Early Maternal Screening Guidelines

Screening Options

The American College of Radiology recommends that both Panorama (cell-free fetal DNA) and nuchal translucency (NT) with first trimester combined screening are acceptable options, but no single screening test is superior to another in all test characteristics, so the choice depends on timing, cost considerations, and what additional information is wanted beyond aneuploidy screening 1, 2
First trimester combined screening (NT + serum markers) detects approximately 90% of affected pregnancies with a 5% false-positive rate 1, 2, 3

The patient will need two bloodwork requisitions for PAPP-A and free beta-hCG (or intact hCG) to be drawn during the same 11-14 week timeframe 1, 4
NT must be performed between 11+0 to 14+0 weeks of gestation, as the measurement loses predictive value outside this narrow window 5, 6
Provides early reassurance and timely detection with the option for earlier and safer pregnancy termination if abnormalities are found 1, 2
Identifies structural abnormalities that cell-free DNA cannot detect, and detects genetic syndromes like Noonan syndrome and 22q11.2 deletion syndrome that Panorama will miss 5
Particularly useful for twin gestations where each fetus can be assessed individually 7, 8

Has a higher detection rate for trisomy 21, but only screens for trisomies 21, 18, 13, and sex chromosome aneuploidies 5
Does not require the strict 11-14 week timing that NT does 6
Costs $400, and will miss structural heart defects, skeletal dysplasias, other genetic syndromes, and chromosomal abnormalities beyond the common trisomies 5, 4

Even with negative Panorama results, a second trimester anatomic survey at 18-22 weeks is still required 5
NT screening should never replace the standard second trimester anatomic fetal survey 1, 2
If NT is increased (≥3 mm), immediate genetic counseling and invasive diagnostic testing should be offered, and about one-third of fetuses with NT ≥3 mm will have chromosomal abnormalities 5, 6
Fetal echocardiography at 18-22 weeks is indicated even if karyotype is normal, as cardiac defects remain elevated risk 5

The American College of Radiology notes that NT measures a physical finding that correlates with aneuploidy risk, detecting approximately 70% of trisomy 21 cases when used alone, while NIPT analyzes cell-free fetal DNA in maternal blood with a higher detection rate for trisomy 21, 18, and 13 9
The American College of Radiology states that these tests measure fundamentally different markers, so normal results on one test do not guarantee normal results on the other 9, 10

A fetus can have a chromosomal abnormality detected by NIPT without having increased nuchal fluid accumulation, as noted by the American College of Radiology 9

A normal NT measurement at 12 weeks significantly reduces but does not eliminate the risk of chromosomal abnormalities, with NT alone detecting only approximately 70% of trisomy 21 cases, meaning 30% of Down syndrome fetuses will have normal NT measurements, according to the American College of Radiology 11
A normal NT measurement at 12 weeks indicates that only about 50% of major fetal anomalies can be detected prior to 14 weeks, with a false-positive rate of 3-4% at this early gestational age, as stated by the American College of Radiology 11
Less than 25% of major heart defects are detected using NT screening at the 99th percentile in euploid fetuses, confirming that most congenital heart disease cases have normal NT thickness, as reported by the American College of Radiology 11
A normal NT at 12 weeks does not screen for or exclude most cardiac defects, due to the strong association between increased NT and cardiac anomalies, as noted by the American College of Radiology 11

In dichorionic twins, calculate fetus-specific risks using each twin's individual NT measurement, and in monochorionic twins, use the average NT thickness of both fetuses for pregnancy-specific risk calculation, as recommended by the American College of Radiology 12
Standard singleton thresholds apply to twins, as NT distribution does not differ significantly between singletons and twins, according to the American College of Radiology 12

Never use NT screening to replace the standard second trimester anatomic fetal survey, regardless of how reassuring the first trimester results appear, as advised by the American College of Radiology 11
Do not perform NT solely for aneuploidy screening in patients with negative cell-free fetal DNA, as this approach is not recommended by the American College of Radiology 12