First-trimester prenatal screening: PAPP-A, β-hCG — normal values and interpretation

Q: High screening risk — is the baby sick?

No. Screening is probability, not diagnosis: most pregnancies with “high risk” turn out healthy after NIPT or invasive testing. The next step is a geneticist consult.

Q: What is MoM?

Your result divided by the median for that gestational age. 1.0 MoM is exactly the middle; roughly 0.5–2.0 MoM is normal for both markers.

Q: Can I skip screening and take NIPT directly?

NIPT is more accurate for trisomies 21/18/13, but it is paid and does not replace the ultrasound. The approach is chosen with the obstetrician-gynecologist.

In shortFirst-trimester screening is the “double test”: PAPP-A and free β-hCG blood at 11–13+6 weeks plus ultrasound (including nuchal translucency). The result is not a diagnosis but a risk calculation in MoM. Normal for each marker is roughly 0.5–2.0 MoM; high risk calls for a geneticist consult.

What this marker is

Prenatal screening estimates the probability of chromosomal conditions (Down syndrome — trisomy 21, Edwards — 18, Patau — 13). Blood markers are measured in MoM — your result relative to the median for that gestational age.

It is important to understand: screening does not diagnose, it sorts risk. “High risk” only calls for noninvasive prenatal testing (NIPT) or invasive diagnostics as decided with a geneticist. Accuracy depends heavily on the correct gestational age and weight.

Reference ranges

Group	Reference range
Timing	strictly 11 weeks 0 days – 13 weeks 6 days
PAPP-A	normal about 0.5–2.0 MoM
Free β-hCG	normal about 0.5–2.0 MoM
Nuchal translucency (ultrasound)	usually < 2.5–3.0 mm — depends on the week
Individual risk	calculated with age, weight and gestational age

MoM depends on gestational age to the day: even 3–4 days of error skews the calculation. Weight, smoking and IVF are also entered into the program. Screening does not make a diagnosis. Ranges differ between laboratories.

Check your value

Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.

An approximate comparison with a typical range, not a diagnosis. Ranges differ between laboratories — use the one on your report; a doctor interprets the result.

When it is high or appears: possible causes

Risk above the cut-offThe program reports elevated risk — the next step is a geneticist consult and NIPT, not conclusions.

Low PAPP-AMay accompany not only anomalies but also preeclampsia risk — slightly closer observation.

Wrong gestational age or weightThe most common cause of a “bad” screening — dates are rechecked by ultrasound.

What can skew the result

These factors can shift the result without any disease — keep them in mind before a retest:

Inaccurate gestational ageWeight missing or wrongSmokingIVF and twins — separate corrections

How to prepare

Blood is taken the same day as the ultrasound, or within a few days — the program uses both. Timing is critical: 11 weeks 0 days to 13 weeks 6 days. Details: Preparation: venous blood.

When a retest makes sense

First-trimester screening is done once; the second stage is a second-trimester screening (16–20 weeks) as prescribed. With high risk there is no “retest” — there is NIPT or a geneticist consult.

Who usually reviews this result

An out-of-range result is usually reviewed by: Obstetrician-gynecologist, geneticist. Bring your report and any previous results to the visit.

Names used on lab reports

Look for one of these names on your report:
First-trimester screeningDouble testPAPP-Aβ-hCG

Several markers on your report?

The app reads your whole report — this marker together with its neighbors, not one by one.

Get your results explained See an example

Frequently asked questions

High screening risk — is the baby sick?