Advantages of Fetal Marker Scanning - Essay Example

Contents Introduction…………………………………………………………2 What is fetal marker scanning? …………………………………….3 Detecting chromosomal abnormalities………………………………5 Advantages of fetal marker scanning……………………………….9 Disadvantages of fetal marker scanning……………………………11 Conclusion……………………………………………………………15 Reference List……………………………………………………….16. Introduction Since ultrasound was first use in the late 1950’s, it has been a very helpful diagnostic tool in Obstetric. Prenatal ultrasound (also called fetal ultrasound or fetal sonography) has become an almost regular part of the antenatal care during visits to the obstetrician (Woo, 2005). Ultrasound (sonogram) is used to provide detailed images of the fetus and uterus during pregnancy.  The ultrasound probe emits sound waves which give an image the baby and placenta. Therefore, its painless and it does not cause any harm to the fetus or the mother and it has different purpose at different stages during the pregnancy.   During the first trimester, ultrasound is used to predict an accurate due date, establish multiple pregnancies, and look for causes of pregnancy complications. . It is important to know that ultrasound is a screening tool.  It will not be able to detect when there is an increased risk of genetic or chromosomal birth defects.  As in all screening tests, there are false-positives and false-negatives with ultrasound.  Detection of a marker by ultrasound does not mean that the baby definitely has an abnormality.  Many markers discovered by ultrasound, representing normal variation. However, a normal ultrasound does not rule out all abnormalities in some cases, ultrasound can miss some fetal abnormalities (Ultrasound, 2005). The main purpose of prenatal screening is to detect an affected fetus and to prepare parents for the delivery of an affected infant, to allow antenatal or postnatal treatment, to allow early decision of an affected fetus termination and to provide information so that parents may choose between various options (Ibrahim &Newman, 2005). What is fetal marker scanning? Ultrasound can detect a chromosomal abnormalities during the early stages of the pregnancy in which a scan identifies features, called “soft marker”– as a structural change that may indicate an increased probability that the fetus has a chromosomal abnormality (Ibrahim & Newman,2005). Soft markers are usually transient ultrasound features which may indicate a possibility of serious fetal chromosomal abnormality but which in themselves are probably insignificant (Whittle, 1997). Obstetric ultrasound diagnosis of chromosomal anomalies employs a variety of techniques either as a screening procedure for relatively common disorders which identifies an increased possibility of a fetal abnormality in an apparently normal pregnancy, or as a diagnostic procedure for known familial conditions which confirms the existence of an definite anomaly in a fetus believed to be at increased risk (Agarwal, 2003). With high-resolution ultrasound, it is possible to examine fetal anatomy in massive detail. Soft markers are useful in screening for chromosomal abnormalities when considered together with maternal age, but as routine fetal screening may have caused physical or psychological harm to the parents and unborn children (Getz & Kirkengen, 2003). Most of those markers indicating pathology are associated with an abnormal karyotype and because first trimester scans are performed more often, the frequency of marker observation has risen in the same way (Whittle, 1997). Various Soft markers that can be detected by a second-trimester ultrasound scan include choroid plexus cysts (CPCs), renal pelvic dilatation, echogenic foci in the fetal heart or fetal gut (echogenic bowel), talipes, short limbs and nuchal thickening. Most, but not all soft markers are associated with an increased risk for Trisomy 21 (Down syndrome) (Ibrahim& Newman, 2005). Ultrasound performed at 18-20 weeks identifies birth defect and/or ultrasound markers in as many as 50-60% of babies with Down syndrome, however it will not identify markers of down syndrome in all affected