Stillbirth Risk Calculator

Introduction

This stillbirth risk calculator estimates the chance of stillbirth in a current pregnancy based on maternal, medical, and pregnancy factors. It’s built for expectant parents and clinicians who want a quick, numbers-based look at risk without digging through published cohort studies. The tool uses baseline risk figures by race and ethnicity, then adjusts for factors like age, BMI, diabetes, chronic hypertension, smoking, plurality, and obstetric history. A 38-year-old woman with pre-gestational diabetes and a BMI of 34 will get a different estimate than a 25-year-old with none of those factors. That’s the point. The output is a risk estimate per 1,000 births, a relative risk multiplier, and a plain-language risk category. It’s not a diagnosis. It’s a starting point for a more informed conversation with a provider.

How to Use the Stillbirth Risk Calculator

1. Pick a preset from the dropdown if you want a starting point. Options include average-risk pregnancy, advanced maternal age, obesity with gestational diabetes, previous stillbirth, and a high-risk profile.

2. Enter your age in years. The tool accepts ages 15 through 55.

3. Choose your race or ethnicity. This sets the baseline risk because stillbirth rates differ by population group.

4. Set gestational age in weeks. Anything from 20 to 43 weeks works.

5. Select plurality. Singleton, twins, or triplets and higher.

6. Choose your parity: no previous births, one to two, or three or more.

7. Enter pre-pregnancy BMI. The field accepts decimals, so 23.4 is fine.

8. Answer the medical history questions: chronic hypertension, diabetes type, preeclampsia, smoking status, previous stillbirth, prior preterm birth, IUGR, substance use, and ART use.

9. Tap Calculate. The result updates automatically as you change inputs, but the button forces a recalculation if you want one.

How the Stillbirth Risk Calculator Formula Works

The tool uses a multiplicative risk model. It starts with a baseline stillbirth rate per 1,000 births for your racial or ethnic group, applies a gestational age modifier, then multiplies by a relative risk factor built from your individual inputs.

Formula: Risk per 1,000 = Baseline × GA modifier × Relative Risk

The baseline values range from 4.4 per 1,000 for Asian-American pregnancies to 10.5 per 1,000 for African-American pregnancies. The gestational age modifier adjusts risk based on how much pregnancy remains. Earlier gestations carry a higher modifier because more time remains at risk. At 28 weeks the modifier is 1.30; at 39 weeks it drops to 0.90; at 42 weeks and beyond it’s 0.60.

The relative risk multiplier is where the individual factors come in. Each factor has a published odds ratio or relative risk. The tool multiplies them together in log space, which is a standard epidemiological approach. Age 40 or older adds a 1.9× multiplier. Pre-gestational diabetes adds 2.5×. Previous stillbirth adds 3.0×. IUGR adds 2.8×. Twins add 2.5×. These multiply, so a pregnancy with three moderate risk factors can end up with a substantial combined relative risk.

The final risk per 1,000 is clamped between 0.3 and 300. That prevents extreme outliers from producing nonsensical results. The percentage shown is simply the per-1,000 figure divided by 10.

Worked Example

Let’s walk through a 36-year-old woman, white, 37 weeks pregnant with a singleton. She’s had one previous birth. Her BMI is 31. She has gestational diabetes and smoked during the first trimester but quit. No chronic hypertension, no preeclampsia, no previous stillbirth, no IUGR, no substance use, no ART.

Start with baseline: 4.8 per 1,000 for white race.

Gestational age modifier at 37 weeks: 1.00.

Now the relative risk multipliers. Age 36 falls in the 35–39 bracket, so that’s 1.5×. BMI 31 falls in the 30–34.9 bracket, so 1.4×. Gestational diabetes adds 1.3×. Quit smoking adds 1.2×. Parity of 1–2 doesn’t add anything; nulliparous would add 1.2× but she’s not nulliparous.

Multiply those together: 1.5 × 1.4 × 1.3 × 1.2 = 3.276.

Baseline × GA modifier × RR = 4.8 × 1.00 × 3.276 = 15.72 per 1,000.

That’s about 1.57% risk. The tool would categorize this as moderate risk, because it falls in the 10–19.9 per 1,000 band. The relative risk display would show 3.28×. The verdict banner would suggest discussing increased surveillance with a provider — growth scans, fetal movement awareness, that sort of thing.