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Stillbirth Risk Calculator

Stillbirth affects approximately 1 in 160 pregnancies in the USA. This calculator estimates individual risk by evaluating maternal age, BMI, medical conditions (diabetes, hypertension, lupus, antiphospholipid syndrome), obstetric history, assisted reproductive technology use, and modifiable factors like smoking and alcohol consumption. The assessment draws from CDC data and peer-reviewed research to provide personalised risk stratification.

Last updated:

Creators Łucja Zaborowska, MD, PhD
8,465 people find this calculator helpful

Stillbirth versus Miscarriage: Key Distinctions

Stillbirth and miscarriage both represent pregnancy loss, but they differ fundamentally in timing. A miscarriage occurs before 20 weeks of gestation, when foetal development is incomplete. Stillbirth, by contrast, is the loss of a baby at 20 weeks or later, including losses during labour and delivery.

Stillbirth is further classified by gestational age: early stillbirth (20–27 weeks), late stillbirth (28–36 weeks), and term stillbirth (37+ weeks). Understanding this distinction is important because the causes, investigations, and emotional responses differ significantly. Medical management and bereavement support also vary based on the type of loss.

How Stillbirth Risk Is Calculated

The calculator applies evidence-based risk multipliers to a baseline population risk. It combines odds ratios derived from large epidemiological studies with individual maternal and obstetric factors to produce an individualised estimate.

Stillbirth Risk = Baseline Risk × Age Factor × BMI Factor × Parity Factor
                                                           × Smoking Factor × Alcohol Factor
                                                           × Ethnicity Factor × Diabetes Factor × Hypertension Factor
                                                           × Lupus Factor × Antiphospholipid Syndrome Factor × ART Factor

BMI = Weight (kg) ÷ Height (m)²

  • Baseline Risk — The population-level stillbirth incidence, typically set to 1 in 455 for the general US population.
  • Age Factor — Stillbirth risk increases at maternal ages below 20 and above 35, with the highest risk at age 50+.
  • BMI Factor — Underweight (BMI < 18.5) and obese (BMI ≥ 30) individuals face elevated risk compared to the normal range.
  • Parity Factor — First pregnancies carry different baseline risk than multipara; previous preterm births or caesarean deliveries modify this factor.
  • Smoking Factor — Current smoking substantially increases stillbirth risk; the factor reflects dose-dependent effects.
  • Alcohol Factor — Regular or heavy alcohol consumption during pregnancy increases risk significantly.
  • Ethnicity Factor — Risk varies by racial and ethnic background due to complex interactions with access to care, genetics, and comorbidities.
  • Diabetes Factor — Both pre-existing and gestational diabetes substantially elevate stillbirth risk.
  • Hypertension Factor — Chronic hypertension or pregnancy-related hypertensive disorders increase risk.
  • Lupus Factor — Systemic lupus erythematosus (SLE) is an autoimmune condition associated with increased stillbirth risk.
  • Antiphospholipid Syndrome Factor — This thrombophilic condition increases placental blood clotting and stillbirth risk.
  • ART Factor — Assisted reproductive technologies such as IVF, ICSI, and fertility medications modify risk independently of maternal age.

Leading Causes and Risk Pathways

Stillbirth is multifactorial; no single pathway explains all cases. Common aetiologies include:

  • Placental insufficiency — the placenta fails to deliver adequate oxygen and nutrients, often linked to maternal hypertension, diabetes, or pre-eclampsia.
  • Cord accidents — umbilical cord knots, wrapping, or compression restrict foetal blood supply.
  • Foetal anomalies — structural or chromosomal abnormalities incompatible with life.
  • Intrauterine infections — viral, bacterial, or parasitic infections that cross the placental barrier.
  • Maternal chronic diseases — lupus and antiphospholipid syndrome cause recurrent thrombosis; uncontrolled diabetes damages maternal vasculature and foetal development.
  • Lifestyle factors — smoking and alcohol use both directly harm foetal development and reduce placental perfusion.

Many cases remain unexplained despite thorough postmortem investigation, underscoring the complexity of pregnancy loss.

Key Considerations and Risk Reduction Strategies

Lowering stillbirth risk requires proactive management of modifiable factors and close antenatal surveillance.