babies due to the technical limitation of the ultrasound views (ultrasound, 2005). Ultrasound assessment of marker of Aneuploidy in the second trimester in not recommended as a primary screening test for down syndrome and the timing of this ultrasound should take into account the possible need for further testing and counselling (HGSA/RANZCOG Prenatal diagnosis and screening committee ,2004). Detecting chromosomal abnormalities Ultrasonography is usually done during the first trimester (up to 13 weeks 6 days gestation) for dating, determine of the number of fetuses, and evaluation for early pregnancy defects. In recent times, fetal nuchal translucency (NT) measurement between 11 and 14 weeks gestation, combined with maternal age, has provided a valuable way of screening for trisomy 21 and other chromosome abnormalities. The detection rate of fetuses with trisomy 21 is further increased by combining maternal age, fetal NT thickness, and maternal serum biochemistry (free ß–human chorionic gonadotropin and pregnancy-associated plasma protein-A) (Fong et al ,2004). Nuchal translucency (NT) can be defined as increased when the thickness is more than 3 mm before 15 weeks of gestation and more than 5 mm thereafter (Blandwehr et al, 1996). A thickness of 6 mm or more at 18–20 weeks has also been used (Nyberg et al, 1990) see figure 1. The measurement is in millimeters and tenths of a millimeter by ultrasound set by the Fetal Medicine Foundation (Acacio et al ,2001). Increased NT is also associated with increased risk of Turner syndrome (8%) (Blandwehr et al,1996). Even in the presence of a normal karyotype there is an increased risk of many structural abnormalities (including major cardiac defects, skeletal dysplasias, fetal akinesia, diaphragmatic hernia) as well as a variety of genetic syndromes (Nadel et al, 1993). Figure 1 Sagittal transvaginal US image of a fetus with trisomy 21 shows an increased NT thickness of 8 mm . The skin is elevated along the back due to subcutaneous edema (subcutaneous fluid collection at the back of the neck) (arrow) (Fong et al 2004). Triple Marker Screening for women 35 years of age and older is a useful screening tool to increase or decrease the risk for Down syndrome. However, its greatest limitation is that it detects less than 90% of fetuses with Down syndrome in women between 35 and 39 years of age (Devore& Greggory, 2001). Down syndrome occurs in 1 in 660 births and its incidence is directly proportional to maternal age (Bilardo, 1996). Ten to 40% of Down syndrome fetuses may have further anatomic abnormality, such as a major cardiac anomaly, which can be identified antenataly and raise the risk of aneuploidy significantly. The thickened nuchal fold (>5 mm at 15-21 weeks) is the most reliable “soft marker” of fetal DS, raising the likelihood ratio significantly (Ibrahim& Newman, 2005). Combining maternal, maternal age, serum a-fetoprotein and free B-human chorionic gonadotrophin (B-hCG) in the second trimester of pregnancy has improved detection rates to 63%, for a 5.2% fake-positive rate (Spencer and Carpenter, 1993).In the early 1990, a number of Studies has been established in high risk pregnancies a possible associated between increase Nucal Transulansy and chromosomal defect in first trimester of pregnancy as it shown in table 1 (Snijders , 1996). Table 1 Criteria for diagnosis of increased nuchal transulancey thickness and the presence of associated chromosomal defect (Snijders, 1996). Current evidence suggests that fetuses with Down syndrome are more likely to exhibit shortened long-bone measurements (short humerus or a short femur) compared with the normal population (Nyberg et al, 1993). Choroid plexus cysts are echolucent, well-circumscribed structures found in the choroid plexus(figure2). They represent a normal neuroepithelial folds that subsequently fill with cerebrospinal fluid and cellular debris. The presence of apparently isolated choroid plexus cysts increases the risk of trisomy 18 (Gupta et al, 1997). Figure 2 Chroroid plexus cyst in a 20 weeks mature fetus (Agarwal,2003). Normal intestinal echogenicity varies with gestational