Detection of Fetal Chromosomal Anomalies

Date:  2021-03-06 05:29:15
5 pages  (1475 words)
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The purpose of study

To examine the percentage of fetal chromosomal anomalies that remained undetected as the first trimester combined testing is replaced with non-invasive prenatal testing trisomys 13, 18, and 21.

Method

Data on fetal karyotype, ultrasound measurement NT3.5mm were retrospectively collected from the cohort of 25 057 singleton pregnancies. The first trimester combined testing was performed. NT 3.5mm measurements were performed between 11 + 0 and 13+ 6 weeks of gestation Serum analysis of fb- HCG and PAPP- A and risk calculations was performed

Results and Discussions

Group I pregnancies ending in fetal demise (n = 18)-had a mean of 8.3mm Over half (10/18) of the fetuses in this group had Turner syndrome. Group II pregnancies with ultrasound anomalies (n = 36) had a mean NT thickness of 6.7mm. 23 pregnancies (61.0%), were terminated, this based on abnormal karyotype (8/23). In two cases (5.3%), postnatal array detected a chromosomal anomaly. 10 pregnancies (43.5%) resulted in the live births of an infant with a structural anomaly. For group III pregnancies with normal ultrasound findings (n =91) Mean of 4.5mm. One pregnancy had been lost to follow-up. This was after the invasive testing had reported a normal female karyotype. All the other pregnancies, (n = 90) resulted in live births. Also, a total of 83(91.2%) pregnancies, with a normal karyotype resulted in the birth of a healthy infant terminate pregnancy in 15 cases (44.1%).

Limitation of study women who did not opt for the follow-up of ultrasound invasive diagnosis, upon the detection of enlarged NT may not have been included women who had an NT 3.5mm at combined testing, subsequently opted for the invasive testing; are therefore likely to have a higher risk than those who refuse and could have introduced a small bias in our selected.

Role of the Second-Trimester Genetic Sonogram.'

Purpose of study To find out the role of second-trimester genetic sonogram for Down

Syndrome screen in the era of first-trimester screening and noninvasive prenatal testing

Method- Screening of individuals for detection of Down Syndrome (DS). The heterogeneity of study populations from which the screening efficiency of these markers was derived

Factors Affecting Accuracy of Screening in Genetic Sonogram.

The gestational age at the screening can affect both performances of individual markers and prevalence of DS, where some DS fetuses die with advancing gestation.

Maternal obesity largely affects the ability to visualize the sonographic markers for the DS screening results. "Completion rates of genetic sonogram are inversely related to maternal obesity; hence, obese women are under-screened."(Mujezinovic, 2007)

Also, individual cutoff level of risk used can affect the diagnostic performance of genetic sonogram methods

Impact of the First-Trimester Screening for DS on Genetic Sonogram

Calculation of the overall LR from a product of individual LR. Corresponding to presence or absence of the marker, the authors estimated that for a fixed 5% FPR, the genetic sonogram could improve detection rate for the DS of combined screening from 81% to 90%. That of integrated testing from 93% to 98%. Also women without DS and 12 cases of DS, who had integrated screening reported that use of cumulative LR of the second-trimester ultrasound markers derived from the literature reduced the FPR of the result from 3.6% to 2.9%.

Conclusion

Formulas derived from multivariate analyzes offer the most accurate means of calculating a modified risk for DS based on the genetic sonogram.

 

First-Trimester of Ductus Venosus, Nasal Bones, and the Down syndrome in a High-Risk Population.

The objective of study: Assessing the role of fetal ductus venosus and nasal bones evaluation in first-trimester screening for Down syndrome.

Method: Involved 628 consecutive fetuses were undergoing chorionic villus sampling. The indication for chorionic villus sampling was an increased risk for trisomy 21 based on maternal age. The nuchal translucency screening in 313 cases (54.7%), increased the maternal age in 195 (34.1%), and the other in 64 (11.2%). An ultrasound examination was performed before. The pattern of the blood flow in the ductus venosus and the presence or absence of the nasal bones was noted.

Results and discussion: An examination of both ductus venosus and nasal bones was satisfactory, in 572 fetuses. Among these, 497 (86.9%) reported a normal karyotype. 47 (8.2%) of this were affected with Down syndrome. The (LR), likelihood ratio for the trisomy 21 was 7.05, (95%, confidence interval of 4.2711.64). The case of abnormal ductus venosus that flow and 6.42 (95% confidence interval 3.86 10.67) in the case of absent nasal bones. Increased fetal nuchal translucency, Down syndrome is significantly associated with first-trimester abnormal flow velocity patterns in the ductus venosus and the hypoplasia of the nasal bones. (Obstet Gynecol 2005) Of Obstetricians and Gynecologists. The indication for CVS was hence an increased risk increased maternal age in 195 (34.1%), and other in 64 (11.2%).

