|Subject:||Cell-Free Fetal DNA-Based Prenatal Screening for Fetal Aneuploidy|
|Policy #:||GENE.00026||Current Effective Date:||04/16/2013|
|Status:||Reviewed||Last Review Date:||02/14/2013|
This document addresses cell-free fetal DNA-based prenatal screening for fetal aneuploidies, including but not limited to Trisomy 13 (Patau Syndrome), Trisomy 18 (Edwards Syndrome) and Trisomy 21 (Down syndrome) using sequence analysis of cell-free fetal DNA in maternal plasma.
For additional information, please refer to:
Cell-free fetal DNA-based prenatal screening for fetal aneuploidy (trisomy 13, 18, and 21) is considered medically necessary when all of the following criteria are met:
Investigational and Not Medically Necessary:
Cell-free DNA-based prenatal screening for fetal aneuploidy (trisomy 13, 18, 21) is considered investigational and not medically necessary for individuals not meeting the criteria above, including women not at high risk for fetal aneuploidy and for women with a current multiple gestation pregnancy.
New developments in screening methods for fetal chromosomal abnormalities have increased the number of options available to pregnant women. Historically, screening options in the first trimester included nuchal translucency testing along with measurement of pregnancy-associated plasma protein A and human chorionic gonadotropin. Screening options in the second trimester included serum screening using triple or quadruple bio-marker screening and ultrasonography. Individuals also had the option of choosing a combination of first- and second-trimester screening in an integrated, stepwise sequential or contingent sequential fashion. For women who did not present until the second trimester, the quadruple screen was recommended.
Aneuploidies of chromosomes 13, 18, 21, X, and Y are the most frequently represented chromosome anomalies detected in prenatal specimens. Historically, the standard of care for the prenatal diagnosis of chromosome anomalies is amniocentesis, chorionic villus sampling (CVS) or cordocentesis. These invasive tests carry a significant risk of pregnancy loss and are generally offered only to those women at high risk of carrying an affected fetus. Because of the high risk of pregnancy loss, researchers are exploring the use of non-invasive methods to prenatally diagnose fetal chromosomal anomalies. While these newer techniques may help avoid invasive genetic testing, it is important to note that genetic testing should be offered in a setting with adequately trained health care professionals to provide appropriate pre-test and post-test counseling. An individual with a positive cell free fetal DNA test result should be offered invasive prenatal diagnostic testing (chorionic villus sampling or amniocentesis) for confirmation of test results.
Approximately 10% of circulating cell-free DNA in maternal plasma at the end of the first trimester is of fetal origin (Handley 2010). Researchers are investigating the use of fetal-specific DNA sequences in maternal plasma as a non-invasive means to detect fetal aneuploidies such as trisomy 13, 18 and 21. These tests utilize what has been termed "massively parallel DNA sequencing" or "next generation DNA sequencing" to identify an increased or decreased representation of chromosomes associated with fetal aneuploidies. Millions of DNA fragments (fetal and maternal) are sequenced and the number of sequences specific to each chromosome is determined. The proportion of sequence fragments representing these chromosomes has been shown to be greater in the maternal blood of fetuses with trisomy. The test involves the extraction and purification of cell-free DNA from maternal plasma and sequence analysis of DNA fragments. For each fragment, a short sequence (35-50 base pairs) or "tag" is identified and compared with a human genome reference standard to identify its chromosome of origin. The analysis creates a "z-score" representing the number of standard deviations from the mean (Chiu, 2009).
One of the shortcomings of massively parallel DNA sequencing is that it is not selective in the chromosomal origin of the sequenced DNA fragments. As an example, chromosome 21 represents only approximately 1.5% of the human genome, therefore, using massively parallel DNA sequencing, it is necessary to sequence many millions of fragments to ensure a sufficient count of chromosome 21. As an alternative to overcome these limitations, researchers are investigating another technique, digital analysis of selected regions (DANSR™) which entails selective sequencing of loci from only the chromosomes that are under investigation. Researchers have also investigated the use of the fetal-fraction optimized risk of trisomy evaluation (FORTE) by extending the process of chromosome-selective sequencing to assay nonpolymorphic and polymorphic loci, where fetal alleles differ from maternal alleles. This allows the simultaneous determination of chromosome proportion and fetal fraction (Ashoor 2012; Sparks 2012a; Sparks 2012b).
Trisomy 21 (Down syndrome)
Chiu and colleagues (2008) used these techniques to non-invasively detect fetal trisomy 21. The study tested 28 first and second trimester maternal plasma samples, 14 known to be trisomy 21 and 14 known to be euploid fetuses using full karyotyping. All 14 trisomy 21 and 14 euploid fetuses were correctly identified suggesting that this type of sequence analysis of cell-free DNA in maternal plasma might be used to detect trisomy 21 during the first trimester.
Ehrich and colleagues (2011) evaluated a multiplexed (multiple simultaneous sample analysis) massively parallel sequencing (MPS) assay for non-invasive trisomy 21 detection using circulating cell-free fetal DNA. A total of 480 archived plasma samples from high-risk pregnant women who had undergone invasive prenatal testing were analyzed. Of the 480 prospectively collected samples, 449 samples could be evaluated. Investigators were blinded to karyotype status of the samples. All 39 (100%) of trisomy 21 samples were identified using sequence analysis of maternal plasma DNA. One (0.2%) of the 410 euploid samples was misidentified as trisomy 21. The authors reported a sensitivity of 100% (95% CI, 89%-100%) and a specificity of 99.7% (95% CI 98.5% to 99.9%). The researchers concluded that this study demonstrated that plasma DNA sequencing is a viable method for the non-invasive detection of fetal trisomy 21 and warrants clinical validation in a larger multicenter study.
Using a modified testing protocol and different sequencing platform, Chiu and colleagues (2011) analyzed 86 samples of women at high risk for trisomy 21 based on current prenatal screening testing and who subsequently underwent invasive prenatal testing and were found to carry fetuses with trisomy 21. Using a z-score cutoff of 3 and a 2-plex (2 specimens analyzed simultaneously) Genome AnalyzerIIx DNA sequencing platform, sensitivity was 100%, specificity 97.9% with a positive predictive value (PPV) of 96.6% and negative predictive value (NPV) of 100%. Diagnostic performance was much lower using an 8-plex testing protocol with a sensitivity of only 79.1%, specificity 98.9%, PPV 91.9%, and NPV 96.9%. The authors compared their results to the reported performance of the standard three marker screening test with an NPV of 95% (5 % false positive rate). They suggest that the data from this study indicate the main value of maternal plasma DNA sequencing is to rule out trisomy 21 and could be used to stratify pregnancies whose risk for trisomy 21 warrants invasive amniocentesis or chorionic villus sampling (CVS).
Palomaki and colleagues (2011) reported the findings of a validation study of 4,664 women at high risk for trisomy 21 (maternal age, bio-marker screening tests, and/or fetal ultrasound.) Fetal karyotyping was compared with DNA sequence analysis in 212 cases of trisomy 21 and 1,484 matched euploid cases. Maternal blood samples were drawn and sent to two independent, CLIA-certified laboratories for testing. DNA was sequenced using a 4-plex protocol and the HiSeq 2000™ sequencing platform. Of the 4,664 high risk cases, 279 were excluded from analysis (inadequate specimen, multiple gestations, fetal death, karyotype not available). Five percent (218) were found to have trisomy 21 based on karyotyping and 3,930 were euploid. The analysis was limited to the first 212 trisomy 21 cases. Using a z-score of 3, trisomy 21 was detected in 209 of the 212 cases. Sensitivity was reported as 98.6%, false positive rate 0.2%. A subset analysis performed by an independent laboratory confirmed these results.
The International Society for Prenatal Diagnosis (ISPD, 2011) issued a statement addressing prenatal detection of Down syndrome using MPS. The ISPD states that MPS "is not fully diagnostic and therefore constitutes an advanced screening test. Accordingly, confirmation of MPS positive results through invasive testing would still be required. It is also important to recognize that for women who are screen-positive using current screening protocols, Down syndrome represents only about half of the fetal chromosomal abnormalities identified through amniocentesis and CVS". The ISPD has also taken the position that "ISPD does not endorse the ad-hoc use of MPS testing in women at lower risk, outside a formal protocol that considers the overall best combination of tests, their impact on screening performance and patient acceptability.
