Stillbirth Risk Calculator
Free Stillbirth risk Calculator with medically-sourced formulas. Enter your measurements for personalized, accurate health insights.
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.