Conclusion: with increased fetal nuchal translucency, Down syndrome is hence significantly associated with the first-trimester abnormal flow of velocity patterns in the ductus venosus and hypoplasia of the nasal bones. (Obstet Gynecol)

 

Screening for Down Syndrome Based on the Maternal Age

The objective of study- To examine the performance of the screening for Down syndrome based on the maternal age, the fetal nuchal translucency (NT) and the different combinations of additional ultrasound parameters. The nasal bone (NB), tricuspid flow (TF) and the ductus venosus (DV).

Method -Identified 1916 pregnant women who underwent chorionic villous sampling between 2008 and 2014. Before invasive testing, the crown-rump length, NT, the NB, TF, and the DV were measured. Added value of additional markers NB, TF, and DV, were then compared with the screenings based on trisomy 21 on maternal age (MA) and NT thickness alone

Results and discussion- 1823 fetuses had a normal karyotype, and 93 fetuses had trisomy 21. In 62.3% of the cases. In a normal population, the NB, the TF and the DV were abnormal with 36, (2.0%), 31, (1.7%) and 64, (3.5%) of the cases, respectively. In trisomic population, the findings were abnormal in 57 (61.3%), 57 (61.3%) and 56 (60.2%) of cases, respectively. In 108 (5.9%) of normal and 89 (95.7%) of the trisomic fetuses, at least one of the markers was abnormal.

The highest detection rate could be achieved if the addition to MA and fetal NT, all the three other sonographic markers NB, TF and DV is assessed.

Limitations of study- the study examined a high-risk population that was referred because of increased MA or increased NT. The risk calculation did not take into account the fact that NB, TF, and DV are not entirely independent.

First-trimester contingent screening for trisomies 21, 18 and13 by fetal nuchal translucency and ductus venosus flow and maternal blood cell-free DNA testing

The objective of study- To examine the performance of screening of major trisomies. Applies the policy of first-line assessment of the risk according to maternal age, the fetal nuchal translucency thickness (NT) and the ductus venosus pulsatility index for veins. (DV-PIV) This is finally accompanied by cell-free DNA (cfDNA) testing in pregnancies at levels of intermediate risk.

Method - The distribution of risks was estimated based on maternal age, fetal NT and DV-PIV in a population of 86 917 unaffected and 491 trisomic pregnancies undergoing prospective screening for trisomies.

Results and discussions- Screening for trisomies 21, 18 and 13 can detect approximately 96%, 95% and 91% of the cases, respectively. The false-positive rate (FPR) being 0.8%. The assumption of the costs of ultrasound screening, the cfDNA testing and that of invasive testing are 150, 500 and 1000, respectively, and then the overall cost of such a policy would be approximate to 250 per patient. The alternative policy, of the universal screening by cfDNA testing, can potentially detect up to 99%, 97% and 92% of the cases. The overall cost is 500 more per patient.

Limitations of study- It is susceptible to operator bias due to the very high positive- or negative likelihood ratios, from previous classification. The use of DV-PIV5has helped overcome this problem, thereby reducing the risk of bias.

Conclusion-Incorporation of cfDNA test into a contingent policy of early screening for the trisomies, based on the risk derived from first-line screening according to a combination of maternal age. (Bianchi, 2014). The fetal NT and DV-PIV, can then potentially detect a high proportion of affected cases.

References

Kagan KO, Wright D, Baker A, Sahota D, Nicolaides KH(2008). Screening for trisomy 21 by maternal age, fetal nuchal translucency thickness, free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A. Ultrasound Obstet Gynecol.

This book shows how cfdna testing into a Contingent policy of early screening for the major Trisomies, based on the risk derived from first-line. It highlights the major issues affecting the issue screening for trisomy.

ACOG Committee (2004) First-trimester screening for fetal aneuploidy. Obstet Gynecol

This book explains how First-Trimester Ductus Venosus, Nasal Bones, and

Down syndrome is high-risk in certain populations.

Bianchi DW, Oepkes D, Ghidini A (2014.).Noninvasive DNA testing be the Standard Screening

Test for Down syndrome in women.

It evaluates First trimester ultrasound screening for Down syndrome based

on maternal age, fetal nuchal translucency and different combinations of the additional markers nasal bone, tricuspid and ductus venosus flow.

Benacerraf BR, Frigoletto FD Jr, Laboda LA (1985). Sonographic diagnosis of Down syndrome in the second trimester. Am J Obstet Gynecol

It explains the role of the second-trimester for Down syndrome screen in the era of first-trimester screening and noninvasive prenatal testing.

Mujezinovic F, Alfirevic (2007). Procedure-related complications of amniocentesis and chorionic villous sampling: a systematic review. Obstet Gynecol.

It explains how to detect fetal chromosomal anomalies and shows how nuchal translucency measurement have added value in the era of non-invasive prenatal testing.

 

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