The National Society of Genetic Counselors (NSGC) issued a position statement that supports the use of non-invasive prenatal testing and non-invasive prenatal diagnosis (NIPT/NIPD) as "an option for patients whose pregnancies are considered to be at an increased risk for certain chromosome abnormalities." The NSGC also states that noninvasive prenatal test "results should not be considered diagnostic at this time, and any abnormal results should be confirmed through a conventional prenatal diagnostic procedure, such as chorionic villus sampling or amniocentesis." With regards to massive parallel sequencing (MPS), the NSGC states that while there are clinical studies demonstrating the ability of MPS to detect abnormalities in chromosomes 13, 18 and 21, "MPS has not yet been proven efficacious in detecting other chromosomal abnormalities or single-gene disorders, and clinical trials for other technologies have not yet been published. NSGC recommends that pretest counseling for NIPT include information about the disorders that it may detect, its limitations in detecting these conditions, and its unproven role in detecting other conditions" (NSGC, 2012).
The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women be offered prenatal assessment for fetal aneuploidy either by screening or invasive prenatal diagnosis, regardless of maternal age. In a joint opinion statement, the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine have concluded that cell-free fetal DNA testing is one tool that can be used as a primary screening test in women at increased risk of aneuploidy. ACOG also recommends that this test may be appropriately used as a follow-up test for women with a positive first-trimester or second-trimester screening test result (ACOG, 2012).
Individuals considered at high risk for fetal aneuploidy include:
Structural chromosome rearrangements such as inversions, translocations and deletion may occur de novo or as a result of a parental chromosome rearrangement. Fusion at or near the centromere of the five acrocentric chromosomes (Robertsonian translocation) is one of the most common balanced structural rearrangements. Simple reciprocal translocations involve exchange of material between two chromosomes. A break occurs in one arm of each, and chromosome material distal to the break swaps positions. Balanced carriers are entirely normal, having no gain or loss of chromosome material, but they are at risk of having chromosomally unbalanced offspring or miscarriages due to malsegregation at meiosis. The extent of the chromosome imbalance depends on the particular translocation. Non-invasive testing of cell free DNA in maternal blood has the potential to provide valuable information to those individuals who are suspected of having a balanced Robertsonian translocation with increased risk of trisomy 21 or trisomy 13.
The ACOG recommendations indicate that "cell free fetal DNA testing should be an informed patient choice after pretest counseling and should not be part of routine prenatal laboratory assessment." The ACOG recommendations also point out that "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. " While ACOG acknowledges that cell free fetal DNA has tremendous potential as a screening tool, the specialty society also cautions that negative cell free fetal DNA test results do not ensure an unaffected pregnancy. Although rare, false positive test results have been observed and reported in the literature. For this reason, individuals with a positive test result should be referred for genetic counseling and should be offered invasive prenatal diagnosis for confirmation of test results. ACOG also acknowledges that in a small percentage of cases, a cell free fetal DNA result will not be obtainable (ACOG, 2012).
Sehnert and colleagues (2011) investigated the ability of massively parallel DNA sequencing of cell-free fetal DNA from maternal blood to detect trisomy 18. Blood samples were collected from 1014 female participants at 13 clinics in the United States before they underwent an invasive prenatal procedure. All samples were processed to plasma, and the DNA retrieved from 119 samples underwent massively parallel DNA sequencing. Fifty-three sequenced samples came from women with an abnormal fetal karyotype. In order to minimize the intra- and interrun sequencing variation, the researchers developed an algorithm by using normalized chromosome values from the sequencing data on a training set of 71 samples with 26 abnormal karyotypes. The classification process was then evaluated on an independent test set of 48 samples with 27 abnormal karyotypes. Mapped sites for chromosomes of interest in the sequencing data from the training set were normalized individually by calculating the ratio of the number of sites on the specified chromosome to the number of sites observed on an optimized normalizing chromosome (or chromosome set). Threshold values for trisomy or sex chromosome classification were then established for all chromosomes of interest, and a classification schema was defined. Sequencing of the independent test set led to 100% of the trisomy 21 (13 of 13) samples and trisomy 18 (8 of 8) samples being correctly identified. The algorithm also correctly identified the presence of trisomy 21 in two sets of twin pregnancies with at least 1 affected fetus and one case of trisomy 9. The authors concluded that massively parallel sequencing is capable of detecting multiple fetal chromosomal abnormalities from maternal plasma when an optimized algorithm is used.
