Stillbirth Risk Calculator - Pre-Pregnancy Scenario Index

A stillbirth risk calculator builds a scenario-adjusted risk index by combining the published US baseline fetal mortality rate at 20 or more weeks with twelve published pre-pregnancy odds ratios. The output is a relative index, not a calibrated personal probability, because the published odds ratios come from a case-control study, not from a validated pregnancy prediction model. The result is meant to support a conversation with a clinician, not to replace one.

• • Preconception Counseling: Bring a scenario-adjusted stillbirth risk index into a preconception visit, especially when age, BMI, or a comorbidity is part of the pregnancy plan.
• • Early Pregnancy Planning: Get a relative index for the first prenatal visit, so the conversation with the obstetrician starts with a shared number and a shared set of modifiable factors.
• • Comparing Risk Factors: See how much each published factor moves the relative index, so the focus on the most actionable factor is grounded in the published odds ratios.

The twelve inputs cover the four groups that move published stillbirth risk the most: demographic (age, ethnicity), anthropometric (height, weight, computed BMI), obstetric history (parity, ART use), and clinical plus lifestyle (diabetes, hypertension, lupus, APS, smoking, alcohol).

Once the scenario-adjusted index is on the page, the pregnancy calculator is a natural next step for dating the pregnancy and lining up the prenatal care schedule around the same set of risk factors.

The calculator reports one main number, a scenario-adjusted stillbirth risk index, plus a 1-in-X equivalent, a risk index against a healthy 28-year-old first-pregnancy reference, and the computed pre-pregnancy BMI. The index multiplies the US baseline fetal mortality rate by the published odds ratio for each of the twelve pre-pregnancy risk factors, a multiplicative combination of published ratios, not a calibrated prediction model.

• baselineRate: 0.00605, the US fetal mortality rate at 20+ weeks from Hoyert and Gregory 2016 NVSR.
• ageOR: 1.2 (<20), 1.1 (20-24), 1.0 reference (25-29), 1.3 (30-34), 1.8 (35-39), 2.8 (40-44), 5.5 (45+).
• ethnicityOR, bmiOR, parityOR, artOR: Ethnicity: 1.0 (white ref), 2.3 (Black), 1.1 (Hispanic), 1.4 (Asian), 1.2 (other). BMI: 1.3 (<18.5), 1.0 (18.5-24.9 ref), 1.2 (25-29.9), 1.6 (30-34.9), 2.5 (35+). Parity: 1.0 ref, 0.8 (1 prior), 0.9 (2 prior), 1.1 (3+). ART: 1.7 if yes.
• diabetesOR, hypertensionOR, lupusOR, apsOR, smokingOR, alcoholOR: Diabetes 3.5 (type 1) or 3.0 (type 2). Hypertension 1.7. Lupus 3.5. APS 2.5. Smoking 1.4 (light) or 1.9 (heavy). Alcohol 1.1 (occasional) or 1.4 (regular).

Each published odds ratio is applied as a separate multiplier, and the underlying case-control study reports each odds ratio as adjusted for the other factors, so the product is a first-order approximation rather than a claim that the underlying effects do not overlap.

According to CDC NVSR Fetal Death Report 2014 (Hoyert and Gregory 2016), the US fetal mortality rate at 20 weeks gestation or more was about 6.05 per 1,000 pregnancies in 2014, the baseline the index scales up from. According to Reddy UM et al. (Obstetrics & Gynecology 2010), the most important pre-pregnancy risk factors are non-Hispanic Black ethnicity, advanced maternal age, obesity, nulliparity, prior fetal loss, pre-existing diabetes, chronic hypertension, lupus, anti-phospholipid syndrome, and cigarette smoking, with adjusted odds ratios from 1.3 to 5.5 used to build this index.

The age and BMI odds ratios do most of the heavy lifting in this index, and the BMI in pregnancy calculator works the same BMI forward into a recommended pregnancy weight-gain range.

Four ideas are enough to understand the index and its limits.

The index starts from the published population baseline and then asks where this specific combination of pre-pregnancy factors would sit on the relative scale, given the published odds ratios. It is a useful planning index, not an individually calibrated prediction.