age and between patients. Because the intestine has no characteristic structural features, the examination is highly subjective. Hyperechogenic bowel has been found to be a non-clinically significant physiological variant in most instances (approximately 67% of cases) (Fakhry et al, 1986). Cardiac echogenic foci are defined as hyper-echogenicity thought to be located in the chordae tendineae(figure3), not attached to the ventricular walls and moving simultaneously with the atrioventricular valves. Most of these echogenic foci resolve spontaneously. Studies showed that there is a risk of 1 in 500 (0.002%) for trisomy 21 in association with isolated fetal cardiac echogenic foci (Achiron et al, 1992). Figure 3 Enlarged view of fetal heart (19 weeks) showing echogenic cardiac focus in the left ventricle.( Agarwal,2003) In isolation, the association between pelvicalyceal dilatation (PCD) or fetal pyelectasis and chromosomal abnormalities is very small. PCD is diagnosed when the anteroposterior diameter of the renal pelvis is more than 4 mm before 33 weeks of gestation and more than 7 mm thereafter (Corteville et al, 1991). The measurement of nasal bone length in the second trimester seems to provide additional benefits beyond the assessment of presence or absent of nasal bone (Viora et al ,2005).Although the absence of nasal bone is power full marker for DS, however, a short nasal bone is associated with increased possibility for DS in high risk population (Bromley et al 2002) Advantages of fetal marker scanning Ultrasound screening is widely offered to all pregnant women in pregnancy between 16-20 weeks. The availability of information to the parents of possible birth defects of the fetus to enable the parents to decide on various options on treatments. Such information could allow in-utero treatment, or delivery at a specialized hospital for a more postnatal care. This eventually could save the baby’s life and increase the chances of a normal life.  Knowing about the problems before birth provides time to plan the baby's treatment (Chromosomal abnormalities, 2005). One of the main advantages of fetal marker scanning in determining chromosomal abnormalities is that it provides a non-invasive alternative of diagnosis compared to currently available invasive screening test that often are associated with a finite risk of morbidity and mortality to the fetus. The risk associated with these tests and the cost of analysis precludes the adoption of methods for mass screening of pregnant women. Invasive screening test includes several biochemical tests, while CVS, amniocentesis, and fetal blood sampling are invasive diagnostic procedures (Agarwal, 2003). At present, these invasive procedures are standard for the diagnosis of chromosomal anomalies or other genetic defects. Invasive diagnostic is only given on a restricted basis to high-risk pregnancies where the benefit outweighs the risk. In low-risk pregnancies, where there is less likelihood of diagnosing a chromosomal abnormality, prenatal diagnosis generally consists of screening procedures by way of ultrasound and maternal serum biochemistry (Agarwal, 2003). Studies demonstrate that 11-14 weeks ultrasound is effective in diagnosing fetal abnormalities in the high-risk population. Some practisioner also found the 11-14 weeks ultrasound to be 91% effective. While others have reported this to be between 57-89% (Munim&Khowaja,2004).Early detection of fetal abnormalities has advantages compared with detection at 18 weeks gestation it allow time for appropriate initiation therapy. if the parents choose to terminate pregnancy at this stage so the procedure can be done as an out patients basis with more favorable cost-benefit ratio(Fong et al,2004) .Sonogram is included in the second trimester strategies, but the first trimester combined screening become the most cost-effective strategy(Odibo et al ,2005). Moreover, obstetric ultrasound is safer than conventional X-rays. Unlike X-rays, ionizing irradiation is not present in ultrasound, and embryo toxic effects associated with such irradiation should not be significant. Harmful effects in cells