Stillbirth Risk Calculator
This calculator estimates the probability of stillbirth (fetal loss at 20 weeks or later) using a multiplier model built from peer-reviewed epidemiological studies. Enter maternal characteristics and medical history to see a personalised risk estimate, a breakdown of contributing factors, and guidance on what the numbers mean. Results are for educational purposes and do not replace clinical assessment by a healthcare provider.
What is stillbirth and how common is it?
Stillbirth is defined as fetal death at or after 20 weeks of gestation. In the United States, approximately 5.5 fetal deaths occur per 1,000 pregnancies (CDC 2023). This translates to roughly 1 in 181 pregnancies, making it more common than many people realise. Globally, an estimated 2 million stillbirths occur each year, the majority in low- and middle-income countries. Causes include placental dysfunction, fetal growth restriction, chromosomal abnormalities, umbilical cord accidents, infection, and maternal medical conditions. In roughly 25-30% of cases in high-income countries, no definitive cause is identified even after thorough investigation.
How this calculator works
The calculator uses a multiplicative adjusted-odds-ratio (OR) model. Each documented risk factor is associated with an OR derived from large epidemiological studies and meta-analyses, principally the Stillbirth Collaborative Research Network (SCRN) case-control study (Silver et al., JAMA 2007), Gardosi et al.'s population-based UK cohort (BMJ 2013), and maternal-age meta-analyses. The baseline probability (0.553%, CDC 2023) is converted to odds, then multiplied by each applicable OR, and converted back to probability. Because the model treats all risk factors as independent, the estimate may overstate combined risk when factors are correlated. The result is an educational estimate only, not a clinical diagnosis.
Risk factors you can modify
Several risk factors for stillbirth are modifiable. Stopping smoking before or during pregnancy reduces risk, with studies showing that quitting even after the first trimester provides benefit. Achieving a healthy pre-pregnancy BMI lowers risk associated with obesity. For women with diabetes, tight glycaemic control before and during pregnancy substantially reduces excess risk. Women with antiphospholipid syndrome can benefit from anticoagulation therapy (low-dose aspirin plus low-molecular-weight heparin) which has been shown to reduce fetal loss. Alcohol avoidance during pregnancy is universally recommended. Hypertension management, including low-dose aspirin from 12 weeks for high-risk women, is standard preventive care.
Risk factors that require enhanced monitoring
Some risk factors cannot be changed but can be managed with closer surveillance. Women with a previous stillbirth face approximately 6-fold elevated odds and typically receive enhanced antenatal care including regular growth scans, uterine artery Dopplers, and formalised fetal movement counting. Advanced maternal age (35+) warrants third-trimester monitoring including non-stress tests. Multiple medical conditions such as SLE, APS, type 1 or type 2 diabetes, and chronic hypertension should be co-managed by obstetric and specialist teams before and throughout pregnancy. Awareness of reduced fetal movement and prompt reporting to a healthcare provider is recommended for all pregnant women.
Key risk factors and their adjusted odds ratios
| Risk factor | Category | Approx. adjusted OR | Source |
|---|---|---|---|
| Maternal age | Under 20 | 1.2 | Registry data |
| Maternal age | 20-34 (reference) | 1.0 | - |
| Maternal age | 35-39 | 1.65 | CMAJ 2008 meta-analysis |
| Maternal age | 40+ | 2.29 | CMAJ 2008 meta-analysis |
| BMI | Normal 18.5-24.9 (reference) | 1.0 | - |
| BMI | Overweight 25-29.9 | 1.15 | CDC / Gardosi 2013 |
| BMI | Obese class I 30-34.9 | 1.4 | Gardosi et al., BMJ 2013 |
| BMI | Obese class II 35-39.9 | 1.6 | Gardosi et al., BMJ 2013 |
| BMI | Extreme obesity 40+ | 2.1 | Pooled estimate |
| Ethnicity | White non-Hispanic (reference) | 1.0 | - |
| Ethnicity | Black non-Hispanic | 2.12 | SCRN (Silver et al. 2007) |
| Parity | Nulliparous (no prior births) | 1.98 | SCRN (Silver et al. 2007) |
| Parity | 1-2 prior births (reference) | 1.0 | - |
| Parity | 3+ prior births | 1.6 | Gardosi et al., BMJ 2013 |
| Previous stillbirth | Yes | 5.91 | SCRN (Silver et al. 2007) |
| IVF / ART | Yes | 1.5 | Pooled meta-analysis |
| Diabetes | Type 1 | 3.9 | Gardosi / SCRN composite |
| Diabetes | Type 2 | 3.0 | Registry-based estimate |
| Diabetes | Gestational | 1.5 | Pooled estimate |
| Chronic hypertension | Yes | 2.5 | Literature midpoint |
| SLE / lupus | Yes | 2.4 | Systematic review |
| Antiphospholipid syndrome | Yes | 6.65 | Galli et al. meta-analysis |
| Smoking | Light (<10/day) | 1.55 | SCRN (Silver et al. 2007) |
| Smoking | Heavy (10+/day) | 2.5 | Gardosi et al., BMJ 2013 |
| Alcohol use | Yes | 1.4 | Registry-based estimate |
Odds ratios from major peer-reviewed studies used in this calculator. All are relative to a reference group with the lowest risk within that factor. Individual study details vary.
