Noninvasive prenatal aneuploidies testing

羊膜穿刺奪命？一滴血取代一支針 華人健康網／記者黃曼瑩／台北報導-2014年05月09日 下午18:31 高齡產婦懷孕過程可說是步步驚心，為了確認腹中胎兒是否有唐氏症的疑慮，而採取羊膜穿刺，但是，不幸的是，台中市1名老師，竟於羊膜穿刺手術檢查術後3天因細菌感染導致敗血症，母子雙亡。婦產科醫師表示，目前可以「一滴血取代一支針」的方式，避免類似細菌感染失去寶貴生命的遺憾再發生！一滴血檢測唐氏症3點注意，孕婦最好體重不要超過80公斤。1名45歲的陳小姐，因不孕症進行試管嬰兒，成功懷雙胞胎，她堅決不願意做風險高的羊膜穿刺，而改選擇一滴血篩檢胎兒染色體。婦產科醫師蔡鋒博表示，此方式稱為NIPT，只採一滴血，非侵襲性，無細菌感染的風險，準確性近百分百，可以順利檢出母血篩檢第13、18、21對染色體的情況。為了幫這1名不孕症已經11年的患者一圓生子夢，蔡鋒博醫師幫她進行子宮鏡、子宮內膜刺激術與試管嬰兒療程，因為年紀的因素，在子宮內植入4個胚胎，其中2個胚胎著床，懷孕成功。但是，因已經45歲，原以為又得面臨羊水穿刺以進行胎兒染色體檢查的壓力，所幸蔡鋒博醫師建議她使用一種安全性高的NIPT檢驗。什麼是NIPT檢驗？方式為採取孕婦靜脈血10ml，分離血漿中的DNA，利用新一代DNA定序技術進行高通量定序，進行生物資訊分析，從中即可得到胎兒的遺傳信息。NIPT檢驗方式為採取孕婦靜脈血10ml，分離血漿中的DNA，利用新一代DNA定序技術進行高通量定序。採取一滴血進行唐氏症檢驗注意事項包括：

【一滴血檢測唐氏症　3點注意】：

1.孕婦最好體重不要超過80公斤。媽媽體重太重的話，血液中胎兒DNA就會被稀釋，影響準確性。2.孕婦如果懷多胞胎要另外解釋。3.孕婦超過10週以上就可以抽血。一般建議12-18周做此檢測，主要是因若孕周較大的孕婦出現陽性結果，可能會錯過羊水穿刺或是臍血穿刺確認的最佳時間，甚至終止妊娠困難。蔡鋒博醫師表示，羊膜穿刺有千分之一到千分之三，可能出現感染、流血、流產、破水等風險，但是進行一滴血檢測唐氏症，完全沒有副作用，目前報告是可測出13、18、21對染色體的情況。但事實上，所有的染色體通通可以看的到。

Noninvasive prenatal testing for whole fetal chromosomal aneuploidies: a multicenter prospective cohort trial in Taiwan. Fetal Diagn Ther. 2014;35(1):13-7.Department of Obstetrics and Gynaecology, Chang Gung Memorial Hospital at Linkou, College of Medicine, Chang Gung University, Taoyuan, PR China.

OBJECTIVE: To evaluate the performance of noninvasive prenatal testing for all fetal chromosomal aneuploidies in an extremely high-risk group undergoing first trimester combined Down syndrome screening.

METHOD: A multicenter cohort prospective study in Taiwan was performed between June and December 2012. Maternal plasma was collected and shotgun massive parallel sequencing was performed on each fetal chromosome. 201 Taiwanese pregnant women at >12 weeks' gestation from 11 medical centers were enrolled in this trial. The extremely high-risk group was defined as a Down syndrome risk cutoff >1:30 or nuchal translucency >3.0 mm (n = 100), while the low-risk group was defined as a Down syndrome cutoff <1:1,500 (n = 101). Amniocentesis confirmation was performed and birth outcome was also recorded.

RESULTS: There were 11 cases of trisomy 21, 8 cases of trisomy 18, 3 cases of trisomy 13, 1 case of trisomy 16, 3 cases of 45,X, and 1 case of 47,XYY detected prenatally in 100 extremely high-risk gravidas [n = 27/100 (27%)]. The overall autosomal or sex chromosome aneuploidy detection rate was 96% (27/28) because of an insufficient amount maternal plasma for one fetus with Turner syndrome. In the low-risk group, no chromosomal abnormalities were detected (specificity = 100%). There were no false-positive cases in this study.

CONCLUSIONS: This first trial in Taiwan shows that noninvasive prenatal testing for whole chromosome aneuploidies can be efficiently applied in extremely high- and low-risk populations.

Noninvasive Prenatal Testing for Fetal Aneuploidy   Number 545, December 2012

The American College of Obstetricians and Gynecologists Committee on Genetics

The Society for Maternal-Fetal Medicine Publications Committee  This document reflects emerging clinical and scientific advances as of the date issued and is subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed.