Researchers are also investigating if maternal cell-free fetal DNA sequencing has the capability to detect other aneuploidies, such as trisomy 18 and 13. In a study by Palomaki and colleagues (2012) and sponsored by the Women and Infants Hospital of Rhode Island in collaboration with Sequenom Center for Molecular Medicine (clinicaltrials.gov NCT00877292), the performance of maternal cell-free fetal DNA sequencing for the detection of trisomy 18 and 13 was a secondary endpoint. Of the 1,988 pregnancies with matched euploid controls, 212 samples were identified with trisomy 21, 62 samples with trisomy 18, and 12 samples with trisomy 13. Three trisomy 18 samples failed due to the fetal fraction being lower than the prespecified lower limit (4%). The detection rate for trisomy 18 among the interpreted samples was 59/59 (100%). Among the 12 pregnancies with trisomy 13, the detection rate for trisomy 13 was 11/12 (91.7%). One trisomy 13 sample was signed out as normal (false-negative). Overall, testing failed to provide a clinical interpretation in 17 participants (0.9%); three of which had a trisomy 18 pregnancy.
Bianchi and colleagues (2012) prospectively examined the diagnostic accuracy of massively parallel sequencing (the verifi™ Prenatal Test) to detect whole chromosome fetal aneuploidy in maternal plasma. Blood samples were collected in a prospective, blinded study from 2,882 female participants undergoing prenatal diagnostic procedures at 60 locations in the United States. An independent biostatistician selected all singleton pregnancies with any abnormal karyotype and a balanced number of randomly selected pregnancies with euploid karyotypes. From a pool of 2625 specimens, 532 (20%) maternal plasma specimens were tested. The verifi™ test correctly identified 89 of 89 cases (100%) of trisomy 21, 35 of 36 cases (97.2%) of cases of trisomy 18, 11 of 14 cases (78.6%) of trisomy 13 and 15 of 16 cases (93.8%) of monosomy X. The gender of fetuses was also determined with 232 of 233 cases (99.6%) of female fetuses being accurately identified and male fetuses correctly identified in 184 of 184 cases (100%). No false positives for aneuploidies of chromosomes 13, 18 or 21 were identified, but there was one specimen that was incorrectly identified as monosomy X. The researchers concluded that this test is highly accurate and can be incorporated into prenatal aneuploidy screening algorithms to reduce the incidence of invasive procedures. At the time of this review, we were unable to identify any other studies where this data was replicated.
Sparks and colleagues (2012b) explored the development of a novel prenatal assay based on selective analysis of cell-free DNA in maternal blood for the evaluation of fetal trisomy 21 and trisomy 18. Two hundred ninety-eight pregnancies, including 39 trisomy 21 and seven trisomy 18 confirmed fetal aneuploidies, were analyzed using DANSR™. Cell-free DNA from maternal blood samples was analyzed using DANSR™ assays for loci on chromosomes 21 and 18. The products from 96 separate subjects were pooled and sequenced together. A standard Z-test of chromosomal proportions was used to distinguish aneuploid samples from average-risk pregnancy samples. DANSR™ aneuploidy discrimination was evaluated at various sequence depths. At the lowest sequencing depth of 204 000 sequencing counts per sample, average-risk cases where distinguished from trisomy 21 and trisomy 18 cases. Increasing the sequencing depth to 410 000 counts per sample substantially improved separation of aneuploid and average-risk cases. A further increase of the sequencing depth to 620 000 counts per sample resulted in only marginal improvement. This depth of sequencing represents less than 5% of that required by massively parallel shotgun sequencing approaches. The researchers concluded that DANSR™ enables highly accurate, cost efficient and scalable non-invasive fetal aneuploidy assessment.
