分別帶著來自父親與母親各一半的遺傳物質。
某些基因產生的突變，可能會影響特定器官的形態或功能，因而導致遺傳疾病的發生，以地中海型貧血（又名海洋性貧血）為例，它是一種單基因隱性遺傳疾病，夫妻倆若為同型帶因者，每次懷孕胎兒有1/4機會完全正常，1/2機會成為帶因者，另外1/4則是重症患者。目前則可於懷孕三個月內確定重症患者的遺傳基因，才來得及提早以子宮擴刮術終止妊娠。絨毛採樣檢查 Chorionic villus sampling (CVS)
產前遺傳基因診斷必須設法得到胎兒細胞來加以分析，羊水穿刺從七十年代開始廣泛應用，基本上它是一種相當安全且準確的方法，但是，必須等到懷孕中期約十六週以後才能實施，細胞培養還要耗費二至三週的時間，等到確定胎兒異常時，往往得經由引產生下來。到了八十年代，絨毛採樣技術的發展具有下列優點：一、可於懷孕初期操作，及早確定診斷，萬一胎兒有問題，只要接受子宮擴刮術即可，減輕孕婦身心傷害。二、採得的胎兒細胞數量較多，且培養所須時間很短，適合基因分析與酵素方面的研究，對於單基因遺傳疾病，如：地中海型貧血等，是一種相當好的產前診斷方法。絨毛採樣的缺點主要是存在較高的流產率（2-5％）與感染機會（經子宮頸採樣者），此外，關於絨毛採樣可能導致胎兒畸形，特別是前幾年國內出現好幾例嚴重的肢體缺損而引起醫療糾紛，促使衛生署明令通告醫療院所，不得以絨毛採樣從事胎兒性別的鑑定。話雖如此卻也無須因噎廢食，對於特定基因遺傳疾病的產前早期診斷，一直都是優生保健工作的努力方向，事實上，只要將絨毛採樣安排於妊娠滿十週以後才做，以目前的醫學文獻中，尚未有任何造成胎兒肢體缺損的案例報告。
What is Chorionic Villus Sampling?
Chorionic Villus Sampling is another prenatal diagnostic test used to determine if a fetus has any genetic abnormalities. Like the amniocentesis, the test is done early in pregnancy, but some people prefer it to amniocentesis because it can be performed as early as 10 weeks , typically between 10 and 13 weeks (amniocentesis is done between 14-20 weeks) and the results typically come back in about 7-10 days (results for amniocentesis can take up to 4 weeks).What is the Chorionic Villi?
Chorionic villi are tiny finger-shaped growths found in the placenta. The genetic material in chorionic villus cells is the same as that in the baby’s cells so they can be analyzed and information about the baby can be obtained.Who is recommended for Chorionic Villus Sampling?
Women at an increased risk for genetic abnormalities are recommended to have prenatal diagnostic screening. Many couples choose chorionic villus sampling over amniocentesis because it can be performed earlier in the pregnancy. Additionally, if significant genetic abnormalities are found, many couples elect to terminate the pregnancy and this is easier and safer earlier in pregnancy. Indications for chorionic villus sampling are the same as for amniocentesis.How is Chorionic Villus Sampling Performed?
Chorionic villus sampling is done by
first visualizing the fetus and placenta on ultrasound. Making sure that
the fetus and placenta are not in any danger of injury, the
Obstetrician then puts a thin flexible tube (catheter) through the
vagina and cervix into the placenta and a small amount of tissue is
removed. The sample is then sent to the lab for analysis which takes
about 1 to 2 weeks. The sample can also be collected through a long,
thin needle put through the belly into the placenta.
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