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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 1  |  Issue : 2  |  Page : 84-88

Cytogenetic analysis for fetal chromosomal abnormalities by amniocentesis: Review of over 40,000 consecutive cases in a single center


1 Shanghai Ji Ai Genetics and IVF Institute, Obstetrics and Gynecology Hospital, Fudan University, Shanghai 200011, China
2 Shanghai Ji Ai Genetics and IVF Institute, Obstetrics and Gynecology Hospital, Fudan University; Key Laboratory of Female Reproductive Endocrine Related Diseases, Obstetrics and Gynecology Hospital, Fudan University, Shanghai 200011, China

Date of Web Publication17-Oct-2017

Correspondence Address:
Yue-Ping Zhang
Shanghai Ji Ai Genetics and IVF Institute, Obstetrics and Gynecology Hospital, Fudan University, Shanghai 200011
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2096-2924.216865

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  Abstract 


Background: The aim of this study was to retrospectively investigate the 18-year experience of prenatal diagnosis of fetal karyotype analysis by amniocentesis.
Methods: In this study, the authors reviewed the cytogenetic results of 40,208 fetuses with indications for amniocentesis enrolled from December 1998 to December 2015. Cytogenetic analysis of amniotic fluid was performed in all these pregnancies. Eight indications for amniocentesis were included. The detection rate and distribution of abnormal karyotypes were observed in each indication.
Results: Among all these samples, abnormal maternal serum screening test was the most common indication for amniocentesis (17,536, 43.67%), followed by advanced maternal age (11,734, 29.18%), abnormal ultrasound findings (5,328, 13.25%), and required by pregnant women (2,557, 6.36%). Chromosomal abnormality was detected in 1,349 (3.36%) samples, 63.01% of the abnormalities were numerical, and 36.99% were structural. The detection rates of abnormal karyotype were 55.60% in one of the couple with chromosomal abnormality, 4.43% in the pregnant women with pathological ultrasound finding, 2.83% in the pregnant women with advanced age, and 2.73% in women with abnormal maternal serum screening tests. Of the fetuses with chromosome aberrations, 680 (50.41%) had trisomy 13, trisomy 18, or trisomy 21, and 138 (10.23%) had sex chromosome disorder. The other 531 abnormal samples included translocation, mosaicism, inversion, deletion, addition, and marker chromosome.
Conclusions: Cytogenetic analysis, therefore, remained an effective approach to decrease the birth defects of fetuses with indications for amniocentesis. These results could provide meaningful suggestions for clinical genetic consulting and prenatal diagnosis.

Keywords: Amniocentesis; Chromosomal Aberration; Cytogenetic; Genetic Consulting; Prenatal Diagnosis


How to cite this article:
Zhang S, Yin M, Xu JZ, Lei CX, Wu JP, Sun XX, Zhang YP. Cytogenetic analysis for fetal chromosomal abnormalities by amniocentesis: Review of over 40,000 consecutive cases in a single center. Reprod Dev Med 2017;1:84-8

How to cite this URL:
Zhang S, Yin M, Xu JZ, Lei CX, Wu JP, Sun XX, Zhang YP. Cytogenetic analysis for fetal chromosomal abnormalities by amniocentesis: Review of over 40,000 consecutive cases in a single center. Reprod Dev Med [serial online] 2017 [cited 2020 Jun 5];1:84-8. Available from: http://www.repdevmed.org/text.asp?2017/1/2/84/216865




  Introduction Top


Prenatal diagnosis by amniocentesis was introduced into clinical practice in the 1970s. For many years, cytogenetic analysis of amniotic fluid has remained the most common invasive diagnostic procedure for the detection of chromosomal aberrations in fetuses.[1] Conventional cytogenetic analysis allows for the identification of numerical and structural aberrations of the chromosomes, such as aneuploidies and translation. These aberrations were mainly caused by chromosomal nondisjunction or breakage during the anaphase of cell division.[2],[3]

The detection rates for abnormal karyotypes in fetuses with indications have been reported previously,[4],[5],[6],[7],[8],[9] while these publications had a small sample size. In this study, we analyzed the clinical indications and cytogenetic results of over 40,000 fetuses in our center and investigated the frequencies and distributions of abnormal karyotypes in different indications.


