Harmony Prenatal Test After 13 Weeks
Yes, a patient can get the Harmony prenatal test after 13 weeks of gestation, as cell-free DNA testing can be performed throughout pregnancy and is not restricted to the first trimester. 1, 2
Optimal Timing Considerations
The Harmony test (a cell-free DNA/NIPT platform) can technically be performed from 10 weeks gestation onward without an upper gestational age limit. 1, 2 However, the timing of testing involves several practical considerations:
Performance Characteristics by Gestational Age
Cell-free DNA testing maintains high accuracy throughout pregnancy, with detection rates for trisomy 21 exceeding 99% in singleton pregnancies regardless of when the sample is drawn after 10 weeks. 3, 2
First-trimester biochemical screening (PAPP-A, free β-hCG) performs optimally between 11-13 weeks, with sensitivity declining after 13 completed weeks for combined first-trimester screening approaches. 4 This is relevant only if combining NIPT with traditional screening, not for NIPT alone.
The Harmony test specifically has been validated from 10 weeks gestation, with the initial study reporting results obtained in 94.8% of twin pregnancies tested during the 10-14 week window. 3
Practical Advantages of Testing After 13 Weeks
Lower spontaneous miscarriage risk: Testing at 13 weeks or later avoids performing screening on pregnancies that would have miscarried naturally, reducing unnecessary anxiety and follow-up testing. 5
Immediate diagnostic confirmation available: After 15 weeks, amniocentesis becomes the standard diagnostic option if NIPT results are high-risk, allowing for streamlined follow-up without the need for chorionic villus sampling (which is typically performed between 10-13 weeks 6 days). 4, 5
Higher fetal fraction: As pregnancy advances, the fetal fraction in maternal blood generally increases, potentially reducing the "no-call" rate due to insufficient fetal fraction. 6
Important Caveats
Test Failure and Redraw Considerations
Maternal weight significantly impacts test success: Higher maternal weight decreases the odds of obtaining a result (OR 0.988 per kg), which is particularly relevant for samples drawn at any gestational age. 6
If initial testing fails due to insufficient fetal fraction, waiting longer between draws increases success rates (OR 1.040 per day of interval), but this must be balanced against advancing gestational age and clinical urgency. 6
Screening vs. Diagnostic Testing
NIPT is a screening test, not diagnostic: Regardless of gestational age at testing, positive results require confirmation with diagnostic testing (amniocentesis after 15 weeks) before making irreversible pregnancy management decisions. 2, 5
All patients should be offered screening regardless of age or baseline risk, and NIPT represents the most sensitive and specific screening option for common aneuploidies. 2
Twin Pregnancies
- The Harmony test is validated for twin pregnancies, though detection rates are slightly lower than in singletons (95% for trisomy 21 in twins vs. 99% in singletons), and this performance is maintained when testing occurs in the 10-14 week window. 3
Clinical Bottom Line
There is no upper gestational age limit for performing the Harmony prenatal test after 13 weeks. The test can be performed at any point in the second or third trimester if clinically indicated. However, testing between 13-14 weeks may represent an optimal window, balancing early reassurance with reduced spontaneous loss rates and immediate access to amniocentesis for confirmation if needed. 5