Serial hCG Calculator
Enter two or more serum hCG values with the time each was drawn. The calculator gives the change over each interval, scaled to 48 hours, and compares it with the published curves for early pregnancy.
This is an educational calculator for clinicians. It compares numbers with published reference curves. It does not diagnose, it does not locate a pregnancy, and it does not replace transvaginal ultrasound or clinical judgment. hCG values alone cannot exclude an ectopic pregnancy.
hCG values
Use values in mIU/mL from the same laboratory. Nothing you enter leaves this page.
Assessment
hCG over time
Logarithmic scale. Both reference lines start from the first value. Values between the two lines fall outside both published curves.
Interval by interval
| Interval | Hours | Change | Scaled to 48 h | Doubling or half-life | Benchmark |
|---|
Before any number
ACOG Practice Bulletin 193 states that tubal ectopic pregnancy in an unstable patient is a medical emergency that requires prompt surgical intervention. Clinical findings come first:
- Hemodynamic instability, syncope, or signs of peritoneal irritation
- Increasing abdominal or shoulder pain
- Heavy vaginal bleeding
Any of these calls for immediate evaluation, whatever the hCG trend shows.
How the calculator works
- Scaling to 48 hours. Each interval is converted to an equivalent 2-day change, assuming steady exponential change across the interval: (later ÷ earlier) raised to the power (48 ÷ hours), minus 1. The published curves are expressed at 2 days, so intervals close to 48 hours give the most direct comparison.
- Rising values. Compared with the minimum (1st percentile) 2-day rise in symptomatic women with a pregnancy of unknown location who had an ongoing intrauterine pregnancy: 49% when the starting value is below 1,500, 40% from 1,500 to 3,000, and 33% above 3,000 mIU/mL (Barnhart 2016). The single conservative bound of 35% (Seeber 2006) is shown for reference.
- Falling values. Compared with the expected decline after a completed miscarriage, which ranged from 21% to 35% at 2 days depending on the starting value. A decline of less than 21% at 2 days, or less than 60% at 7 days, suggests retained trophoblast or an ectopic pregnancy (Barnhart 2004).
- Steep decline. In women with a pregnancy of unknown location and falling values, an 85% drop within 4 days or a 95% drop within 7 days ruled out ectopic pregnancy in the study and validation cohorts (Cameron 2015).
- Ultrasound threshold. In ultimately viable pregnancies, a gestational sac was predicted to be seen 99% of the time at 3,510 mIU/mL (Connolly 2013).
- Limits. In the validation cohort, 12% of ectopic pregnancies followed a curve that mimicked an intrauterine pregnancy or a miscarriage (Seeber 2006). A normal-looking trend does not exclude an ectopic pregnancy.