  Methods Top


In the study, prenatal samples were collected at the Shanghai Ji Ai Genetics and IVF Institute, Obstetrics and Gynecology Hospital of Fudan University from December 1998 to December 2015. A total of 40,268 cases were tested for a variety of indications, 60 samples were failed to culture, and the overall culture success rate was 99.85%. All cases included were for cytogenetic analyses from second-trimester by amniocentesis, amniotic fluid (15-20 mL) was collected under ultrasonic guidance. Each patient signed an informed consent before the procedure. Moreover, the data in these analyses presented here were gathered or generated during the process of clinically routine testing.

The indications for amniocentesis in this study included: (1) abnormal maternal serum screening results, (2) advanced maternal age, (3) pathological ultrasound findings, (4) having a history of abnormal gestation, (5) one of the couple with chromosomal abnormality, (6) exposed to teratogenic factors, (7) consanguineous marriage, and (8) required by pregnant women. Abnormal maternal serum screening results included pregnant women with high-risk screening results for trisomy 18 and 21. Advanced maternal age was defined as ≥35 years at delivery. Pathological ultrasound findings included fetal structural abnormalities and soft markers (such as duodenal atresia, increased nuchal fold thickness, choroid plexus cysts, and absent nasal bone). The group of having a history of abnormal neonatal included chromosomal abnormalities, neonatal death, and other medical conditions. Preimplantation genetic diagnosis (PGD) patients of balanced translocation were classified into the group of one of the couple with chromosomal abnormality. Teratogenic factors included X-ray, drugs, and virus infection in early pregnancy. Required by pregnant women included the maternal serum screening results below the risk of threshold, records not detailed and couples with mental retardation. For the cases with pathological ultrasound findings, although they had other indication(s), they were included into pathological ultrasound findings group.

Chromosome aberrations (numerical and structural) included aneuploidy, polyploidy, double aneuploidy, mosaicism, deletion, addition, inversion, translocation (balanced and unbalanced), ring chromosome, and marker chromosome.


  Results Top


Between 1998 and 2015, a total of 40,208 prenatal cases with indications were received for karyotype analysis in our laboratory. Cordocentesis samples were not included. The average maternal age at time of amniocentesis was 31.1 ± 4.2 years (range 17-47 years). Among these pregnancies, abnormal maternal serum screening test was the most common indication for amniocentesis (17,536, 43.67%), followed by advanced maternal age (11,734, 29.18%), abnormal ultrasound findings (5,328, 13.25%), and required by pregnant women (2,557, 6.36%). The indications of having a history of abnormal neonatal, one of the couple with chromosomal abnormality, exposed to teratogenic factors and consanguineous marriage were 2,108 (5.23%), 477 (1.19%), 442 (1.10%), and 31 (0.08%), respectively.

Of all fetuses, chromosomal abnormality was detected in 1,349 (3.36%) samples. The detection rates of abnormal karyotype were 55.60% (265/477) in the pregnant women of one of the couple with chromosomal abnormality, 4.43% (236/5,328) in the pregnant women with pathological ultrasound finding, 2.83% (332/11,734) in the pregnant women with advanced age, and 2.73% (479/17,536) in the women with abnormal maternal serum screening tests. In the indications of one of the couple with chromosomal abnormality, required by pregnant women and exposed to teratogenic factors, the detection rates were 0.67%, 0.78%, and 0.22%. No abnormal karyotype was found in the group of consanguineous marriage which was shown in [Table 1].
Table 1: The detection rates of abnormal karyotype in different indications

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In addition, of all the fetuses with chromosome abnormality, 680 (50.41%) had trisomy 21, trisomy 18, or trisomy 13 and 138 (10.23%) had sex chromosome disorders, which included Klinefelter syndrome, Turner syndrome, 47 XXX and 47 XYY. Furthermore, 278 had translocation (balanced and unbalanced), while 74.82% (208/278) were inherited from parent, the rate of de novo translocation was 25.18% (70/278). The remaining 253 cases (18.75%) included 9 with polyploidy, 4 with rare autosomal trisomy, 2 with double aneuploidy, 58 with inversion, 17 with deletion, 25 with addition, 5 with ring chromosome, 17 with marker chromosome, and 124 with mosaicism. Polymorphisms on chromosomes 1, 9, and 16 were excluded which were listed in [Table 2].
Table 2: The distribution of abnormal karyotype

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The distributions of abnormal karyotype in every indication were shown in [Table 3].
Table 3: The distributions of abnormal karyotype in each indication

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  Discussion Top


By now, karyotype analysis is still considered the gold standard for diagnosis of fetal chromosomal diseases. In our laboratory, a total of 40,208 patients were tested for a variety of indications between October 1998 and December 2015. The overall prevalence of chromosomal abnormalities in our study was 3.35%, which ranged from 0.22% to 55.60% in different indications [Table 1]. We confirmed that the fetuses with indications for amniocentesis carried a considerable risk for chromosomal abnormalities, especially in indications of one of the couple with chromosomal abnormality and pathological ultrasound findings. Cytogenetic analysis, therefore, is an important approach to decrease birth defects in prenatal diagnosis.