of experimental animals or humans however have not been demonstrated in many studies (Woo, 2005). Disadvantages of fetal marker scanning There are some drawbacks to fetal marker scanning of chromosomal abnormalities. Fetal markers scanning my help identify chromosomal abnormalities, however, they may provoke unnecessary anxiety or lead to inappropriate karyotyping and its inherent risk of miscarriage (Abdalla and Beattie, 2001). In some cases, there is uncertainty of the examination results and the possibility of being over-diagnosed or under-diagnosed. In low-risk women, ultrasound is good at ruling out problems, but not as good at detecting them. At present, a regular ultrasound examination detects only 50% of all possible birth defects. However, besides missing some birth defects, a routine ultrasound exam occasionally can suggest that a birth defect is present when none exists. Approximately 1 in 1,000 low-risk women had been told that her baby might have a birth defect, when actually the baby does not. While follow-up exams often show that the baby is healthy, such false alarms can cause intense anxiety for both parents (Ultrasound, 2005). The main problem from the use of ultrasound fetal marker of chromosomal abnormalities are the possible over-diagnosis or under-diagnosis brought when such diagnosis is performed less trained technician, who often use outdated ultrasound equipment. Ultrasound equipment is only as good as its operator (Ultrasound, 2005). The fact that between 15%-84% abnormalities are not detected at time of second trimester scan, mean that many parents are falsely reassured that their baby is normal while some sonograghic feature associated with an underlying abnormality is not evident at 20 weeks or because the sonographer has in sufficient time or skills to examine the fetus details ( chitty ,1999). Many of the problems that are diagnosed during pregnancy are serious, and in many cases the only option to consider is whether to have a termination of the pregnancy, or continue the pregnancy (Perinatal institute, 2005). This would give parents the dilemma in deciding whether or not to termination of pregnancy and some women may wish to consider that option. At whatever stage fetal abnormality is diagnosed, women and their partners need good quality information about the implications of the result and the options open to them. the vast majority of these pregnancies are wanted and the decision of whether to terminate a pregnancy in such circumstances is never easy especially on non-conclusive evidence (Abortion time limits, 2005). In the United States, soft markers confronted physicians with another dilemma. Due to the possibility of litigation, examiners report that they have no choice but to inform their clients about all findings of fetal soft markers (Ibrahim & Newman, 2005). Two American experts independently reported in the year 2000, that at least 5-10% of low-risk women who entered their practices would end up with an `at-risk' label as they received information about the presence of one or more ultrasonographic risk markers in their fetus (Benacerraf, 2000).Considerable difficulty in giving a confident prognosis in screening the low risk population which result in further parental anxiety and in some cases unnecessary termination of pregnancy(chitty ,1999). A Thickened nuchal fold in the second trimester maybe useful in distinguishing unaffected fetuses from those with down syndrome, but the overall sensitivity of this finding it too low for it to be practical screening test for down syndrome(Smith et al,2001).Chroid plexus cyst have also caused controversy when found in isolation marker ,it need confirmation by invasive prenatal testing together with maternal age and presence of other risk factors.