Detection rates and residual risk for a postnatal diagnosis of an atypical chromosome aberration following combined first-trimester screening

Current Perspectives of Prenatal Cell-free DNA Screening in Clinical Management of First-Trimester Septated Cystic Hygroma

First-trimester septated cystic hygroma occurs in approximately 1 in 268 pregnancies and has long been associated with a markedly increased risk of fetal aneuploidy and, among euploid fetuses, an increased risk of structural anomalies primarily affecting the cardiac and skeletal systems. Invasive prenatal diagnosis – chorionic villus sampling and/or amniocentesis – encompasses the time-honored clinical tools for the next step in management following prenatal sonographic diagnosis of first-trimester septated cystic hygroma. Currently, prenatal cell-free DNA (cfDNA) screening for fetal aneuploidy with select microdeletions is gradually replacing the considerably less sensitive, and labor-intensive combined first-trimester screening. These new technologies have opened potential new venues in the clinical management of this ominous late first-trimester sonographic diagnosis. Advances in cfDNA technologies are now permitting detection of chromosomal copy number variants (CNV) larger than 7Mb across genome and select serious single-gene disorders (mainly impacting skeletal and neurological development), affecting quality of life and may benefit from medical and/or surgical management. This commentary will address the available non-invasive prenatal screening technologies, which clearly enhance immediate genetic analysis modalities applicable in the presence of the complex sonographic finding of first-trimester septated cystic hygroma.

SIGNIFICANCE OF LOW MATERNAL SERUM Β-HCG LEVELS IN THE ASSESSMENT OF THE RISK OF ATYPICAL CHROMOSOMAL ABNORMALITIES

INTRODUCTION

The introduction of prenatal cell-free DNA as a screening test has surpassed traditional combined first-trimester screening (cFTS) in the detection of common trisomies. However, its current limitation in detecting only common trisomies is affecting the diagnostic yield for other clinically significant chromosomal abnormalities.

METHODS

In efforts to optimize the detection of fetuses with genetic abnormalities, we have analyzed the relationship between the cFTS risk score and biomarkers with atypical chromosomal abnormalities. Furthermore, we have evaluated the impact of prenatal cell-free DNA screening on the detection of chromosomal abnormalities in our population. For these purposes, we performed a retrospective study of 877 singleton pregnancies who underwent chromosomal microarray analysis (CMA) between 2013 to 2020 and for whom first-trimester screening data were available.

RESULTS

The results demonstrated that low levels of free beta human chorionic gonadotropin (β-hCG) (≤ 0.37 MoM) and increased fetal nuchal translucency (NT) (≥ 3.5mm) were statistically associated with the presence of atypical chromosomal abnormalities. In fact, the risk of pathogenic CMA results increased from 6% to 10% when fetal NT was increased and from 6% to 20% when a low serum β-hCG level was detected in the high-risk cFTS group. Moreover, our results showed that altered serum levels of β-hCG can have a substantial impact on the early detection of clinically relevant copy number variants.

DISCUSSION/CONCLUSION

Traditional cFTS can potentially identify a substantial proportion of atypical chromosomal aberrations, and women with increased NT or low maternal serum β-hCG levels are at increased risk of having pathogenic CMA results. Our results may help clinicians and women decide whether invasive testing or prenatal cell-free DNA screening testing are more appropriate for each situation.

Chances and Challenges of New Genetic Screening Technologies (NIPT) in Prenatal Medicine from a Clinical Perspective: A Narrative Review

In 1959, 63 years after the death of John Langdon Down, Jérôme Lejeune discovered trisomy 21 as the genetic reason for Down syndrome. Screening for Down syndrome has been applied since the 1960s by using maternal age as the risk parameter. Since then, several advances have been made. First trimester screening, combining maternal age, maternal serum parameters and ultrasound findings, emerged in the 1990s with a detection rate (DR) of around 90-95% and a false positive rate (FPR) of around 5%, also looking for trisomy 13 and 18. With the development of high-resolution ultrasound, around 50% of fetal anomalies are now detected in the first trimester. Non-invasive prenatal testing (NIPT) for trisomy 21, 13 and 18 is a highly efficient screening method and has been applied as a first-line or a contingent screening approach all over the world since 2012, in some countries without a systematic screening program. Concomitant with the rise in technology, the possibility of screening for other genetic conditions by analysis of cfDNA, such as sex chromosome anomalies (SCAs), rare autosomal anomalies (RATs) and microdeletions and duplications, is offered by different providers to an often not preselected population of pregnant women. Most of the research in the field is done by commercial providers, and some of the tests are on the market without validated data on test performance. This raises difficulties in the counseling process and makes it nearly impossible to obtain informed consent. In parallel with the advent of new screening technologies, an expansion of diagnostic methods has begun to be applied after invasive procedures. The karyotype has been the gold standard for decades. Chromosomal microarrays (CMAs) able to detect deletions and duplications on a submicroscopic level have replaced the conventional karyotyping in many countries. Sequencing methods such as whole exome sequencing (WES) and whole genome sequencing (WGS) tremendously amplify the diagnostic yield in fetuses with ultrasound anomalies.

