Enter screening details
The page uses a single-column flow, while the form fields shift to three columns on large screens, two on medium screens, and one on mobile.
Example data table
| Maternal age | GA | CRL | NT | PAPP-A | free β-hCG | Nasal bone | Example outcome |
|---|---|---|---|---|---|---|---|
| 32 years | 12w 4d | 62 mm | 1.7 mm | 1.10 MoM | 1.30 MoM | Present | Lower flag pattern |
| 39 years | 12w 1d | 58 mm | 3.2 mm | 0.35 MoM | 2.60 MoM | Absent | Prompt follow-up priority |
Formula used
Important: this page does not recreate a validated hospital screening algorithm. It produces an educational review score for discussion support.
- Screening window check: Eligible when gestational age is 11w 2d to 14w 1d and CRL is 45 to 84 mm.
- Age background chance: An interpolated age reference table estimates a background trisomy 21 chance as
1 in N. - NT points: 0 points below 2.5 mm, 5 points from 2.5 to 2.99 mm, 18 points from 3.0 to 3.49 mm, and 30 points at 3.5 mm or above.
- PAPP-A points: 0 points at 1.0 MoM or above, 8 points from 0.5 to 0.99, 14 points from 0.4 to 0.49, 22 points from 0.2 to 0.39, and 25 points below 0.2.
- free β-hCG points: 0 points from 0.5 to 2.0 MoM, 8 points from 0.2 to 0.49 or above 2.0 to 5.0, and 15 points below 0.2 or above 5.0.
- Nasal bone and history points: Absent nasal bone adds 5 points, not assessed adds 2 points, and previous affected pregnancy adds 8 points.
- Educational review score:
(raw points ÷ 108) × 100.
How to use this calculator
- Enter maternal age, pregnancy type, gestational age, and CRL.
- Add first-trimester NT, PAPP-A MoM, and free β-hCG MoM values.
- Select nasal bone status and any relevant pregnancy history items.
- Press Calculate screening summary to show results above the form.
- Review the marker table, top drivers, score, and follow-up note.
- Use CSV or PDF export to save a discussion copy for appointments.
- Do not use this page to self-diagnose or delay care.
Frequently asked questions
1) What does this calculator actually estimate?
It builds an educational screening snapshot from age, NT, PAPP-A, free β-hCG, and selected ultrasound context. It does not provide a clinical diagnosis or a laboratory-issued combined-risk result.
2) Why is the result called an educational review score?
Validated prenatal screening software uses calibrated statistical models and population adjustments. This page instead uses transparent rule-based scoring so users can organize information before discussing official results with a clinician.
3) When is first-trimester combined screening usually performed?
It is typically reviewed in the late first trimester, and this page checks a common window of 11 weeks 2 days to 14 weeks 1 day alongside a CRL range check.
4) What is MoM?
MoM means multiples of the median. A value of 1.0 sits at the median for the relevant reference population, while lower or higher values show how far a marker shifts from that median.
5) Does a higher score mean my baby definitely has a condition?
No. A higher score only means more review flags are present in this educational model. Official screening and diagnostic pathways may include repeat review, NIPT, chorionic villus sampling, or amniocentesis.
6) Why are twin pregnancies flagged as limited?
Twin pregnancies usually need specialist interpretation because marker behavior and formal risk models differ from singleton pregnancies. This page keeps the output visible but warns that a twin-specific clinical pathway is needed.
7) What should I do if PAPP-A is low?
Use the result to prepare questions for your maternity clinician. Low PAPP-A can prompt closer follow-up, but it does not by itself confirm that a fetal chromosome condition is present.
8) Why can I export CSV and PDF files?
The exports help you keep a structured summary of inputs, marker flags, and follow-up notes. They are useful for record keeping, team review, and appointment preparation.
Clinical caution
This calculator is for education and appointment preparation only. Seek urgent care now for bleeding, severe pain, fainting, or other concerning symptoms. Never delay clinical advice because of a web calculator.