Ashoor and colleagues (2012) assessed the prenatal detection rate of trisomy 21 and 18 and the false-positive rate by chromosome-selective sequencing of maternal plasma cell–free DNA. In this nested case-control study, cell-free DNA was examined in plasma that was obtained at 11-13 weeks before chorionic villous sampling from 300 euploid pregnancies, 50 pregnancies with trisomy 21, and 50 pregnancies with trisomy 18. The laboratory personnel were blinded to fetal karyotype. Risk scores for trisomy 21 and 18 were assigned for 397 of the 400 samples that were analyzed. In all 50 cases of trisomy 21, the risk score for trisomy 21 in 47 cases was greater than or equal to 99%, and the risk score for trisomy 18 was less than or equal to 0.01%. In the 50 cases of trisomy 18, the risk score for trisomy 21 was less than or equal to 0.1%; for trisomy 18, the risk score was greater than or equal to 99% in 47 cases. In three of the 300 euploid pregnancies (1%), no risk score was provided because amplification and sequencing failed. In the remaining 297 cases, the risk score for trisomy 21 was less than or equal to 0.01%; for trisomy 18, the risk score was less than or equal to 0.1% in 295 cases, was 0.04% in 1 case, and was 0.23% in one case. Overall, the sensitivity was 100% (50/50 cases) for the detection of trisomy 21 and was 98% (49/50 cases) for the detection of trisomy 18; specificity was 100% (297/297 cases). The authors concluded that the DANSR™ assay with FORTE algorithm is a promising method for detecting fetal trisomy 21 and 18 from cell free DNA in maternal blood during the first trimester of pregnancy. The authors also acknowledged that additional research is needed to investigate the accuracy of the test in intermediate-risk and low-risk pregnancies and to expand the spectrum of aneuploidies that could be detected by analysis of maternal plasma cell-free DNA.
In another study, Sparks and colleagues (2012a) evaluated the use of the DANSR™ assay and FORTE algorithm for the prenatal evaluation of risk for fetal trisomy 21 and trisomy 18 using cell-free DNA obtained from maternal blood. The researchers assayed cell-free DNA from a training set and a blinded validation set of pregnant females, consisting of 250 euploidy, 72 trisomy 21, and 16 trisomy 18 pregnancies. The researchers then used the DANSR™ assay in combination with FORTE algorithm to determine trisomy risk for each participant. Overall, 163/171 subjects in the training set passed quality control criteria. Using a Z statistic, 35/35 trisomy 21 cases and 7/7 trisomy18 cases had Z score greater than 3 and 120/121 eupoloid cases had Z score less than 3. FORTE produced an individualized trisomy risk score for each participant and correctly identified all trisomy 21 and trisomy 18 cases from euploid cases. All 167 subjects in the blinded validation set passed quality control and FORTE performance matched that observed in the training set correctly identified 36/36 trisomy 21 cases and 8/8 trisomy18 cases from 123/123 euploic cases. The authors concluded that digital analysis of selected regions in conjunction with FORTE enable accurate, scalable non-invasive fetal aneuploidy detection.
In summary, several studies support the clinical validity of DNA based testing of maternal plasma in women known to be at risk for a trisomy 21 pregnancy when compared with karyotype analysis following amniocentesis or CVS (Chiu, 2008; Fan, 2008; Chiu, 2011; Ehrich, 2011; Palomaki, 2011, Ashoor, 2012). There are also studies supporting the clinical validity of DNA based testing of maternal plasma in women at risk for trisomy 13, 18 and trisomy X (Sehnert, 2011; Ashoor, 2012; Bianchi, 2012; Palomaki, 2012, Sparks, 2012a; Sparks, 2012b). Several of the studies used different protocols and non-standard sequencing platforms, software algorithms and analysis. Although gestational age and maternal weight have been shown to affect test results, most studies did not control for these variables. Also, various test protocols were used in the studies and several of the earlier studies were quite small. However, in spite of these limitations, ACOG, ISPD and NSGC have concluded that there is sufficient evidence to support the use of cell free fetal DNA-based non-invasive screening for aneuploidy in select individuals at high risk for fetal aneuploidy. These specialty organizations also recommend that any abnormal results be confirmed through conventional prenatal diagnostic procedure such as chorionic villus sampling or amniocentesis (ACOG, 2012; ISPD, 2011; NSGC, 2012). The advantages of antenatal screening include increasing the odds of identifying an abnormal fetus and reducing the number of invasive diagnostic tests and procedure-related losses of normal fetuses. The disadvantage of screening is that not all aneuploid fetuses are identified with screening (AAFP, 2009). ACOG also cautions that cell free DNA testing as a screening tool provides information regarding only trisomy 21, trisomy 18 and in some laboratories, trisomy 13. DNA-based non-invasive prenatal screening for aneuploidy is currently not recommended for women not at high risk for aneuploidy or in cases of multiple gestations because there is a lack of outcome data for these populations. There is also the possibility that in a small percentage of cases, a DNA-based non-invasive prenatal screening result will not be obtainable (ACOG, 2012).
