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When noninvasive prenatal testing (NIPT) first became a reality nearly a decade ago, many involved in the care of pregnant women (clinicians and laboratorians alike) saw it as a game-changer. They thought the standard screening option for chromosomal abnormalities, maternal serum screening (MSS), would soon be obsolete. NIPT is a powerful test for Down syndrome and certain other chromosomal abnormalities with a high positive predictive value (PPV). This means there is a significantly lower false-positive rate, so it is likely that a positive result means the fetus actually has the condition. For example, QNatal® Advanced, Quest Diagnostic’s NIPT test, has an overall positive predictive value (PPV) for Down syndrome of 98.1%, with a false positive rate (FPR) of only 0.1%1. Compare that to the Quad screen or First Trimester screening, which have a PPV of less than 3% and an FPR of 5% for Down syndrome. Thus, NIPT can result in a significant decrease in the number of invasive prenatal diagnostic procedures (amniocentesis or chorionic villus sampling ) with a resulting reduction in procedural-related fetal losses. But this is not necessarily the end of the story.


What information can MSS provide?


MSS is a measurement of certain chemicals in a pregnant mom’s blood to assess a baby’s risk for Down syndrome and trisomy 18. It has been used to screen for open neural tube defects (ONTD) since the 1970s, Down syndrome since the 1980s, and trisomy 18, since the 1990s. In addition to Down syndrome and trisomy 18, other atypical chromosome abnormalities may be serendipitously ascertained with a screen positive MSS. For example, a woman with a screen positive for Down syndrome or trisomy 18 may have a fetus with a different, less common chromosome abnormality. In fact, one study found that abnormal first trimester screens identified 55% of such unusual chromosome abnormalities2. Some physicians use the MSS biochemical levels to independently screen for pregnancies at risk for complications such as pre-eclampsia, low birth weight, preterm delivery, or fetal demise. AFP (alpha fetoprotein) is measured as part of MSS and is a key predictor of spina bifida, regardless of concern for chromosome abnormalities.


What information can NIPT provide?


NIPT is also a blood test, looking at DNA from the placenta to assess a fetus’s risk for certain chromosome abnormalities. Some providers routinely offer NIPT, and if the results are abnormal, follow-up diagnostic testing is offered. It is important to counsel patients that NIPT will not identify all chromosome abnormalities. This is especially significant for younger women (less than 36 years of age) as they have a higher risk for these less common chromosome abnormalities than for Down syndrome3. ACOG recently recommended that NIPT should be offered to pregnant patients regardless of age3. MSAFP for ONTD’s should be ordered in the second trimester, as NIPT does not screen for these.


Some providers offer MSS, with follow-up testing of either NIPT or proceeding directly to diagnostic testing following screen positive results. If a patient with a screen positive MSS opts for NIPT as the follow-up test, she should be counseled that a normal NIPT result has a residual risk of about 2% for an atypical chromosome abnormality3. Fetal diagnostic testing (CVS or amniocentesis) with microarray will identify aneuploidies as well as atypical chromosome abnormalities. But not all patients choose these invasive tests, perhaps due to the small risk for pregnancy loss.


So, what then is a clinician to do regarding non-invasive screening? NIPT? MSS? Patients should be counseled about their risk for chromosomal abnormalities, and also the benefits and limitations of MSS, NIPT, as well as amniocentesis, and CVS. Some patients prefer going directly to diagnostic testing. Others, wishing to avoid an invasive test, may choose NIPT or MSS. And of course, some patients will decline all testing based on their personal convictions. Patients make informed choices based on these discussions, their own clinical situation, the medical resources available to them, and their personal principles and beliefs. An online resource for patients and providers about these tests and conditions is https://www.lettercase.org/. Furthermore, genetic counseling prior to testing is an option for patients who are clearly undecided.


We’ve certainly come a long way since the early 1980s. The only screening test available then was maternal age, and the only diagnostic test was amniocentesis with a karyotype. Now we have a plethora of MSS tests, NIPT, CVS and amniocentesis with karyotyping and/or microarray at our disposal. Just like at the paint store, more choices are great. But it sure makes choosing even more difficult!


More information about Quest’s prenatal screening offerings can be found  at //www.salesleadsreview.com/home/patients/health-test-info/womens-health/prenatal/during-pregnancy/ or speak to a genetic counselor at 1.866.GENE INFO (1.866.436.3463).



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近十年前,當無創產前檢測(NIPT)第一次成為現實時,許多參與孕婦護理的人(臨床醫生和實驗室人員都一樣)將其視為遊戲規則的改變者。他們認為,篩查染色體異常的標準選擇,即孕產婦血清篩查(MSS),很快就會被淘汰。NIPT是一種檢測唐氏綜合征和某些其他染色體異常的有效方法,具有較高的陽性預測值(PPV)。這意味著假陽性率明顯較低,所以陽性結果很可能意味著胎兒確實患有這種疾病。例如,Quest Diagnostic公司的NIPT檢測QNatal®Advanced對唐氏綜合征的總體陽性預測值(PPV)為98.1%,假陽性率(FPR)僅為0.1%1.相比之下,Quad篩查或First Trimester篩查的唐氏綜合征PPV低於3%,FPR為5%。因此,NIPT可以顯著減少侵入性產前診斷程序(羊膜穿刺術或絨毛膜絨毛取樣)的數量,從而減少程序相關的胎兒丟失。但這並不一定是故事的結局。


MSS是對孕婦血液中某些化學物質的測量,以評估嬰兒患唐氏綜合症和18染色體三體的風險。自20世紀70年代以來,它已被用於篩查開放性神經管缺陷(ONTD),自20世紀80年代以來,唐氏綜合征,自20世紀90年代以來,18 -三體。除了唐氏綜合征和18染色體三體外,篩查陽性的MSS也可能被偶然確定為其他非典型染色體異常。例如,唐氏綜合症或18號三體篩查陽性的女性,其胎兒可能有不同的、不太常見的染色體異常。事實上,一項研究發現,異常的前三個月篩查發現了55%的異常染色體異常2.一些醫生使用MSS生化水平獨立篩查有並發症風險的孕婦,如先兆子癇、出生體重過低、早產或胎兒死亡。AFP (α胎蛋白)是MSS的一部分,是脊柱裂的關鍵預測因子,與染色體異常無關。








  1. Guy C, Haji‐Sheikhi F,Rowland CM,等。平均或高風險孕婦胎兒非整倍體的產前無細胞DNA篩查:來自美國一家大型臨床實驗室的結果。Mol Genet Genomic Med.2019; e545。https://doi.org/10.1002/mgg3.545
  2. 聯合早期妊娠篩查對非典型染色體畸變的產後診斷的檢出率和剩餘風險。產前診斷.2020; 40:852 - 859。https://doi.org/10.1002/pd.5698
  3. 胎兒染色體異常的篩查。ACOG慣例公告第226號。美國婦產科醫師學會。比較。Gynecol2020年,136年。
Jo Ellyn C. Taylor, MS, CGC