ABSTRACT: Noninvasive prenatal testing that uses cell free fetal DNA from the plasma of pregnant women offers tremendous potential as a screening tool for fetal aneuploidy. Cell free fetal DNA testing should be an informed patient choice after pretest counseling and should not be part of routine prenatal laboratory assessment. Cell free fetal DNA testing should not be offered to low-risk women or women with multiple gestations because it has not been sufficiently evaluated in these groups. A negative cell free fetal DNA test result does not ensure an unaffected pregnancy. A patient with a positive test result should be referred for genetic counseling and should be offered invasive prenatal diagnosis for confirmation of test results. Noninvasive prenatal testing that uses cell free fetal DNA from the plasma of pregnant women offers tremendous potential as a screening tool for fetal aneuploidy. Circulating cell free fetal DNA, which comprises approximately 3–13% of the total cell free maternal DNA, is thought to be derived primarily from the placenta, and is cleared from the maternal blood within hours after childbirth (1). Recently, cell free fetal DNA analysis has become clinically available for women at increased risk of fetal aneuploidy. Early attempts to detect trisomic fetuses using cell free fetal DNA required the use of multiple placental DNA or RNA markers, which made the screening test time consuming and expensive (2–4). Recently, a number of groups have validated a technology known as massively parallel genomic sequencing, which uses a highly sensitive assay to quantify millions of DNA fragments in biological samples in a span of days and has been reported to accurately detect trisomy 13, trisomy 18, and trisomy 21 (5–7) as early as the 10th week of pregnancy with results available approximately 1 week after maternal sampling. Another group has described a more targeted approach, using chromosome selective sequencing to detect trisomy 18 and trisomy 21 (8). Using archived blood samples from women who were undergoing prenatal diagnosis and were at increased risk of aneuploidy, several large-scale validation studies have demonstrated detection rates for fetal trisomy 13, trisomy 18, and trisomy 21 of greater than 98% with very low false-positive rates (less than 0.5%) (6–13). Although no prospective trials of this technology are available, cell free fetal DNA appears to be the most effective screening test for aneuploidy in high-risk women. The American College of Obstetricians and Gynecologists has recommended that women, regardless of maternal age, be offered prenatal assessment for aneuploidy either by screening or invasive prenatal diagnosis regardless of maternal age; cell free fetal DNA is one option that can be used as a primary screening test in women at increased risk of aneuploidy (Box 1). This includes women aged 35 years or older, fetuses with ultrasonographic findings that indicate an increased risk of aneuploidy, women with a history of a child affected with a trisomy, or a parent carrying a balanced robertsonian translocation with increased risk of trisomy 13 or trisomy 21. It also can be used as a follow-up test for women with a positive first-trimester or second-trimester screening test result. Counseling regarding the limitations of cell free fetal DNA testing should include a discussion that the screening test provides information regarding only trisomy 21 and trisomy 18 and, in some laboratories, trisomy 13. It does not replace the precision obtained with diagnostic tests, such as chorionic villus sampling (CVS) or amniocentesis, and currently does not offer other genetic information. Other limitations of cell free fetal DNA include the lack of outcome data for low-risk populations; therefore, cell free fetal DNA testing is not currently recommended for low-risk women. Preliminary data available on twins demonstrate accuracy in a very small cohort, but more information is needed before use of this test can be recommended in multiple gestations (14). In a small percentage of cases, a cell free fetal DNA result will not be able to be obtained. To offer a cell free fetal DNA test, pretest counseling regarding these limitations is recommended. The use of a cell free fetal DNA test should be an active, informed choice and not part of routine prenatal laboratory testing. The family history should be reviewed to determine if the patient should be offered other forms of screening or prenatal diagnosis for a particular disorder. A baseline ultrasound examination may be useful to confirm viability, a singleton gestation, gestational dating, as well as to rule out obvious anomalies. Referral for genetic counseling is suggested for pregnant women with positive test results. Because false-positive test results can occur, confirmation with amniocentesis or CVS is recommended. Patients also need to be aware that a negative test result does not ensure an unaffected pregnancy; false-negative test results can occur as well. In this high-risk population, a second-trimester ultrasound examination is suggested to evaluate pregnancies for structural anomalies. In patients in whom a structural fetal anomaly is identified, invasive diagnostic testing should be offered because a cell free fetal DNA test can only detect trisomy 13, trisomy 18, and trisomy 21. Maternal serum alpha-fetoprotein screening or ultrasonographic evaluation for open fetal defects should continue to be offered.

Conclusions

l          Patients at increased risk of aneuploidy can be offered testing with cell free fetal DNA. This technology can be expected to identify approximately 98% of cases of Down syndrome with a false-positive rate of less than 0.5%.

l          Cell free fetal DNA testing should not be part of routine prenatal laboratory assessment, but should be an informed patient choice after pretest counseling.

l          Cell free fetal DNA testing should not be offered to low-risk women or women with multiple gestations because it has not been sufficiently evaluated in these groups.

l          Pretest counseling should include a review that although the cell free fetal DNA test is not a diagnostic test, it has high sensitivity and specificity. The test will only screen for the common trisomies and, at the present time, gives no other genetic information about the pregnancy.

l          A family history should be obtained before the use of this test to determine if the patient should be offered other forms of screening or prenatal diagnosis for familial genetic disease.

l          If a fetal structural anomaly is identified on ultrasound examination, invasive prenatal diagnosis should be offered.

l          A negative cell free fetal DNA test result does not ensure an unaffected pregnancy.

l          A patient with a positive test result should be referred for genetic counseling and offered invasive prenatal diagnosis for confirmation of test results.

l          Cell free fetal DNA does not replace the accuracy and diagnostic precision of prenatal diagnosis with CVS or amniocentesis, which remain an option for women.