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Estimate pregnancy success probability from maternal age, weeks pregnant (LMP), prior miscarriages, and fetal heartbeat status. Shows how first-trimester risk falls week by week—especially after cardiac activity at 6–8 weeks. Pair with our HCG weeks calculator and gestational age calculator. Educational statistics—not obstetric diagnosis.
Last updated: June 5, 2026
Population averages help contextualize first-trimester anxiety. Bleeding, pain, or ultrasound concerns require your OB-GYN—not an online probability alone.
Cardiac activity often visible ~6–7 weeks on transvaginal ultrasound.
Default — age 32, week 8, heartbeat yes
98.2%
1.8% miscarriage risk
Age 30, week 6, heartbeat confirmed
96.4%
Major drop after cardiac activity
Age 28, week 5, heartbeat unknown
90%
Higher relative early risk
Age 38, week 12, 1 prior loss
95.4%
Late first trimester reassurance
Baseline age risk + prior loss modifier → multiplied by gestational week and heartbeat factors → miscarriage risk % (capped 0.5–95%).
Age 32 baseline: 12%
Prior losses: +0% → still 12%
Week 8 + heartbeat yes: ×0.15 → 12% × 0.15 = 1.8% miscarriage risk
Success probability: 98.2%
| Maternal age | Baseline risk | Teaching note |
|---|---|---|
| Under 30 | 10% | Lowest age-related baseline in this model |
| 30–34 | 12% | Slight increase; most pregnancies continue successfully |
| 35–39 | 18% | Elevated chromosomal aneuploidy risk with maternal age |
| 40–44 | 34% | Substantially higher baseline—specialist counseling common |
| 45+ | 53% | Highest baseline in this teaching model |
| Weeks LMP | Typical risk | Milestone |
|---|---|---|
| 3–4 | ~20–30% | Implantation; chemical pregnancy losses common |
| 5–6 | ~10–20% | Gestational sac era; cardiac activity not yet typical |
| 6–7 | ~5–10% (↓ with heartbeat) | Fetal pole / heartbeat may appear on TV US |
| 8–9 | ~2–5% (↓ with heartbeat) | Strong heartbeat confirmation—major reassurance milestone |
| 10–13 | ~1–3% | Placental development; risk falls sharply |
| 14+ | <1–2% | Second trimester—loss termed stillbirth, not miscarriage |
| Weeks | Heartbeat | Model effect | Teaching |
|---|---|---|---|
| 6–7 | Confirmed | Risk ×0.30 (~70% relative reduction) | Cardiac activity at 6–7 weeks substantially lowers loss probability |
| 6–7 | Not yet seen / unknown | Risk ×0.85 (slight reduction for time passed) | May need repeat ultrasound in 1–2 weeks |
| 8–9 | Confirmed | Risk ×0.15 (~85% relative reduction) | Strongest single reassurance factor in first trimester |
| 8–9 | Not yet seen | Risk ×0.50 | Absent heartbeat at 8+ weeks warrants urgent OB evaluation |
| Prior losses | Added to baseline | Teaching |
|---|---|---|
| 0 | +0% | No prior loss adjustment |
| 1 | +5% | One prior loss—most patients still have high success rates |
| 2 | +15% | Two prior losses—consider early OB follow-up |
| 3+ | +25% | Recurrent pregnancy loss threshold—specialist workup indicated |
| Finding | Urgency | Action |
|---|---|---|
| Light spotting or brown discharge | Usually not emergency | Call OB same-day or next business day; 25% of women have some first-trimester spotting |
| Mild cramping without bleeding | Usually not emergency | Rest, hydrate; call if worsening—uterine stretching is common |
| Fluctuating nausea or breast tenderness | Usually not emergency | Symptoms vary day to day in normal pregnancies |
| Bright red heavy bleeding with cramping | Call OB now / urgent care | Possible threatened miscarriage—needs evaluation |
| Sudden loss of pregnancy symptoms + bleeding | Same-day OB contact | May warrant hCG check or ultrasound—not always loss |
| Tool | Measures | Best for |
|---|---|---|
| Miscarriage risk calculator (this page) | Age, week, prior losses, heartbeat → success % | First-trimester statistical reassurance from milestones |
| HCG weeks calculator | Beta-hCG level → approximate gestational week band | Early pregnancy dating and doubling-time context |
| Gestational age calculator | LMP or ultrasound → weeks pregnant | Confirming how many weeks to enter in this tool |
| IVF due date calculator | Embryo transfer day → gestational age | ART pregnancies with non-LMP dating |
Education only. Not obstetric diagnosis, not emergency triage. Heavy bleeding, severe pain, or absent heartbeat at 8+ weeks require clinical evaluation—not calculator reassurance alone.
For expectant parents, nursing education, and first-trimester counseling context
Suggested hashtags: #Pregnancy #FirstTrimester #MaternalHealth #MedEd