Clinical Characteristics of 18-Trisomy Syndrome Failed to Be Diagnosed After Prenatal Screening
Summary
Objective: To discover the characteristics of trisomies 18 who were prenatal diagnosed or failed to be diagnosed, and to reduce the failed to be diagnosed.
Method: In this multicenter study, we collected a total of 52 babies of 18-trisomy syndrome (34 cases were prenatally diagnosed and 18 failed to be diagnosed) and analyzed their characteristics.
Results: In the past 13 years, according to the data from the prenatal diagnosis center in Jiangsu, the estimated detection rate was 65.4% for trisomies 18 in the second trimester. After analyzed the distribution of the groups according to T18-risk, there were two important cut-off values to be noted: 1/455 and 1/5050. It was worthwhile noting that the risk of 65.4% trisomy 18 cases was higher than 1/455, 90.4% higher than 1/5050. However, 96.1% cases in normal control group were lower than 1/5050. No case from normal control group would be higher than the value of risk in 1/450. Meanwhile, the T18-risk of 50% T18 failed to be diagnosed cases were 1/1001~1/5050. If we chose NIPT follow the standard of 1/5050, we could find 90.4 % T18 cases. It could increase 19.2% T18 babies be detected, but 3.2% normal mother would accept the NIPT examination which maybe unnecessary.
Conclusions: The prediction mode of HCG MoM and AFP MoM might be able to help us reduce the failed to be diagnosed. It is also necessary to adjust more reasonable range of NIPT with further clinical researches.
Keywords: 18 trisomy syndrome; Prenatal screening; Biomarkers; Prenatal diagnosis; Non-invasive prenatal testing
What Is Already Known on This Subject?
It is well known that prenatal screening and diagnosis is the effective way to avoid the birth of trisomy 18. However, there are still some cases will be missed.
What Do the Results of This Study Add?
There were two important cut-off value of prenatal screening to be noted: 1/455 and 1/5050. The T18-risk of 50% T18 failed to be diagnosed cases were 1/1001~1/5050. If we chose NIPT follow the standard of 1/5050, we can find 90.4 % T18 cases. It can increase 19.2% T18 babies be detected, while add 3.2% normal mother accepted the NIPT.
What are the Implications of These Study?
The prediction mode of HCG MoM and AFP MoM might be able to help us reduce the failed to be diagnosed. It is also necessary to adjust more reasonable range of NIPT with further clinical researches.
Introduction
Edwards syndrome, also named as 18-trisomy syndrome, is the common chromosomal abnormalities with an incidence of 1 in 3000~8000 in live births [1]. Due to an extra chromosome 18, the main clinical manifestations are multiple malformations and severe mental retardation, which caused only few children could survive the first year and very few cases could live longer [1,2]. According clinical researches, about 50% of babies with trisomy 18 could live longer than one week and about 5-10% of children beyond the first year [3]. So, it seriously affected the health of children. It is well known that the program of prenatal screening and diagnosis is the effective way to avoid the birth of trisomy 18 baby.
In the past three decades, prenatal screening for 18-trisomy syndrome has been widely used in pregnant women worldwide [4,5] which based on screening by maternal age, maternal serum markers screening, or detection of sonographic abnormalities (e.g., increased nuchal translucency thickness, growth retardation, choroid plexus cyst, overlapping of fingers, and congenital heart defects) [3]. The most common prenatal screening method for 18-trisomy syndrome is the serological prenatal screening in the second trimester, which detect the serum levels of free beta subunit of human chorionic gonadotropin (fβhCG) and alpha-fetoprotein (AFP) with maternal age [6,7]. The approximately detection rate was 57% with 0.7% false positive rate (Spencer K 1999). Effective screening can be carrying out in the first trimester screening (between 8 and 13 weeks), combination of serum levels of fβhCG, pregnancy-associated plasma protein A (PAPP-A), maternal age and ultrasound nuchal translucency (NT) measurements. The estimated detection rate was 87.0% for Down syndrome and 91.8% for 18-trisomy syndrome and trisomies 13 with the false-positive rate of 2.2% [9]. So, regardless of the kind of prenatal screening, it still had some cases of 18-trisomy syndrome would miss diagnosis because of the technical limitations of the prenatal screening.
Recently, non-invasive prenatal testing (NIPT), detection of fetal cell-free DNA (cfDNA) in maternal plasma, was proved to be a better prenatal screening program for common fetal aneuploidies. Nowadays, NIPT was widely used to prenatal screen the T21, T18, T13 [10]. Some societies and organizations , such as ACOG [11] and ISPD [12], have issued the committee opinions or guidelines about the clinical application of NIPT, and they both recommend the patients of high-risk group to accept NIPT. In 2015, Chinese scholars firstly suggested the mothers whose T18 screening results were intermediate risk (1/350~1/1000) to accept NIPT to reduce the failed to be diagnosed.
However, it is necessary to adjust more reasonable range of NIPT with further clinical researches.
In the present study, we have collected the cases of trisomies 18 who were prenatal diagnosed or failed to be diagnosed from the prenatal diagnosis center and analyzed their characteristics. With statistical analysis, we hope to be able to improve the programs of prenatal screening and reduce the failed to be diagnosed of 18-trisomy syndrome.
Materials and Methods
Patients and Design
The study design and protocol were reviewed and approved by the ethics committee of Changzhou Maternity and Child Health Care Hospital affiliated to Nanjing Medical University. From October 2002 to June 2015, the pregnant women received the prenatal screening in the hospital. A total of 52 babies of 18-trisomy syndrome were found in the center, included 34 cases were prenatally diagnosed and 18 cases failed to be diagnosed. We selected the objects of their mothers. Meanwhile, 309 mothers were selected as the normal control group. They accepted prenatal screening in our hospital and were confirmed have normal babies after followed-up. Both common characteristics were shown in Table 1.
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