Estimate live birth without trisomy 21, 18 or 13 using pregnancy timing, screening results and optional pregnancy factors.
For donor eggs, use the egg provider’s age at retrieval.
We will convert your EDD to gestational age for today.
This only changes the three named trisomy states. A normal result does not exclude every genetic or health condition. An inconclusive result does not replace the current chance estimate.
General inputs (optional)
If blank, BMI is calculated from height and weight when available. Otherwise, BMI 26 is used.
Early pregnancy factors (miscarriage) (optional)
At week 11 or later, selecting no heartbeat stops the estimate and shows a safety message.
Optional. A slow heart rate can increase the early-pregnancy risk estimate.
Later pregnancy factors (stillbirth) (optional)
If you do not want ethnicity included, leave it unselected.
Default is about 1 in 160. You can change this to match your region.
Advanced stillbirth inputs (optional)
Neonatal survival assumptions (optional)
Change chromosome risk chances
These defaults update from the selected age and gestational age until you edit a number. Edit any individual number to use your own starting chance for that trisomy.
Sources and how they were used
- Snijders maternal-age and gestational-age trisomy tables: The published tables supply the starting chances for T21, T18 and T13 at 10, 12, 14, 16, 20 and 40 weeks. The calculator interpolates probabilities between published cells and uses the change to 40 weeks for the condition-specific live-birth component.
- SMFM Consult Series #74: Table 2 supplies the default sensitivity and specificity used to update the three chromosome chances after a low-risk or high-risk NIPT result.
- ACOG screening guidance: Used to distinguish screening from diagnosis and to prevent a nonreportable result from being treated as low risk.
- Bhattacharya et al. 2010, Regan et al. 2006, and Doubilet and Benson 1995: Describe associations involving previous pregnancies and fetal heart rate. The resulting estimate is educational rather than an individualized clinical prediction.
- Ammon Avalos et al. 2012 and Nybo Andersen et al. 2000: Describe how miscarriage risk varies with gestational age and maternal age. Individual risk may differ from the estimate shown.
- CDC fetal-death data and ACOG stillbirth guidance: Provide population context for the stillbirth estimate and listed risk factors. The combined result is not a validated individualized stillbirth prediction.
- CDC infant-mortality reporting: Used only as context for the optional birth-to-discharge and 28-day outputs. The percentages are user-editable assumptions and are not individualized neonatal predictions.
- ACOG amniocentesis guidance and NHS guidance for amniocentesis and CVS: Explain how CVS and amniocentesis provide diagnostic chromosome results. Procedure-related pregnancy-loss risk is not included in the result on this page.
Method reviewed: 12 July 2026. This calculator is educational. It estimates live birth without three named trisomies, not whether every chromosome or gene is normal.