There are currently several commercially available laboratory developed tests which analyze circulating cell-free DNA to identify increased representation of various chromosomes. These tests include but are not necessarily limited to the following:
For all pregnancies, the baseline risk of some type of birth defect occurring is 3 - 4 percent. The severity of such defects varies greatly, and is a reflection of the wide range of possible inherited mutations or genetic variants. Spontaneous mutations can rise in the gametes, embryo or fetus or be the result of epigenetic alterations or environmental influences. Maternal factors that increase the risk of having a child with a congenital anomaly or genetic condition include advanced maternal age (over the age of 35 at the time of delivery), diabetes, obesity and exposure to teratogenic factors such as viral infections and alcohol (Bodurtha, 2012).
Down syndrome (trisomy 21)
Down syndrome is the result of one of three types of abnormal cell division involving chromosome 21. Any of these three abnormal types of cell division result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome. The genetic variations that can cause Down syndrome include:
Most of the time, Down syndrome isn't inherited but occurs de novo as a result of a mistake in cell division during the development of the egg, sperm or embryo. Translocation Down syndrome is the only form of the disorder that can be inherited. When translocations are inherited, the parent (father or mother) is a balanced carrier of the translocation (the parent has some rearranged genetic material, but no extra genetic material). Balanced carriers exhibit no signs or symptoms of Down syndrome, but they can pass the translocation on to their offspring.
Trisomy 21 or Down syndrome is the most common chromosome abnormality in humans with an incidence of approximately 1 in 800 live births (Driscoll, 2009). Although the risk of trisomy 21 increases with maternal age, most trisomy 21 pregnancies occur in women younger than age 35. Screening for trisomy 21during the first trimester involves a combination of maternal serum beta human chorionic gonadotropin (β-HCG), maternal serum pregnancy-associated plasma protein-A (PAPP-A) and ultrasound measurement of nuchal translucency. These markers along with maternal age are used to estimate the risk of a trisomy 21 fetus. Sensitivity with this screening panel is reported to be 85% with a false positive rate of 5%. Invasive testing to diagnose trisomy 21 prenatally includes amniocentesis or CVS to obtain fetal cells for karyotyping. Both procedures involve risk of pregnancy loss and are generally performed only on women whose risk of trisomy 21 based on the biochemical screening profile and/or ultrasound findings is greater than the risk of pregnancy loss from an invasive diagnostic test (approximately 0.5% for amniocentesis and 0.5-1.0% for CVS).
Monosomy X (Turner syndrome, monosomy XO)
Turner syndrome results when one normal X (sex) chromosome is present in a female's cells and the other sex chromosome is missing or structurally altered. The missing genetic material affects the development of the female both before and after birth. The most common feature of Turner syndrome is short stature, which generally becomes evident by age 5. An early loss of ovarian function is also very common. Affected girls may not undergo puberty unless they receive hormone therapy and most are infertile. A small percentage of females with Turner syndrome retain normal ovarian function through young adulthood. Other features of Turner syndrome include extra folds of skin on the neck (webbed neck), a low hairline at the back of the neck, lymphedema of the extremities, skeletal abnormalities, or kidney problems. One third to one half of individuals with Turner syndrome are born with a heart defect which may become life-threatening. Most females with Turner syndrome have normal intelligence; however, developmental delays, nonverbal learning disabilities, and behavioral problems are possible, although these characteristics vary among affected individuals. Turner syndrome occurs in approximately 1 in 2,500 newborn girls worldwide, but it is much more common among pregnancies that do not survive to term (miscarriages and stillbirths).
Trisomy X (Triple X syndrome)
Trisomy X (also known as Triple X syndrome) occurs in approximately 1 in 1,000 newborn girls with five to ten females being born with this condition in the United States each day. Females with the Triple X syndrome have an extra (3) X chromosome instead of the usual pair (2) sex chromosomes. Although this condition is genetic, it is generally not inherited. Instead, it is usually the result of either the mother's egg or the father's sperm not forming correctly, resulting in an extra X chromosome. Females with this condition may be taller than average, but may have no other unusual physical features. Most females with triple X syndrome reach normal sexual development and are able to conceive children. Triple X syndrome is associated with an increased risk of developmental delay of speech and language skills and learning disabilities. Delayed motor skills (sitting and walking) development, hypotonia, as well as behavioral and emotional difficulties are also possible. The severity of these conditions varies widely among affected individuals. Seizure disorder or kidney abnormalities may occur in approximately 10% of the affected females.
