Evidence-based gestational risk decay curve
Early pregnancy loss is a common biological occurrence, with roughly 80% of miscarriages attributed to spontaneous chromosomal aneuploidy (random genetic errors that occur during fertilization).
Rigorous prospective epidemiological studies (such as Wilcox et al., NEJM, and Ammon Avalos et al., Obstetrics & Gynecology) show that statistical risk declines rapidly with every passing day and week of embryonic development.
At 4 weeks (the time of a missed period), baseline risk is roughly 15% to 20%. By 6 to 7 weeks—once an ultrasound confirms fetal cardiac activity—the probability of carrying to term rises to over 96%. By 12 weeks, remaining risk drops to under 1%.
Worked example: Reassurance milestones
At 7 weeks gestation with ultrasound confirmation of a fetal heartbeat, the statistical probability of a healthy ongoing pregnancy is 96.5% (remaining risk ~3.5%).
At 10 weeks, term probability rises to 98.7% (remaining risk ~1.3%).
Miscarriage probability inputs
Gestational Age
Completed weeks and days of pregnancy.
Ultrasound Fetal Heartbeat
Confirmed embryonic cardiac activity significantly reduces risk.
CALCULATOR QUESTIONS
Early pregnancy miscarriage risk decay calculator questions
Why does seeing a heartbeat reduce miscarriage risk so dramatically?
The establishment of coordinated embryonic cardiac motion confirms that primary organogenesis is underway and that severe lethal chromosomal malformations that prevent cardiovascular development are absent.
Does heavy lifting or exercise cause miscarriage?
No. Everyday physical activity, routine exercise, stress, working, or sexual intercourse do not cause early pregnancy loss. Miscarriage is almost always caused by non-preventable genetic factors.