Stillbirth Risk Calculator
Free Stillbirth risk Calculator with medically-sourced formulas. Enter your measurements for personalized, accurate health insights.
Calculator
Adjust values & calculateIdentified Risk Factors
Recommended Monitoring
Formula
Where the baseline stillbirth rate varies by gestational age (approximately 1.5-8.0 per 1,000 from 20-43 weeks), and each identified risk factor contributes a multiplicative adjustment based on published relative risk data from large epidemiological studies. The cumulative risk is the product of all applicable multipliers applied to the gestational age-specific baseline rate.
Last reviewed: January 2026
Worked Examples
Example 1: Low-Risk 28-Year-Old at Term
Example 2: High-Risk 42-Year-Old with Multiple Risk Factors
Background & Theory
The Stillbirth Risk Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the Stillbirth Risk Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Frequently Asked Questions
Formula
Adjusted Risk = Baseline Rate x Product of Risk Factor Multipliers
Where the baseline stillbirth rate varies by gestational age (approximately 1.5-8.0 per 1,000 from 20-43 weeks), and each identified risk factor contributes a multiplicative adjustment based on published relative risk data from large epidemiological studies. The cumulative risk is the product of all applicable multipliers applied to the gestational age-specific baseline rate.
Worked Examples
Example 1: Low-Risk 28-Year-Old at Term
Problem: A 28-year-old woman at 39 weeks gestation, BMI 23, first pregnancy, no medical conditions, non-smoker. Calculate her stillbirth risk.
Solution: Baseline rate at 39 weeks: 3.0 per 1,000\nMaternal age <35: no adjustment (1.0x)\nBMI 23 (normal): no adjustment (1.0x)\nNo previous stillbirth: no adjustment (1.0x)\nNon-smoker: no adjustment (1.0x)\nNo diabetes or hypertension: no adjustment (1.0x)\nNulliparity: 1.2x multiplier\nAdjusted rate = 3.0 x 1.2 = 3.6 per 1,000\nRisk: approximately 1 in 278
Result: Risk: 3.6 per 1,000 (1 in 278) - Average Risk with standard monitoring recommended
Example 2: High-Risk 42-Year-Old with Multiple Risk Factors
Problem: A 42-year-old woman at 40 weeks, BMI 35, previous stillbirth, with gestational diabetes. Calculate cumulative risk.
Solution: Baseline rate at 40 weeks: 3.0 per 1,000\nAge 40+: 2.0x multiplier\nBMI 35 (obese): 1.8x multiplier\nPrevious stillbirth: 2.5x multiplier\nDiabetes: 2.0x multiplier\nCumulative multiplier: 2.0 x 1.8 x 2.5 x 2.0 = 18.0x\nAdjusted rate = 3.0 x 18.0 = 54.0 per 1,000\nRisk: approximately 1 in 19
Result: Risk: 54.0 per 1,000 (1 in 19) - High Risk. Enhanced surveillance and earlier delivery recommended
Frequently Asked Questions
What is stillbirth and how common is it in developed countries?
Stillbirth is defined as the death of a fetus at or after 20 weeks of gestation (in the United States) or 28 weeks (by WHO international comparison standards). In the United States, stillbirth affects approximately 1 in 160 pregnancies (about 24,000 per year), making it roughly 10 times more common than sudden infant death syndrome (SIDS). The rate varies significantly by gestational age, with the highest rates occurring before 28 weeks and after 41 weeks. Despite advances in prenatal care, the stillbirth rate has declined only modestly over the past two decades compared to dramatic reductions in infant mortality. About half of all stillbirths occur before 28 weeks, while the remainder occur in the third trimester.
What are the most significant risk factors for stillbirth?
The most significant modifiable and non-modifiable risk factors include advanced maternal age (over 35, with risk doubling over 40), obesity (BMI over 30 carries 1.5-2.5 times increased risk), smoking during pregnancy (approximately 1.5 times increased risk), and pre-existing medical conditions such as diabetes and hypertension (each doubling the risk). Previous stillbirth is one of the strongest risk factors, increasing risk 2-10 times depending on the cause of the prior loss. Racial disparities exist, with Black women in the United States experiencing nearly double the stillbirth rate compared to white women. Other factors include fetal growth restriction, placental abnormalities, multiple pregnancies, substance abuse, and certain infections. Many stillbirths have multiple contributing factors.
How does gestational age affect the risk of stillbirth?
The relationship between gestational age and stillbirth risk follows a U-shaped pattern. Early pregnancy losses (20-27 weeks) account for about 50% of all stillbirths and are often related to fetal anomalies, infections, or placental problems. Risk decreases during the early third trimester (28-36 weeks) but begins to rise again after 39 weeks. After 41 weeks, the prospective stillbirth risk increases significantly, which is a primary reason providers recommend induction of labor by 41-42 weeks. At 39 weeks the risk is approximately 1 in 3,000 per week of continuing pregnancy, but by 42 weeks it rises to approximately 1 in 500-1,000 per week. This increasing post-term risk reflects placental aging and the growing metabolic demands of a larger fetus.
Can fetal movement monitoring help prevent stillbirth?
Fetal movement monitoring (kick counting) is one of the few screening tools available to all pregnant women and may help identify fetuses at risk. The general recommendation is to begin daily kick counts around 28 weeks, counting during a time when the baby is typically active. A common method is to count 10 movements within a 2-hour period. Decreased fetal movement can indicate fetal compromise and has been associated with stillbirth, growth restriction, and other adverse outcomes. However, the evidence that formal kick counting programs reduce stillbirth rates is mixed, with some studies showing benefit and others showing no significant reduction. The key intervention is maternal awareness and prompt medical evaluation when decreased movement is noticed, as this can lead to timely delivery when fetal compromise is detected.
How does maternal obesity specifically increase the risk of stillbirth?
Obesity increases stillbirth risk through multiple mechanisms that affect both placental function and fetal development. Obese women have higher rates of gestational diabetes, preeclampsia, and chronic hypertension, all of which independently increase stillbirth risk. Excess adipose tissue produces inflammatory cytokines that can impair placental development and blood flow. Obese women are more likely to experience obstructive sleep apnea, which causes intermittent hypoxia that may affect fetal oxygenation. The increased metabolic demands of a larger maternal body may compromise placental reserve. Additionally, fetal growth abnormalities (both growth restriction and macrosomia) are more common in obese women. Studies show that the risk increases progressively with BMI: a BMI of 25-29 carries about 1.2 times the risk, BMI 30-39 carries 1.5-2 times, and BMI over 40 carries approximately 2.5 times the risk.
What investigations are performed after a stillbirth to determine the cause?
A comprehensive stillbirth evaluation aims to identify the cause to guide management of future pregnancies and provide families with answers. The evaluation typically includes a complete fetal autopsy (which identifies the cause in 40-60% of cases), placental pathology examination, karyotype or chromosomal microarray analysis of the fetus, maternal blood tests (including coagulation studies for thrombophilia, Kleihauer-Betke test for fetal-maternal hemorrhage, glucose and thyroid screening, infection screening for CMV, parvovirus, syphilis, and toxoplasmosis), and review of medical records for contributing factors. Despite thorough evaluation, the cause remains unexplained in approximately 25-60% of cases depending on the protocols used. Unexplained stillbirth is particularly distressing for families and complicates counseling for future pregnancy risks.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy