Beta-hCG Doubling Time Calculator
Evaluate early pregnancy viability and screen for ectopic pregnancy. Enter two serial quantitative beta-hCG values and the interval — get doubling time, percent rise, and clinical interpretation.
48h-equivalent rise
120.0%
Actual: 120.0% over 48h
Doubling time
42.2 h
Ratio 2.20×
Interpretation
Normal rise (≥66% in 48h). Consistent with viable intrauterine pregnancy. Confirm with TVS when hCG > 1500-2000 mIU/mL (discriminatory zone).
Plot hCG curves automatically
EasyClinic stores every quantitative hCG, draws the rise curve, marks abnormal trajectories in red, and triggers ectopic protocol reminders — built for early-pregnancy clinics.
Also Known As
Normal hCG kinetics in early pregnancy
- Up to hCG 1200 mIU/mL: doubles every 48-72h (≥66% rise in 48h)
- 1200-6000 mIU/mL: doubles every 72-96h
- >6000 mIU/mL: doubles every 96+ hours; trend less reliable, shift to TVS
- Peak ~100,000 mIU/mL at 8-11 weeks gestational age
Discriminatory zone (TVS)
- Transvaginal ultrasound should visualise a gestational sac when hCG > 1500-2000 mIU/mL.
- If no IUP visible at this level → strongly consider ectopic or non-viable pregnancy.
- Pseudosac (decidual reaction in ectopic) can mimic IUP — look for double decidual sign or yolk sac.
Clinical decision flow
- Rise ≥66%/48h + IUP on TVS: Reassure, routine antenatal care.
- Rise <35%/48h: Likely ectopic or failing IUP — surgical or methotrexate management.
- Rise 35-65%/48h: Repeat hCG in 48h + TVS. Do not assume viable IUP.
- Decline: Track to <5 mIU/mL. Watch for plateau (retained tissue, ectopic).
Frequently Asked Questions
▸How is doubling time calculated?
Doubling time (hours) = 0.693 × (hours between samples) / ln(hCG₂ / hCG₁). For a normal pregnancy this is 48-72 hours.
▸What rise is considered normal in 48 hours?
At least 66% rise (i.e. value goes up by two-thirds). A rise less than 35% is highly suspicious for ectopic or failing IUP.
▸Can a viable pregnancy ever rise slower than 66%?
Rarely — Barnhart 2004 redefined the lower limit to 53% rise in 48h for "minimal viable rise". But always confirm with TVS before reassuring.
▸What if hCG plateaus or falls?
Plateau suggests failing pregnancy or chronic ectopic. Falling hCG with persistent symptoms — rule out chronic ectopic. Falling to <5 mIU/mL — completed miscarriage.
▸When should I use methotrexate for ectopic?
After confirmed non-viable pregnancy (no IUP on TVS, declining or plateauing hCG, no fetal cardiac activity in adnexa). Per FOGSI 2021: hCG <5000, ectopic mass <3.5cm, no rupture, haemodynamically stable, no contraindications to MTX.
References
- Barnhart KT et al. Symptomatic patients with an early viable intrauterine pregnancy: HCG curves redefined. Obstet Gynecol 2004;104(5):975-81
- ACOG Practice Bulletin No. 193: Tubal Ectopic Pregnancy 2018
- RCOG Greentop Guideline No. 21: Management of Tubal Pregnancy 2016
- FOGSI Position Statement on Management of Ectopic Pregnancy 2021
Track every PUL patient automatically
EasyClinic logs serial hCG values, plots the rise curve, calculates doubling time at each visit, and flags abnormal trajectories — never miss an ectopic.
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