RESUMO
BACKGROUND: Noninvasive genetic tests that use cell-free fetal DNA (cffDNA) are used increasingly in prenatal care. A low amount of cffDNA can have detrimental effects on the reliability of these tests. A marker to confirm the presence of fetal nucleic acids is therefore required that is universally applicable and easy to incorporate. METHODS: We developed a novel multiplex, single-tube, noninvasive fetal sex determination assay by combining amplification of AMELY cffDNA with one-step reverse transcription (RT)-PCR of trophoblast-derived cell-free RNA (cfRNA), which functions as a sex-independent fetoplacental marker. We tested plasma samples from 75 pregnant women in duplicate in a blinded fashion. The fetus was considered to be male in the case of a positive result for AMELY and cfRNA amplification in both RT-PCRs. The fetus was considered to be female in the case of negative AMELY and positive cfRNA result in both RT-PCRs. In other cases, the test was repeated. We compared the results with invasive prenatal testing and pregnancy outcomes. RESULTS: The AMELY cffDNA amplification and cfRNA result was unambiguous and identical in duplicate in 71 of 75 plasma samples (95%). Four samples (5%) required an extra replicate because of an absent fetoplacental marker. Thereafter, fetal sex was correctly determined in all 75 plasma samples. CONCLUSIONS: Amplification of trophoblast-derived cfRNA is a reliable marker for the confirmation of the presence of fetoplacentally derived nucleic acids in noninvasive fetal sex determination.
Assuntos
Amelogenina/sangue , DNA/sangue , Reação em Cadeia da Polimerase Multiplex/métodos , Diagnóstico Pré-Natal/métodos , RNA/sangue , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Análise para Determinação do Sexo/métodos , Adulto , Amelogenina/genética , Biomarcadores/sangue , DNA/genética , Feminino , Feto/irrigação sanguínea , Feto/metabolismo , Expressão Gênica , Humanos , Masculino , Reação em Cadeia da Polimerase Multiplex/normas , Placenta/irrigação sanguínea , Placenta/metabolismo , Gravidez , Diagnóstico Pré-Natal/normas , RNA/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa/normas , Sensibilidade e Especificidade , Análise para Determinação do Sexo/normasRESUMO
BACKGROUND: Implementation of non-invasive prenatal testing (NIPT) in Down syndrome screening programmes requires health policy decisions about its combination with other tests and its timing in pregnancy. AIM: Our aim was to aid health policy decision makers by conducting a quantitative analysis of different NIPT implementation strategies. METHODS: Decision trees were created to illustrate all plausible alternatives in a theoretical cohort of 100,000 pregnant women in five screening programmes: classical screening by the first-trimester combined test (FCT), pre-selection of high-risk women prior to NIPT by the FCT, NIPT as the first screening test at 10 weeks and at 13 weeks, and the simultaneous conductance of NIPT and the FCT. RESULTS: Pre-selection by FCT prior to NIPT reduces the number of amniocenteses to a minimum because of a reduction of false-positive NIPT results. If NIPT is the first screening test, it detects almost all fetal Down syndrome cases. NIPT at 10 weeks reassures women early in pregnancy, while NIPT at 13 weeks prevents unnecessary tests due to spontaneous miscarriages and allows for immediate confirmation by amniocentesis. CONCLUSION: Every implementation strategy has its advantages and disadvantages. The most favourable implementation strategy may be NIPT as the first screening test at 13 weeks, offering the most accurate screening test for Down syndrome, when the risk for spontaneous miscarriage has declined remarkably and timely confirmation by amniocentesis can be performed.