What is the fetal fraction?

NIPS analyzes fetal DNA in the mother’s blood. The amount of fetal DNA in the samples is known as the fetal fraction. NIPS is only accurate at or after 10 weeks gestation because this is when there is a high enough fetal fraction to do the analysis. If the test cannot detect enough fetal material, a non-reportable result will be issued. This is also known as a low fetal fraction. Non-reportable results and results with low fetal fractions (below 3%) have been associated with a higher risk for a chromosome condition in that pregnancy. Women with these results should consider meeting with a genetic counselor to discuss the option of further screening (like a level II ultrasound) or repeating their NIPS later in pregnancy?