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Falsos Positivos e Falsos Negativos dos NIPT (ADN fetal livre) em grávidas do CHUCB
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Authors
Abstract(s)
Introdução: O diagnóstico pré-natal é essencial para a deteção precoce de
aneuploidias fetais, como as cromossomopatias mais frequentes (trissomias 21, 18 e
13), permitindo decisões informadas. O rastreio combinado do primeiro trimestre e os
testes invasivos, como a BVC e a amniocentese, têm sido amplamente utilizados, mas
apresentam limitações e riscos. O teste pré-natal não invasivo, realizado no CHUCB
desde 2016, analisa o ADN fetal livre no sangue materno, oferecendo alta sensibilidade
e reduzindo a necessidade de testes invasivos. A crescente utilização do NIPT reforça a
importância de avaliar a sua precisão e impacto clínico.
Objetivos: Este estudo visa avaliar a ocorrência de falsos positivos e falsos negativos
nos NIPT realizados no CHUCB, comparando-os com o cariótipo fetal e o
fenótipo/genótipo à nascença. Para além disso, pretende identificar fatores associados
a resultados incorretos e propor estratégias para otimizar o aconselhamento genético e
a prática clínica no rastreio pré-natal.
Materiais e métodos: O estudo é observacional, transversal e retrospetivo, baseado
na análise de registos clínicos de grávidas seguidas nas consultas de diagnóstico prénatal e obstetrícia no Serviço de Obstetrícia do CHUCB entre fevereiro de 2016 e junho
de 2024. Foram incluídas 296 gestações e 296 NIPT válidos, após aplicação de critérios
de exclusão. Os dados foram recolhidos de forma anónima e incluíram variáveis
demográficas, gestacionais, resultados do NIPT e de outros métodos de rastreio e
diagnóstico pré-natal. A análise estatística foi realizada com Microsoft Excel 365 e IBM
SPSS 29.0.1.1. O estudo foi aprovado pela Comissão de Ética para a Saúde e pelo
Conselho de Administração do CHUCB, garantindo a confidencialidade dos dados.
Resultados: A amostra incluiu 296 gestações com idade materna média de 37 anos. A
maioria das conceções foi espontânea (82,1%). Predominaram gestações únicas
(96,3%), totalizando 307 fetos, distribuídos equitativamente entre os sexos. O NIPT
identificou baixa probabilidade de aneuploidia em 97,6% dos casos, com 7 resultados
de alta probabilidade de aneuploidias, dos quais 6 foram confirmados e 1 revelou ser
falso positivo. Não foram registados falsos negativos para as aneuploidias rastreadas,
porém 2 fetos com aneuploidia não foram identificados pelo NIPT, visto que este
apenas rastreava as três aneuploidias mais frequentes, a trissomia 21, trissomia 18 e
trissomia 13. Assim, o NIPT apresentou sensibilidade de 100% e especificidade de 99,65%. A associação entre os resultados do NIPT e a presença de aneuploidia foi
estatisticamente significativa (p<0,001).
Conclusão: O NIPT demonstrou elevado desempenho na deteção de aneuploidias
fetais na amostra estudada, com sensibilidade de 100%, especificidade de 99,65% e
uma taxa de falsos positivos de apenas 0,3%, sem falsos negativos registados.
Comparado ao RCPT, mostrou-se significativamente superior na redução de falsos
positivos. No entanto, reforça-se que o NIPT é um teste de rastreio e não de
diagnóstico, sendo essencial confirmar resultados positivos com métodos invasivos. A
escolha do painel de rastreio deve ser ajustada ao perfil de risco da gestante, e o
aconselhamento genético adequado é fundamental para decisões informadas. Apesar
do alto desempenho, a ocorrência de resultados incorretos ainda representa um
desafio, destacando a necessidade de um uso criterioso e integrado do NIPT na prática
clínica.