A stillbirth index is only as useful as the gestational age it lines up with, and the pregnancy due date calculator turns the same last menstrual period into an estimated due date that anchors the prenatal care timeline.

Refresh the inputs each time a risk factor changes, and use the relative index alongside a clinician's advice.

1. 1 Enter Age, Height, and Pre-Pregnancy Weight: Type maternal age, height in centimetres, and the pre-pregnancy weight in kilograms (not the current pregnancy weight). These inputs drive the age odds ratio and the computed BMI band.
2. 2 Pick Ethnicity and Previous Pregnancies: Choose the self-reported maternal ethnicity, then the count of previous pregnancies that reached 20 or more weeks.
3. 3 Indicate ART and Pre-Pregnancy Diabetes: Select whether the pregnancy was conceived with IVF or ICSI, and whether the mother had pre-pregnancy type 1 or type 2 diabetes.
4. 4 Indicate Hypertension, Lupus, and APS: Pick chronic hypertension, known SLE, and known anti-phospholipid syndrome.
5. 5 Pick Smoking and Alcohol Use: Select the cigarette dose (none, 1-9, 10+) and the alcohol dose (none, occasional, regular).
6. 6 Read the Three Outputs as a Relative Index: The scenario-adjusted percentage is the relative index, not a personal probability. The 1-in-X equivalent makes the same index familiar. The risk index compares the chosen combination to the healthy 28-year-old first-pregnancy reference.

A 42-year-old Asian, BMI 27, first pregnancy, IVF conceived, light smoker gives 0.00605 x 2.8 x 1.4 x 1.2 x 1.0 x 1.7 x 1.4 = 0.068, or about 6.77% on the relative index, roughly 1 in 15 and 11x the healthy reference.

The pre-pregnancy BMI is the single largest modifiable multiplier, and the pregnancy weight gain calculator translates that BMI into the Institute of Medicine weekly weight-gain target.

A scenario-adjusted stillbirth risk index is most useful when it changes a conversation in front of you.

• • Translates a Population Rate Into a Relative Index: The calculator turns the published US baseline fetal mortality rate into a relative index built from the chosen combination of factors.
• • Separates the Effect of Each Factor: Each input changes one published odds ratio, so the calculator shows how much of the relative index is age, BMI, ethnicity, parity, ART, comorbidity, or lifestyle.
• • Highlights Modifiable Versus Non-Modifiable Factors: BMI, smoking, and alcohol use are modifiable; age, ethnicity, ART, parity, and chronic conditions are not.
• • Source-Backed Numbers: Each odds ratio traces to a specific published case-control study, useful in a shared decision-making conversation about preconception optimization.

A 38-year-old with type 2 diabetes, chronic hypertension, and a pre-pregnancy BMI of 33 lands at about 16% on the relative index; the same combination with a BMI of 22 lands at about 1.4%.

Lupus, anti-phospholipid syndrome, and chronic hypertension all raise the relative index on this calculator, and the same set of factors also drives the venous thromboembolism risk that the VTE risk in pregnancy calculator models.

The same inputs can move the relative index by a factor of 100 or more.

• • The index covers pre-pregnancy risk factors only. It does not capture current-pregnancy complications such as pre-eclampsia, fetal growth restriction, or placental abruption, which are managed clinically.
• • The ethnicity odds ratio reflects a population average. Individual risk within an ethnic group varies widely, and the index should not be used to predict any one woman's outcome.
• • The index is a planning estimate built from a case-control study, not a calibrated clinical prediction tool validated in a separate pregnancy cohort.

The relative index should not be used to make a clinical decision on its own, to defer a clinician's advice, or to predict the outcome of a specific pregnancy.

According to ACOG Obstetric Care Consensus No. 10, pre-pregnancy risk factors such as diabetes, hypertension, lupus, and anti-phospholipid syndrome are routinely identified in prenatal care and addressed with preconception counseling, medication review, and closer fetal surveillance, the same factors this relative index surfaces.

Advanced maternal age is the single largest non-modifiable multiplier on this page, and the fertility by age calculator models the related age curve for natural conception and IVF success.