Frequently asked questions
Is this calculator accurate?
The calculator provides an educational estimate based on adjusted odds ratios from large, peer-reviewed epidemiological studies. It cannot account for all clinical variables, fetal factors, placental findings, or real-time pregnancy data. The model treats risk factors as independent, which can overestimate combined risk when factors are correlated. Use this tool to better understand relative risk and to inform conversations with your healthcare provider, not as a clinical diagnosis.
What is the difference between relative risk and absolute risk?
Absolute risk is the actual probability of the outcome (for example, 0.55% for the U.S. baseline). Relative risk is how many times greater your estimated risk is compared to the baseline. A relative risk of 3 means your estimated probability is three times the baseline, but if the baseline is 0.55%, three times that is 1.65%, still a low absolute probability. Both numbers matter for understanding your situation.
Does having multiple risk factors multiply the risks together?
In this model, yes. The calculator multiplies the odds ratios of all selected risk factors together. In reality, some risk factors are correlated (obesity often co-occurs with hypertension and diabetes), so the true combined risk may be somewhat lower than this model estimates. The calculator may therefore be conservative (overestimating combined risk) in some profiles.
Can I use this calculator if I have already had a stillbirth?
Yes. The previous stillbirth input is included because it carries the highest odds ratio in the model (approximately 5.9 times the baseline, from the SCRN study). If you have experienced a stillbirth, please seek care from a specialist in recurrent pregnancy loss or maternal-fetal medicine, who can offer tailored investigation and monitoring.
Does this calculator predict stillbirth in this pregnancy?
No. It estimates a statistical risk based on maternal characteristics. Many women with multiple risk factors have healthy pregnancies, and some stillbirths occur in women with no identifiable risk factors. This tool supports awareness and conversation, not prediction of individual outcomes.
How does ethnicity affect stillbirth risk?
Population-based studies consistently find that Black non-Hispanic women face approximately twice the stillbirth risk compared to White non-Hispanic women after adjusting for medical comorbidities. This disparity is partially explained by differences in rates of hypertension, diabetes, and access to care, but a substantial gap persists after adjusting for known factors, reflecting systemic inequities in maternal care. Advocacy for equitable care, bias-aware clinical practice, and inclusive research is an active area of maternal health policy.
What should I do if my estimated risk is high?
Share the result with your obstetrician or midwife. They can review your full clinical picture and recommend appropriate management - this may include additional ultrasound surveillance, uterine artery Doppler assessment, fetal movement counting protocols, low-dose aspirin if not already prescribed, or referral to a maternal-fetal medicine specialist. Do not rely on this calculator alone to guide clinical decisions.
Sources
- Silver RM et al. (SCRN). "Association Between Stillbirth and Risk Factors Known at Pregnancy Confirmation." JAMA 2011; 306(22):2469-79. PMC3807602
- Gardosi J et al. "Maternal and fetal risk factors for stillbirth: population based study." BMJ 2013;346:f108. PMC3554866
- CDC National Center for Health Statistics. "Fetal Mortality: United States, 2023." NVSR 74(8).
- Huang DY et al. "Maternal age and risk of stillbirth: a systematic review." CMAJ 2008;178(2):165-72. PMC2175002