Introduction: Prenatal diagnosis is essential for the early detection of fetal aneuploidies, such as the most common chromosomal abnormalities (trisomies 21, 18, and 13), allowing for informed decision-making. First-trimester combined screening and invasive tests, such as CVS and amniocentesis, have been widely used but present limitations and risks. The non-invasive prenatal test (NIPT), implemented at CHUCB since 2016, analyzes free fetal DNA in maternal blood, offering high sensitivity and reducing the need for invasive tests. The growing use of NIPT emphasizes the importance of evaluating its accuracy and clinical impact. Objectives: This study aims to evaluate the occurrence of false positives and false negatives in NIPTs performed at CHUCB, comparing them with fetal karyotype and phenotype/genotype at birth. Furthermore, it seeks to identify factors associated with incorrect results and propose strategies to optimize genetic counseling and clinical practice in prenatal screening. Materials and Methods: The study is observational, cross-sectional, and retrospective, based on the analysis of clinical records of pregnant women followed at the prenatal diagnosis and obstetrics consultations of the CHUCB Obstetrics Service between February 2016 and June 2024. A total of 296 pregnancies and 296 valid NIPTs were included after applying exclusion criteria. Data were collected anonymously and included demographic, gestational variables, NIPT results, and results from other prenatal screening and diagnostic methods. Statistical analysis was performed using Microsoft Excel 365 and IBM SPSS 29.0.1.1. The study was approved by the Health Ethics Committee and the CHUCB Board of Directors, ensuring data confidentiality. Results: The sample included 296 pregnancies with an average maternal age of 37 years. Most conceptions were spontaneous (82.1%). Single pregnancies predominated (96.3%), totaling 307 fetuses, evenly distributed by sex. NIPT identified a low probability of aneuploidy in 97.6% of cases, with 7 high-probability results for aneuploidy, of which 6 were confirmed, and 1 was a false positive. No false negatives were recorded for the screened aneuploidies; however, 2 fetuses with aneuploidy were not identified by NIPT, as it only screened the three most common aneuploidies: trisomy 21, trisomy 18, and trisomy 13. Thus, NIPT showed 100% sensitivity and 99.65% specificity. The association between NIPT results and the presence of aneuploidy was statistically significant (p<0.001). Conclusion: NIPT demonstrated high performance in detecting fetal aneuploidies in the studied sample, with 100% sensitivity, 99.65% specificity, and a false positive rate of only 0.3%, with no false negatives recorded. Compared to the RCPT, it was significantly superior in reducing false positives. However, it is emphasized that NIPT is a screening test and not a diagnostic test, and positive results must be confirmed with invasive methods. The choice of the screening panel should be adjusted to the pregnant woman's risk profile, and appropriate genetic counseling is crucial for informed decision-making. Despite its high performance, the occurrence of incorrect results still represents a challenge, highlighting the need for careful and integrated use of NIPT in clinical practice.
Introduction: Prenatal diagnosis is essential for the early detection of fetal aneuploidies, such as the most common chromosomal abnormalities (trisomies 21, 18, and 13), allowing for informed decision-making. First-trimester combined screening and invasive tests, such as CVS and amniocentesis, have been widely used but present limitations and risks. The non-invasive prenatal test (NIPT), implemented at CHUCB since 2016, analyzes free fetal DNA in maternal blood, offering high sensitivity and reducing the need for invasive tests. The growing use of NIPT emphasizes the importance of evaluating its accuracy and clinical impact. Objectives: This study aims to evaluate the occurrence of false positives and false negatives in NIPTs performed at CHUCB, comparing them with fetal karyotype and phenotype/genotype at birth. Furthermore, it seeks to identify factors associated with incorrect results and propose strategies to optimize genetic counseling and clinical practice in prenatal screening. Materials and Methods: The study is observational, cross-sectional, and retrospective, based on the analysis of clinical records of pregnant women followed at the prenatal diagnosis and obstetrics consultations of the CHUCB Obstetrics Service between February 2016 and June 2024. A total of 296 pregnancies and 296 valid NIPTs were included after applying exclusion criteria. Data were collected anonymously and included demographic, gestational variables, NIPT results, and results from other prenatal screening and diagnostic methods. Statistical analysis was performed using Microsoft Excel 365 and IBM SPSS 29.0.1.1. The study was approved by the Health Ethics Committee and the CHUCB Board of Directors, ensuring data confidentiality. Results: The sample included 296 pregnancies with an average maternal age of 37 years. Most conceptions were spontaneous (82.1%). Single pregnancies predominated (96.3%), totaling 307 fetuses, evenly distributed by sex. NIPT identified a low probability of aneuploidy in 97.6% of cases, with 7 high-probability results for aneuploidy, of which 6 were confirmed, and 1 was a false positive. No false negatives were recorded for the screened aneuploidies; however, 2 fetuses with aneuploidy were not identified by NIPT, as it only screened the three most common aneuploidies: trisomy 21, trisomy 18, and trisomy 13. Thus, NIPT showed 100% sensitivity and 99.65% specificity. The association between NIPT results and the presence of aneuploidy was statistically significant (p<0.001). Conclusion: NIPT demonstrated high performance in detecting fetal aneuploidies in the studied sample, with 100% sensitivity, 99.65% specificity, and a false positive rate of only 0.3%, with no false negatives recorded. Compared to the RCPT, it was significantly superior in reducing false positives. However, it is emphasized that NIPT is a screening test and not a diagnostic test, and positive results must be confirmed with invasive methods. The choice of the screening panel should be adjusted to the pregnant woman's risk profile, and appropriate genetic counseling is crucial for informed decision-making. Despite its high performance, the occurrence of incorrect results still represents a challenge, highlighting the need for careful and integrated use of NIPT in clinical practice.
Description
Keywords
Adn Fetal Livre Aneuploidias Falso Negativo Falso Positivo Teste Pré-Natal Não Invasivo