Trisomy 13 (Patau syndrome) is the least common (occurring in approximately 1 in 16,000 newborns) and one of the most severe of the autosomal trisomies. Many of the clinical features widely vary; however, severe mental deficiency is a consistent feature in children born with Patau syndrome. Brain malformation, polydactyly, rocker-bottom feet, facial clefting, neural tube defects, missing ribs and heart defects are also generally present. Patau syndrome is frequently recognized at birth by the presence of structural birth defects and poor neurologic performance. Median survival age for infants with Patau syndrome is 2.5 days, with only one in 20 infants surviving longer than 6 months. Although the exact cause of Patau syndrome has not been identified, a significant association is recognized between Patau syndrome and increased maternal age.
Trisomy 18 (Edwards syndrome) occurs in approximately 1 in 5,000 live births. Individuals with trisomy 18 often have intrauterine growth retardation (slow growth prior to birth) and a low birth weight. Affected individuals may have heart defects (atrial septal defect, patent ductus arteriosus, or ventricular septal defect) and abnormalities of other organs that develop before birth. Other features of trisomy 18 include camptodactyly with overlapping fingers, rocker-bottom feet, low-set ears, mental deficiency, microcephaly, micrognathia, undescended testicles, underdeveloped fingernails, and pectus carinatum. Due to the presence of several life-threatening medical problems, many individuals with trisomy 18 die before birth or within their first month of life. Only 5 – 10% of affected individuals live past their first year, and those that do survive often have severe intellectual disability. Like trisomy 13, the development of trisomy 18 is also associated with advanced maternal age.
The American College of Obstetricians and Gynecologists (ACOG, 2007a) Practice Bulletin on screening for fetal chromosomal abnormalities recommends that all women be offered aneuploidy screening before 20 weeks of gestation and that they should be provided the option of invasive testing, regardless of maternal age. In another practice bulletin addressing invasive prenatal testing for aneuploidy, ACOG also recommends that a prenatal diagnostic procedure (amniocentesis, CVS or cordocentesis) should be considered in women of any age at high risk of Down syndrome or other fetal aneuploidies. Individuals at high risk include those with at least one major or two minor fetal structural anomalies in the current pregnancy or chromosomal translocation, inversion, or aneuploidy in themselves or their partner (ACOG, 2007b).
The American Academy of Family Physicians (2009) makes the following recommendations with regards to prenatal screening and diagnosis of fetal chromosomal abnormalities: "Pregnant women of all ages should be offered screening and invasive diagnostic testing for chromosomal abnormalities before 20 weeks' gestation. New developments in screening methods have increased the number of options for patients. Diagnostic options include chorionic villus sampling in the first trimester and amniocentesis in the second trimester. Screening options in the first trimester include nuchal translucency testing in combination with measurement of pregnancy-associated plasma protein A and human chorionic gonadotropin. Nuchal translucency testing alone is not as effective. Screening options in the second trimester include serum screening using triple or quadruple screening, and ultrasonography."
As mentioned in the Rationale section above, there are currently several tests available for identifying an increased representation of chromosomes 21, 18 and 13. These tests include, but are not limited to the MaterniT21™ and the MaterniT21™ Plus tests (Sequenom Center for Molecular Medicine [Grand Rapids, MI]), the verifi™ Prenatal Test (Verinata Health Inc. [Redwood City, CA]) and the Harmony Prenatal Test™ (Aria Diagnostics, San Jose, California).
Aneuploidy: A condition where there are either fewer or more than the normal number of chromosomes present in cells of a person's body.
Circulating cell-free fetal DNA (ccffDNA): The result of the breakdown of fetal cells (mostly placental) which clears from the maternal system within hours.
Chorionic villus sampling: A prenatal test to detect birth defects which involves retrieval and examination of tissue from the chorionic villi (placenta).
Camptodactyly: Permanently closed (flexed) fingers.
Euploidy: The state of having a balanced set of chromosomes.
Holoprosencephaly: Failure of the forebrain to divide into lobes or hemispheres.
Hypotonia: Weak muscle tone.
Microcephaly: A small head.
Micrognathia: A small jaw.
Monosomy: The absence of one chromosome of the usual pair to (two) chromosomes.