(whittle ,1997).They found that ultrasound with multiple screening test in fetus with trisomy 18 yielding the highest detection rate than the ultrasound alone(Brumfield et al ,2000).Furthermore ,the prescence or absence of genetic sonogram modify the risk of DS but combined the maternal biochemical and sonogrghic marker result in higher detection rate than either alone(Nybreg &Souter 2001). The main weakness of fetal soft marker scanning lies in the innate subjectivity in determining the presence of some of the markers, such as echogenic intracardiac focus and echogenic bowel. Although measured parameters such as normative values for limb lengths show substantial variability between investigators, possibly because of the specific populations studied, measurement technique and variability, and/or the threshold chosen to represent a reasonable compromise between sensitivity and specificity (Winter et al…,2000). for a time , a diagnosis parentally worsen the outcome instead of improving it ,in case of a baby delivered earlier or by caesarian while other baby with same condition not diagnosed prenataly may deliver normal(Kmom,2003) .Some time there also ambiguous diagnosis whene radiologist think there might be a problem but cannot say it for sure .even with further ultrasound 's the parents are not sure what the status of the child is ? , with no clear answers, nothing can be done and parents are left with anxiety (Kmom,2003). Conclusion Ultrasound fetal markers scanning is becoming more popular amongst doctors in detecting the early anatomical signs associated with some abnormalities .Ultrasound has different uses at different time during pregnancy .first trimester ultrasound used to predict an accurate due date ,establish twin and triplet pregnancies and look for causes routinely to every pregnant women in the UK in order to identify those at high risk of having an affected child and it has become routine practice in many western countries. screening may include maternal serum screening and ultrasound which can detect both major and minor defects(BMA, 2005).the problem with soft marker is that even with karyotyping abnormalities are excluded , the mother and obstetrician will remain in doubt as to their significant a cause of anxiety. Information about ultrasound marker is relatively new, many of the data come from referral unit and are therefore biased . Soft marker searching required more time and better equipment and training than standard scan .ethically it not be acceptable if identifying these marker may increase anxiety to the parents without prior counseling ( Whittle ,1997). Reference List Abdalla, Mohamed and Bryan Beattie. (2001). Ultrasound screening for chromosomal abnormalities in the second trimester. The Obstetrician & Gynaecologist; Volume: 3, Issue: 3, 147-149. Abortion time limits. (2005). BMA.rog.uk. Available from: [22 Dec. 2005]. Acacio GL, Barini R, Pinto Junior W, Ximenes RL, Pettersen H, Faria M..(2001).Nuchal translucency: an ultrasound marker for fetalchromosomal Abnormalities. Sao Paulo Med J. ; Jan 4;119(1):19-23. Achiron R, Glaser J, Gelernter I, Hegesh J, Yagel S. (1992). Extended fetal echocardiographic examination in detection of cardiac malformation in low risk women. BMJ ;304:671–4 Agarwal, R. (2003). Prenatal Diagnosis of Chromosomal Anomalies: Pictorial Essay. Ind J Radiol Imag; 13:2:173-187 Benacerraf, B.R., (2000). Should sonographic screening for fetal Down syndrome be applied to low-risk women?. Ultrasound in Obstetrics and Gynecology; Volume 15 Issue 6:451-455. Bilardo C. (1996). Second trimester ultrasound markers for fetal aneuploidy. Early Hum Dev.; 47Suppl:S31–3. Blandwehr JB, Johnson MP, Hume RF, Yaron Y, Sokol RJ, Evans MI. (1996). Abnormal nuchal findings on screening ultrasonography: aneuploidy Stratification on the basis of ultrasonographic anomaly and gestational age at detection. Am J Obstet Gynecol ;175:995–9. Bryann Bromley, MD, Ellice Lieberman, MD, DrPH, Thomas D. Shipp, MD and Beryl R. Benacerraf, MD.(2002). Fetal Nose Bone Length A Marker for Down Syndrome in the Second Trimester : J Ultrasound Med; 21:1387-1394 • 0278-4297. BRUMFIELD CYNTHIA G, MD, KATHARINE D. WENSTROM, MD, JOHN OWEN, MD and RICHARD O. DAVIS, MD.