From the Guidelines
Yes, both Combined First Trimester Screening (CFTS) and Non-Invasive Prenatal Testing (NIPT) can be performed in twin pregnancies, though with some important considerations. CFTS in twins includes maternal serum markers (PAPP-A and free β-hCG) along with nuchal translucency ultrasound measurements for each fetus, providing individual risk assessments for chromosomal abnormalities like Down syndrome. However, CFTS has lower detection rates and higher false positive rates in twins compared to singleton pregnancies. NIPT can also be used in twin pregnancies by analyzing cell-free DNA in maternal blood, with high sensitivity for detecting trisomies 21,18, and 13, as recommended by the American College of Medical Genetics and Genomics (ACMG) in their 2023 guideline 1. NIPT performs better in identical (monozygotic) twins than in fraternal (dizygotic) twins because the latter have different genetic profiles. For twin pregnancies, it's essential to note that while these screening tests can provide risk assessment, they cannot distinguish which fetus might be affected if an abnormality is detected. In such cases, diagnostic testing like amniocentesis or chorionic villus sampling would be needed for confirmation, though these carry a small risk of pregnancy loss, highlighting the importance of careful counseling and consideration of the benefits and limitations of these tests, as emphasized in the ACMG guideline 1. The use of NIPT in twin pregnancies has been supported by recent studies, which have shown its effectiveness in reducing the need for invasive diagnostic testing, thereby minimizing the risk of pregnancy loss 1. Key considerations for healthcare providers include the need for thorough counseling, education, and standardized training on the benefits and limitations of NIPT, as well as the importance of addressing potential harms and the psychosocial impact of screening results 1. Overall, the decision to perform CFTS and NIPT in twin pregnancies should be made on a case-by-case basis, taking into account the individual patient's risk factors, medical history, and personal preferences, with careful consideration of the potential benefits and limitations of these tests, as supported by the most recent and highest-quality evidence 1.
From the Research
CFTS and NIPT in Twins
- CFTS (Combined First Trimester Screening) and NIPT (Non-Invasive Prenatal Testing) are screening tests used to detect fetal chromosomal abnormalities.
- According to 2, NIPT is an important addition to the range of screening tests for fetal chromosomal abnormalities and is superior to other screening modalities for trisomy 21.
- However, there is limited information on the use of CFTS and NIPT in twins, as most studies focus on singleton pregnancies.
- 3 discusses the use of cell-free DNA screening for fetal aneuploidy, but does not specifically address its use in twin pregnancies.
- 4 mentions the use of cell-free fetal DNA (cffDNA) in screening for trisomy 21, but does not provide information on its use in twin pregnancies.
Limitations and Complexities
- NIPT has limitations and complexities that requesting clinicians and their patients should understand, as noted in 2.
- The performance characteristics of NIPT and existing screening tests are compared in 2, but the study does not address the use of these tests in twin pregnancies.
- 5 discusses the diagnostic testing after positive results on cell-free DNA screening, but does not specifically address twin pregnancies.
- 6 evaluates the clinical outcome of non-invasive prenatal testing (NIPT) results positive for rare autosomal aneuploidies and large copy number variations, but does not provide information on its use in twin pregnancies.
Clinical Use and Limitations
- The clinical use of NIPT is discussed in 2, but the study does not address its use in twin pregnancies.
- 3 notes that cell-free DNA screening does not replace the precision obtained with diagnostic tests, such as chorionic villus sampling or amniocentesis, and is limited in its ability to identify all chromosome abnormalities.
- The limitations of cell-free DNA screening performance are discussed in 3, but the study does not address the use of these tests in twin pregnancies.