NIPT Testing Time Frame
NIPT should be performed at 10 weeks gestation or later, when approximately 10-15% of total cell-free DNA in maternal plasma is of placental origin, providing sufficient fetal fraction for accurate analysis. 1
Optimal Testing Window
The standard time frame for NIPT is after 10 weeks gestation, as recommended by the American College of Radiology and the American College of Obstetricians and Gynecologists. 1
First trimester use (10-14 weeks) is the evidence-based application of NIPT, with detection rates for trisomy 21 of 99% and false positive rates of 0.5% in women who receive results. 1
NIPT can be performed as early as 9 weeks gestation, though fetal fraction may be lower at very early gestational ages, making the test less likely to provide a result. 1, 2
Why This Timing Matters
Before 9-10 weeks, insufficient fetal fraction is the primary limitation, as adequate placental-derived cell-free DNA must be present in maternal circulation for reliable analysis. 1, 2
If a "no-call" result occurs at 9 weeks, repeat testing at a slightly later gestational age provides a result in approximately 75-80% of cases. 1, 2
The minimum fetal fraction required is approximately 4%, and testing at 10 weeks or later optimizes the likelihood of achieving adequate fetal fraction. 2
Clinical Algorithm for Timing
For pregnancies presenting in first trimester (before 14 weeks): Offer NIPT at 10 weeks or later for optimal fetal fraction. 1
For pregnancies presenting in second or third trimester: NIPT is not the appropriate screening modality; standard anatomic ultrasound screening at 18-22 weeks is recommended for structural anomalies, and if aneuploidy screening is desired, proceed directly to diagnostic testing (amniocentesis) rather than screening. 1
Important Caveats
The primary value of NIPT is early reassurance or early diagnosis, allowing time for diagnostic confirmation and reproductive decision-making. 1
NIPT remains a screening test, not diagnostic, and all positive results require confirmation with chorionic villus sampling (CVS) or amniocentesis regardless of when performed. 1, 2
NIPT cannot replace ultrasound for detection of structural anomalies and does not screen for neural tube defects, making it complementary to, not a replacement for, anatomic ultrasound evaluation. 1
Maternal factors affecting test performance include obesity, which is associated with low fetal fraction and up to 20% test failure in high BMI women, making alternative screening methods potentially more appropriate for this population. 1, 2