(2000). Ultrasound Findings and Multiple Marker Screening in Trisomy 18: Obstetrics & Gynecology; 95:51-54. Chromosonal abnormalities. (2005). March of Dimes. Available from: http://www.marchofdimes.com/professionals/681_1209.asp> [01 Dec. 2005]. Chitty LS.,(1999),Should routine ultrasound examination be performed by indication only ? ,The First Word Congress on : Controversies in Obstetrics ,Gynecology &Infertility .Prague , Czech Republic . Corteville JE, Gray DL, Crane JP. (1991). Congenital hydronephrosis: correlation of feral ultrasonographic findings with infant outcome. Am J Obstet Gynecol ;165:384–8 Devore, Greggory R.,(2001) The genetic sonogram: its use in the detection of chromosomal abnormalities in fetuses of women of advanced maternal age,Prenatal Diagnosis ;Volume 21, Issue 1 , Pages 40 - 45 Fakhry J, Reiser M, Shapiro LR, Schechter A, Pait LP, Glennon A. (1986). Increased ecogenicity in the lower fetal abdomen: a common normal variant in the second trimester. J Ultrasound Med ;5:489–92. Fong, Katherine W., Ants Toi, Shia Salem, Lisa K. Hornberger, David Chitayat, MD, Sarah J. Keating, Fionnuala McAuliffe, and Jo-Ann Johnson. (2004). Detection of Fetal Structural Abnormalities with US during Early Pregnancy. Radiographics. ;24:157-174. Getz L, Kirkengen AL.(2003). Ultrasound screening in pregnancy: advancing technology, soft markers for fetal chromosomal aberrations, and unacknowledged ethical dilemmas. Soc Sci Med.; 56(10):2045-57. Gupta JK, Khan KS, Thornton JG, Lilford RJ. (1997). Management of fetal choroid plexus cysts. Br J Obstet Gynaecol ;104:881–6. HGSA/RANZCOG & Screening committee .(2004) best practice guideline on antenatal screening for down syndrome and other fetal Aneuploidy. Ibrahim, Hythum Ibrahim, and Michael Newman. (2005). Ultrasound Soft Markers of Chromosomal Abnormalities:An Ethical Dilemma for Obstetricians. The Internet Journal of Gynecology and Obstetrics. 2005. Volume 4 Number 1 Kmom .(2003). Prenatal Testing: Ultrasound Safety and Accuracy. Available from http://www.plus-size-pregnancy.org/Prenatal%20Testing/prenataltest-ultrasoundsafety.htm#Ultrasound%20for%20Detecting%20Fetal%20Abnormalities.[2.Jan.2006] Nadel A, Bromley B, Benacerraf BR. (1993). Nuchal thickening or cystic hygromas in first and early second trimester fetuses: prognosis and outcome. Obstet Gynecol ;82:43–8. Nyberg DA and V. L. Souter.(2001). Sonographic markers of fetal trisomies: second trimester. Journal of Ultrasound in Medicine; Vol 20, Issue 6 655-674. . Nyberg DA, Resta RG, Luthy DA, Hickok DE, Williams MA. (1993). Humerus and femur length shortening in the detection of Down syndrome. Am J Obstet Gynecol ;168:534–8 Nyberg DA, Resta RG, Lathy DA, Hickok DA, Mahony DS, Hirch JH. (1990). Prenatal sonographic findings of Down syndrome. Review of 94 cases. Obstet Gynecol ;76:370–7 MunimS,Khowaja .(2004) Effectiveness of Early Pregnancy Ultrasound in diagnosing Fetal abnormalities in High Risk Women. J Pak Med Assoc.; Nov;54(11):542-4. Odibo AO, Stamilio DM, Nelson DB, Sehdev HM, Macones GA..(2005). A cost-effectiveness analysis of prenatal screening strategies for Down syndrome. Obstet Gynecol. ;106(3):562-8. Perinatal Institute. (2005). Preg.info - Ultrasound Scan Information. Available from:[02 Dec. 2005]. RCOG. (1997). Report of the RCOG Working Party on Ultrasound Screening for Fetal Abnormalities. London. Spencer K, Carpenter P. (1993). Prospective study of prenatal screening for Down syndrome with free beta human chorionic gonadotrophin. BMJ ;307:764–9. Viora E, Errante G, Sciarrone A, Bastonero S, Masturzo B, Martiny G, Campogrande M.(2005). Fetal nasal bone and trisomy 21 in the second trimester.Prenat diagn: 25(6):511-5. Winter, Thomas, Stefanie B. Uhrich, Vivienne L. Souter, and David A. Nyberg. (2000). The "Genetic Sonogram": Comparison of the Index Scoring System with the Age-adjusted US Risk Assessment. Radiology. ;215:775-782 Whittle M.(1997). Ultrasonographic ‘soft markers’ of fetal Chromosomal defects. BMJ ;314:918 Woo, Joseph. (2005). Obstetric ultrasound. Ob-ultrasound .net. Available from: [27 Dec. 2005]. Ultrasound. (2005). The Harvey institute for human genetics (GMBS) Avaliable from< http://www.gmbc.org/genetics/ [NOV.27.2005] Van del Hof, Michael, and R. Douglas Wilson. (2005). Fetal Soft Markers in Obstetric Ultrasound. SOGC Clinical Practice Guidelines J Obstet Gynaecol Can. Jun; 27(6):592-636. Read More