How we calculate miscarriage risk using peer-reviewed research
Pregnalyze's risk calculator is built on peer-reviewed studies published in leading medical journals. Our FREE calculator uses 5 foundational studies with data from over 50,000 pregnancies. Our PREMIUM calculator incorporates 65+ scientific references covering 40+ additional risk factors.
Our algorithm uses population-level data to estimate individual risk. It's important to understand that these are statistical estimates, not predictions. Every pregnancy is unique, and many factors we cannot measure also influence outcomes.
Scientific Transparency: All our risk modifiers are backed by published research from leading medical journals including BMJ, Lancet, NEJM, and Cochrane Reviews. See the tables below for complete FREE calculator references and PREMIUM factor citations.
Tong et al. (2008) - Obstetrics & Gynecology
“Miscarriage Risk for Asymptomatic Women After a Normal First-Trimester Prenatal Visit”
What we use: Establishes baseline miscarriage risk by week of pregnancy. Risk decreases significantly after 6-8 weeks when fetal heartbeat is detected.
Sample size: Study of asymptomatic women with confirmed intrauterine pregnancy
Magnus et al. (2019) - BMJ
“Role of maternal age and pregnancy history in risk of miscarriage: prospective register based study”
What we use: Clear demonstration of how maternal age and previous pregnancy outcomes affect current pregnancy risk. Foundation for our age-adjusted calculations.
Sample size: 421,127 pregnancies from Norwegian registries
Zhu et al. (2024) - JAMA Network Open
“Association of Prepregnancy Body Mass Index and Gestational Weight Gain With Pregnancy Outcomes”
What we use: Recent large-scale analysis showing correlation between BMI and pregnancy outcomes. Both underweight and obese categories show elevated risk.
Finding: BMI outside the normal range (18.5-24.9) is associated with increased miscarriage risk
BMJ Meta-analyses (2014) - BMJ
Smoking (Pineles et al.) and Caffeine (Greenwood et al.) systematic reviews and meta-analyses
What we use: Dose-response relationships for smoking and caffeine intake. These comprehensive meta-analyses synthesize multiple studies to establish population-wide risk estimates.
Sample size: Combined data from 20+ individual studies
Multiple sources (2006-2012) - BMJ, Lancet, NEJM
Studies on diabetes (Inkster et al.), thyroid antibodies (Negro et al.), and antiphospholipid syndrome (Rai et al.)
What we use: Risk modifiers for medical conditions that affect pregnancy outcomes, including both untreated risks and protective effects of treatment.
Finding: Many medical conditions increase risk, but proper management significantly reduces it
Step-by-step process:
Input: 32-year-old woman, 8 weeks pregnant, BMI 24, no previous miscarriages, 1 previous birth
Process:
Result: 8.8% risk (Low category)
Our FREE calculator uses these core validated factors with published coefficients from peer-reviewed journals:
| Risk Factor | Coefficient | 95% CI | Reference |
|---|---|---|---|
| Maternal age (variable by age) | Variable | — | Magnus et al., 2019 |
| Previous miscarriages | Variable | — | Magnus et al., 2019 |
| BMI (Body Mass Index) | Variable | — | Zhu et al., 2024 |
| Heartbeat detection | Variable | — | Tong et al., 2008 |
| TPO antibodies positive | OR 2.5 | 2.0–3.3 | Negro et al., 2011 |
| APS (untreated) | OR 10.0 | 5.3–19.4 | Rai et al., 2006 |
| APS (with treatment) | OR 0.5 | 0.27–0.78 | Ruffatti et al., 2010 |
| Diabetes Type 1 | OR 2.5 | 2.0–3.5 | BMJ Meta-analysis, 2012 |
| Diabetes Type 2 | OR 2.0 | 1.5–2.8 | BMJ Meta-analysis, 2012 |
| Smoking (light, 1-9/day) | RR 1.07 | 0.92–1.25 | BMJ Meta-analysis, 2014 |
| Smoking (moderate, 10-19/day) | RR 1.14 | 1.03–1.25 | BMJ Meta-analysis, 2014 |
| Smoking (heavy, ≥20/day) | RR 1.32 | 1.19–1.47 | BMJ Meta-analysis, 2014 |
| Paternal age ≥40 | RR 1.2 | 1.0–1.4 | Du et al., 2020 |
| Caffeine >300mg/day | RR 1.4 | 1.2–1.6 | Greenwood et al., 2010 |
| Alcohol ≥2 drinks/week | RR 1.2 | 1.1–1.3 | Sundermann et al., 2020 |
Note: OR = Odds Ratio, RR = Relative Risk, CI = Confidence Interval. All coefficients are adjusted for confounding factors as reported in the original studies.
Our PREMIUM calculator analyzes 40+ additional factors beyond the FREE version, all backed by peer-reviewed research. We use 65+ scientific references from leading medical journals.
We're committed to scientific rigor. All PREMIUM factors have published coefficients and confidence intervals. You can review the complete scientific backing at:
View Complete Scientific ReferencesReferences: Doubilet (NEJM 2013), Saraswat (BJOG 2010), Rubio (Fertil Steril 2017), and 10+ additional studies
References: Inkster (BMJ 2006), Maraka (Thyroid 2016), Robertson (Br J Haematol 2006), and 15+ additional studies
References: Cardozo (2021), Conner (Obstet Gynecol 2016), Pineles (Am J Epidemiol 2014)
References: Leitich (Am J Obstet Gynecol 2003), Nielsen (BMJ 2001), Haas (Cochrane 2013)
Unlike the FREE calculator which uses single point estimates, PREMIUM factors often show ranges (e.g., OR 1.5-2.0) because:
Our algorithm intelligently selects coefficients within these ranges based on your specific inputs and condition severity.
We believe in complete transparency about what our calculator can and cannot do:
Our calculator provides population-level statistics. A “10% risk” means that in a group of 100 similar women, about 10 would experience miscarriage. It does NOT mean you personally have a 10% chance.
We model each risk factor (age, BMI, history) as independent variables. In reality, these factors may interact in complex ways we cannot fully capture.
Many factors affect pregnancy outcomes that we don't measure: chromosomal abnormalities, uterine anatomy, immune factors, environmental exposures, stress, nutrition, and more.
Our algorithm is based on studies from 1998-2024, with most references from 2010-2020. While these remain current gold standards, medical understanding continues to evolve.
Many published coefficients have wide confidence intervals, reflecting uncertainty in the medical literature. We use conservative estimates and provide confidence ranges in our results.
This calculator should NEVER delay you from seeking medical care. Contact your healthcare provider immediately if you experience:
When in doubt, call your doctor. They would rather you call than wait.
Current version: 2.0 (January 2025)
Changelog:
We are committed to improving our algorithm as new research emerges. Any significant changes to our methodology will be documented here, and users will be notified.
Updates in progress: Continuous refinement of factor interactions, validation against emerging clinical data, machine learning integration for personalized risk assessment.
We're committed to transparency. If you have questions about how we calculate risk or want to discuss our sources, we're here to help.