fetal fraction
Percentage of cell-free fetal DNA in maternal blood plasma. Critical parameter for non-invasive prenatal testing accuracy and interpretation.
Full Definition
The proportion of cell-free DNA in maternal plasma that originates from the placenta and represents the fetal genetic material, typically comprising 3-13% of total circulating DNA after 10 weeks of gestation. Fetal fraction is a crucial quality metric for non-invasive prenatal testing (NIPT) as insufficient fetal DNA can lead to test failures or inaccurate results. Factors affecting fetal fraction include gestational age, maternal weight, maternal age, fetal aneuploidies (particularly trisomy 13 and 18), and twin pregnancies. Most laboratories require a minimum fetal fraction threshold of 4% for reliable NIPT results, with levels below this requiring repeat testing or alternative approaches.
Usage
Usage note: Always specify the percentage value when reporting fetal fraction in clinical contexts.
In Context
- "The NIPT result was reported as inconclusive due to low fetal fraction of 2.1% at 12 weeks gestation." — Laboratory report
- "Higher maternal BMI correlates with reduced fetal fraction and increased NIPT failure rates." — Clinical research study