Beta hCG Doubling Time Calculator

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Category Medicine & Tests

First hCG Test (mIU/mL)

Second hCG Test (mIU/mL)

Time Elapsed

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About

Monitoring the rate of increase in human chorionic gonadotropin, or hCG, helps clinicians assess the viability of early pregnancies. A healthy embryo typically produces enough hormone to double the concentration in the blood every 48 to 72 hours. Deviations from this pattern may indicate ectopic pregnancy or miscarriage risks. This tool applies the exponential growth equation to two separate blood test results. It determines the precise doubling time in hours. Interpreting these results requires context regarding the initial absolute value. Higher baseline levels naturally double slower than lower ones.

Formulas

The calculation uses the logarithmic growth decay formula to solve for time T.

T = h × log(2)log(hCG₂) − log(hCG₁)

Where h represents the hours elapsed between the two tests. The percent change is derived using standard percentage formulas.

Reference Data

Initial hCG Level (mIU/mL)	Expected Doubling Time	Minimum Rise (48h)
< 1,200	48 to 72 hours	+60%
1,200 to 6,000	72 to 96 hours	+35%
> 6,000	> 96 hours	Variable

Frequently Asked Questions

Physiological saturation occurs as the pregnancy progresses. Once hCG levels exceed 6,000 mIU/mL, the placenta production capacity plateaus relative to volume. Doubling times over 96 hours are normal at this stage and ultrasound becomes the primary diagnostic tool.

This falls outside the standard 48-72 hour window for levels under 1,200 mIU/mL. While strict cutoffs exist, individual metabolic variations happen. Doctors often order a third test to establish a trend line rather than diagnosing based on two data points.

In early pregnancy before 8-10 weeks, a drop in hCG is clinically significant and usually indicates a non-viable pregnancy. However, verify lab errors or unit discrepancies before confirming. After roughly 10 weeks, hCG levels naturally peak and decrease.