  1. Smoking and Alcohol Cessation — Both carry substantial, dose-dependent effects on stillbirth risk. Smoking reduces placental perfusion and increases foetal hypoxia. Alcohol is teratogenic and disrupts placental development. Cessation at any point during pregnancy improves outcomes; the earlier, the greater the benefit.
  2. Glycaemic and Blood Pressure Control — Women with diabetes must achieve strict glycaemic targets (HbA1c < 6.5% where safely possible) before conception and throughout pregnancy. Similarly, hypertension requires aggressive management to maintain blood pressure below 140/90 mmHg, reducing the risk of placental abruption and infarction.
  3. Pre-pregnancy BMI Optimisation — Obese women (BMI ≥ 30) face elevated risk from inflammation, insulin resistance, and placental dysfunction. A 5–10% weight loss before conception can substantially reduce risk. Underweight women (BMI < 18.5) should gain appropriate weight to support placental development.
  4. Antenatal Monitoring and Shared Care — Women with high-risk factors should receive increased antenatal surveillance, including more frequent growth scans, Doppler studies, and foetal movement monitoring. Multidisciplinary care involving maternal-foetal medicine specialists optimises outcomes and allows early intervention if problems emerge.

Frequently Asked Questions

How is stillbirth defined and distinguished from early pregnancy loss?

Stillbirth is defined as the loss of a pregnancy at 20 weeks of gestation or later, or a baby born with no signs of life after 350 g of weight. Earlier losses, termed miscarriage or spontaneous abortion, occur before 20 weeks. The 20-week boundary reflects a shift in UK and many international guidelines; some jurisdictions use 22 weeks. This distinction has clinical importance because investigations, counselling, and statutory registration differ. Stillbirth often requires a postmortem examination to identify the cause, whereas early miscarriage may not.

What is the actual frequency of stillbirth, and does it vary by region?

In the USA, approximately 1 in 160 pregnancies ends in stillbirth, translating to roughly 21,000 cases annually. Worldwide, the rate is substantially higher at approximately 1 in 72 pregnancies, reflecting differences in prenatal care access, maternal nutrition, infection rates, and healthcare infrastructure. Low- and middle-income countries bear the heaviest burden, with rates exceeding 1 in 50 in some sub-Saharan African regions. Even within high-income countries, significant disparities exist by race, ethnicity, and socioeconomic status.

Can stillbirth risk be completely prevented, or only reduced?

Stillbirth cannot be completely prevented, as some causes (foetal anomalies, unexpected cord accidents, certain infections) occur despite optimal care. However, evidence-based interventions substantially lower risk. Smoking cessation, tight glycaemic control, blood pressure management, weight optimisation, and enhanced antenatal monitoring all reduce individual risk by 20–40% or more. Regular antenatal care, including ultrasound assessment of foetal growth and amniotic fluid volume, allows early detection of problems amenable to intervention such as planned preterm delivery when intrauterine complications arise.

How do pre-existing medical conditions like lupus and diabetes affect stillbirth risk?

Both conditions significantly elevate risk through distinct mechanisms. Lupus (systemic lupus erythematosus, or SLE) and antiphospholipid syndrome cause placental inflammation and blood clots within the placenta, leading to infarction and foetal hypoxia. Diabetes increases stillbirth risk through hyperglycaemia-induced placental damage, foetal macrosomia (excessive growth), and cord compression. Women with these conditions require specialist care, intensive monitoring, and often prophylactic medications (anticoagulants, aspirin, immunosuppressants) to optimise outcomes. Pre-conception counselling and tight disease control before pregnancy conception are essential.

Does maternal age independently increase stillbirth risk?

Yes, stillbirth risk rises markedly with advancing maternal age. Women aged 35–39 face approximately 1.5–2 times the risk of women aged 20–29, whilst those aged 45+ face 3–4 times higher risk. This increased risk reflects age-related changes in egg quality (leading to chromosomal abnormalities), declining placental function, and higher rates of chronic diseases (hypertension, diabetes). Notably, very young mothers (under 20) also face elevated risk, particularly if coupled with poor prenatal care. Advanced paternal age contributes independently to some congenital anomalies, though maternal age remains the dominant factor for stillbirth.

How should ethnicity data be interpreted when assessing stillbirth risk?

Ethnicity is a proxy marker for biological, social, and structural factors affecting stillbirth risk, not a direct causal factor. Black mothers in the USA and UK face 2–3 times higher stillbirth rates than white mothers, driven by structural racism, systemic healthcare disparities, higher rates of hypertension and diabetes, and reduced access to timely specialist care. Indigenous and other minority populations show similar patterns. Using ethnicity in risk models requires careful interpretation to avoid reinforcing harmful stereotypes. The focus should be on addressing the underlying inequities—ensuring equitable access to prenatal care, managing chronic diseases aggressively, and fostering trust in healthcare systems—rather than attributing risk to ethnicity itself.

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