From the Guidelines
Fetal fraction is a crucial parameter in non-invasive prenatal testing (NIPT) that represents the proportion of cell-free DNA in maternal blood originating from the placenta, and its significance lies in its impact on test accuracy and failure rates, as evidenced by studies such as 1. The fetal fraction is essential for interpreting NIPT results, as a minimum threshold is required for reliable testing. According to 1, the chance of test failure due to low fetal fraction varies and is reported to be between 0.9-8.1%. Key factors influencing fetal fraction include:
- Gestational age, with lower fractions at earlier gestations
- Maternal conditions, which can affect the amount of cell-free DNA
- Certain fetal chromosomal abnormalities, such as trisomy 13,18, or triploidy, which may be associated with lower fetal fractions Understanding the significance of fetal fraction helps healthcare providers counsel patients appropriately, especially in cases of test failure or inconclusive results, and guides the decision to offer alternative diagnostic testing options, as suggested by 1. In cases where NIPT results are ambiguous or the test fails, alternative diagnostic approaches like amniocentesis or chorionic villus sampling may be recommended for patients with persistently low fetal fraction, as these methods can provide definitive genetic information about the fetus.
From the Research
Definition of Fetal Fraction
- Fetal fraction refers to the proportion of cell-free fetal DNA (cffDNA) in the mother's blood that is of fetal origin 2.
- It is an important factor in non-invasive prenatal testing (NIPT) as it affects the accuracy of the test results 2, 3.
Significance of Fetal Fraction in NIPT
- A higher fetal fraction is generally associated with more accurate NIPT results 2, 3.
- A minimum fetal fraction of 4% is often considered necessary for reliable NIPT results 3.
- Factors that can affect fetal fraction include gestational age, maternal body mass index (BMI), and placental biomarkers 2, 3.
Factors Affecting Fetal Fraction
- Gestational age: Fetal fraction tends to increase with gestational age 2, 3.
- Maternal BMI: Fetal fraction tends to decrease with increasing maternal BMI 2.
- Placental biomarkers: Fetal fraction is associated with certain placental biomarkers, such as free β-hCG, PAPP-A, and PlGF 2.