National data on the early clinical use of non-invasive prenatal testing in public and private healthcare in Denmark 2013-2017

INTRODUCTION

In Denmark, non-invasive prenatal testing (NIPT) has been used since 2013. We aimed to evaluate the early clinical use of NIPT in Danish public and private healthcare settings before NIPT became an integrated part of the national guidelines on prenatal screening and diagnosis in 2017.

MATERIAL AND METHODS

NIPT data were collected between March 2013 and June 2017 from national public registries and private providers. Results from follow-up samples (chorionic villi, amniotic fluid, postnatal blood or fetal tissue) were included from The Danish Cytogenetics Central Registry and indications and outcome from The Danish Fetal Medicine Database.

RESULTS

A total of 3936 NIPT results were included in the study from public hospitals (n = 3463, 88.0%) and private clinics (n = 473, 12.0%). The total number of prenatal tests was 19 713 during the study period: 20% were NIPT analyses (n = 3936) and 80% invasive procedures (n = 15 777). Twenty-five percent of NIPTs in the private clinics were performed before gestational week 11⁺⁰ , whereas NIPT in public settings was used only after combined first trimester screening (P < .001). Regardless of indication, the national public sensitivity was 96.9% (95% CI 82.0%-99.8%) for trisomy 21, 100% (95% CI 46.3%-100%) for trisomy 18, 100% (95% CI 5.5%-100%) for trisomy 13, and 87.0% (95% CI 74.5%-92.4%) for any fetal chromosomal aberration. Forty-seven true-positive NIPT results included cases of common aneuplodies (trisomy 21, n = 31; trisomy 18, n = 5; and trisomy 13, n = 1), sex chromosomal aberrations (n = 7) and atypical chromosomal aberrations (n = 3). One false-negative NIPT result occurred (trisomy 21). Of 47 cases, 21 (45%) cases with a true-positive NIPT result resulted in live births by choice; 11 of these children had Down and 4 had Edwards syndrome.

CONCLUSIONS

The total number of NIPT analyses was low compared with the number of invasive procedures in the implementation period. In contrast to the generally high termination rate after a positive result following invasive testing in Denmark, a high proportion of true-positive NIPT results from the public setting resulted in live births. NIPT may be an important risk-free alternative to invasive testing for a minority of women in the public setting who wish to use prenatal genetic testing for information only and not for reproductive decision-making.

Application value of NIPT for uncommon fetal chromosomal abnormalities

Objective

To investigate the clinical value of noninvasive prenatal testing (NIPT) for fetal chromosomal deletion, duplication, and sex chromosome abnormalities.

Methods

The study included 6239 pregnant women with singletons in the first and second trimester of pregnancy who received NIPT from December 2017 to June 2019. For pregnant women at high risk of deletion, duplication, and sex chromosome abnormalities indicated by NIPT, amniocentesis was recommended for karyotype analysis and chromosome copy number variation detection to verify the NIPT results and analyze chromosome abnormalities. Women at low risk and with no other abnormal results continued with their pregnancies.

Results

Among the 6239 pregnant women who received NIPT, there were 15 cases of chromosomal deletion (12 cases confirmed by amniocentesis), 16 cases of chromosomal duplication (9 cases confirmed by amniocentesis), and 17 cases of sex chromosome abnormalities (11 cases confirmed by amniocentesis). Of these cases, 32 were finally confirmed by amniotic fluid cell karyotype analysis. The coincidence rate was 66.7% (32/48). There were no abnormalities found for the remaining low risk pregnant women during follow-up.

Conclusion

NIPT has good application value in predicting fetal chromosomal deletion, duplication, and sex chromosome abnormalities. It can improve the detection rate of fetal chromosomal abnormalities, but further prenatal diagnosis is needed.