Some studies revealed that the incidence of chromosome abnormalities ranged from 2.90% to 8.24%.[4],[5],[6],[7],[8],[9] Our rate was consistent with the study of Han et al. which contained a large number of samples.[9] Positive maternal serum screening, advanced maternal age, and pathological ultrasound findings were always the most frequent indications, and these represented in our series 86.04% of the total indications. The highest detection rate of all indications was 55.60% (265/477) in fetuses of one of the couple with chromosomal abnormality, but all the abnormal karyotypes were inherited from parents. Moreover, 44 PGD patients of balanced translocation were enrolled in this group, 15 (34.09%) fetuses were the carriers of balanced translocation, and 29 (65.91%) fetuses were completely normal. If we excluded the cases (477) with indication of one of the couple with chromosomal abnormality, the overall detection rate will fall from 3.35% to 2.75%. The detection rate of advanced maternal age (2.83%) was similar to that of abnormal maternal serum screening tests (2.73%), which was a little lower than that of Han et al.[9] In addition, we did not find abnormal fetal karyotype in the indications of consanguineous marriage.

In the study of Han et al.[9] 61.20% of chromosomal abnormalities were numerical and 38.8% were structural. The most common chromosomal abnormality was trisomy 21. In our study, numerical and structural chromosomal abnormalities accounted for 63.01% and 36.99%, respectively. Moreover, the most commonly detected chromosome abnormalities were classical autosomal aneuploidies as expected, which represented 60.64%. Among them, trisomy 21 was the most common (37.44%). Of the sex chromosome aneuploidies, Klinefelter syndrome had the highest abnormal rate, and most of them (90.10%) were detected in the indications of advanced maternal age and abnormal maternal serum screening tests, while abnormal ultrasound finding was more sensitive to Turner syndrome. In addition, in the 278 identified translocation cases, 208 (74.82%) were inherited from parents; the de novo rate was 25.18% (70/278) in all translocation.

In 2008, Lo and Chiu identified Down's syndrome by detecting fetal-free DNA in maternal serum with noninvasive method successfully.[10] Several latest large sample studies indicated that noninvasive prenatal DNA testing could detect trisomy 21, 18, and 13, with a high sensitivity of up to 99.9%.[11],[12] While noninvasive prenatal DNA testing is limited to trisomy 21, 18, 13, and sex chromosome disorder in clinic recently, false positive and negative cannot be avoided.[13],[14] Thence, in our study, 531 abnormal cases (39.36%) including balanced translocation, mosaicism, polyploidy, inversion, and marker chromosome could not be detected accurately. Now, it is controversial about clinic diagnostic utility between conventional cytogenetic analysis and noninvasive prenatal DNA testing. In our reproductive center, we recommend amniocentesis for the pregnant women with indications. If pregnant women refuse invasive prenatal diagnosis, noninvasive prenatal DNA testing then is suggested.

Over the past 5 years, chromosomal microarray also has been increasingly used in cases of prenatal diagnosis, replacing or combining the cytogenetics analysis.[15],[16],[17] This would be expected to increase ~6% detection rate of chromosome abnormality by detecting microdeletions and microduplication in normal karyotype cases.[18],[19] It is likely that chromosomal microarray will become the routine method for karyotype analysis of pregnant women with indications for amniocentesis. However, balanced numerical aberrations such as translocation cannot be identified by microarray, which also have ~6.0% morbidity.[20],[21] Moreover, low mosaicism also cannot be detected accurately. Therefore, the combined use of cytogenetic analysis and chromosomal microarray may be the trend. In our center, we have already joined the two methods into prenatal diagnosis since 2013.

In summary, we present the large series of cytogenetic studies of amniotic fluid and our data confirm that cytogenetic analysis of amniotic fluid is an effective approach to detect fetal chromosome abnormalities. Obviously, there is a diverse range of chromosome abnormalities in fetuses with different indications. For fetuses with indications of high abnormal detection rate, karyotype analysis is supposed to be performed when undergoing genetic consulting and prenatal diagnosis. Moreover, for fetuses with the indications of low abnormal detection rate, either amniocentesis or noninvasive prenatal DNA testing was suggested.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2], [Table 3]


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