Monosomy X: A congenital disorder caused by the absence of one X sex chromosome (the individual has only one X sex chromosome rather than the usual pair [either two Xs or one X and one Y sex chromosome]); also called Turner syndrome and monosomy XO.
Pectus carinatum: An unusual shaped chest.
Polydactyly: Extra fingers or toes.
Robertsonian translocations: Chromosomal rearrangement in humans that occurs in five acrocentric (long and short arm) chromosome pairs (13, 14, 15, 21, and 22). These translocations are also called "whole-arm" or centric-fusion translocations. During a Robertsonian translocation, the chromosomes break at their centromeres and the long arms fuse to form a single chromosome with a single centromere. The short arms also join, but usually contain nonessential genes and are usually lost within a few cell divisions.
Rocker-bottom feet: A rigid flatfoot deformity.
Trisomy: The presence of three chromosomes, rather than the usual pair of (two) chromosomes.
Trisomy X: A congenital disorder caused by having an extra copy of chromosome X; also called Triple X syndrome.
Trisomy 13: A congenital disorder caused by having an extra copy of chromosome 13; also called Patau syndrome.
Trisomy 18: A congenital disorder caused by having an extra copy of chromosome 18; also called Edwards syndrome.
Trisomy 21: A congenital disorder caused by having an extra copy of chromosome 21; also called Down syndrome.
The following codes for treatments and procedures applicable to this document are included below for informational purposes. A draft of future ICD-10 Coding (effective 10/01/2014) related to this document, as it might look today, is included below for your reference. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.
When services may be Medically Necessary when criteria are met:
|81479||Unlisted molecular pathology procedure [when specified as DNA sequencing to detect fetal aneuploides]|
|81599||Unlisted multianalyte assay with algorithmic analysis [when specified as DNA sequencing to detect fetal aneuploides]|
|84999||Unlisted chemistry procedure [when specified as DNA sequencing to detect fetal aneuploidies]|
|All diagnoses, including, but not limited to, the following:|
|796.5||Abnormal finding on antenatal screening|
|V23.81||Supervision of elderly primigravida|
|V23.82||Supervision of elderly multigravida|
|V28.89||Other specified antenatal screening (genomic)|
|V82.79||Other genetic screening|
|ICD-10 Diagnosis||ICD-10-CM draft codes; effective 10/01/2014:|
|All diagnoses, including, but not limited to, the following:|
|O09.511-O09.529||Supervision of elderly primigravida and multigravida|
|O28.0-O28.9||Abnormal findings on antenatal screening of mother|
|Z13.79||Encounter for other screening for genetic and chromosomal anomalies|
|Z31.438||Encounter for other genetic testing of female for procreative management|
When services are Investigational and Not Medically Necessary:
When medical necessity criteria are not met or when the code describes a procedure indicated in the Position Statement section as investigational and not medically necessary.
Peer Reviewed Publications:
Government Agency, Medical Society, and Other Authoritative Publications:
|Web Sites for Additional Information|
Harmony Prenatal Test™
Massively parallel DNA sequencing
Triple X syndrome
verifi™ Prenatal Test
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|Review||02/14/2013||Medical Policy & Technology Assessment Committee (MPTAC) review. Updated review date, References and History sections.|
|Revised||12/17/2012||MPTAC review. Title changed to "Cell-free DNA-Based Prenatal Screening for Fetal Aneuploidy." Position changed to consider cell-free DNA-based prenatal screening for fetal aneuploidy medically necessary when criteria are met. Investigational and not medically necessary statement revised to stipulate testing is not covered in women not at high risk for fetal aneuploidy and for women with a current multiple gestation pregnancy. Rationale, Background/Overview, Definitions, References and History sections updated. Updated Coding section to include 01/01/2013 CPT changes.|
|Revised||08/09/2012||Medical Policy & Technology Assessment Committee (MPTAC) review. Expanded scope of document to address Trisomies 13, 18, 21, X and monosomy X. Title changed to "DNA-Based Noninvasive Prenatal Diagnostic Testing for Fetal Aneuploidy. Revised position statement to specifically address DNA-based noninvasive prenatal diagnostic testing for trisomies 13, 18 and X. Updated the Rationale, Background/Overview, Definitions, References, Index and History sections.|
|New||05/10/2012||MPTAC review. Initial document development.|