Temporal refinement does not affect predicted human chorionic gonadotropin rise in early pregnancy

To examine the impact of validation and temporal resolution of estimation of hCG increase, because patients' hCG values are not obtained at precise daily increments or always in the same laboratory.

Retrospective cohort study of women presenting with nondiagnosed symptomatic first-trimester pregnancies who had serial hCG level measurements over time.

Not applicable.

A total of 171 women presenting from September 2007 to February 2010 with first-trimester pregnancy pain and/or bleeding for whom a normal intrauterine pregnancy was ultimately confirmed.

None.

Serial hCG values, time period between hCG measurements, hCG rise.

After data verification, 118 subjects contributing 327 values met inclusion criteria and passed data verification for analysis with improved temporal precision. The more precise data showed a steeper hCG rise, and the predicted 2-day hCG increase at the 1st percentile was slightly faster (1.68-fold vs. 1.56-fold) than the "raw" clinical data and previous models.

Data verification and improved temporal precision suggested a faster hCG increase in early intrauterine gestation than previously demonstrated. Because laboratory variation and temporal imprecision are common, these data demonstrate that current modeling of the expected rise of hCG in a normal gestation is valid and appropriately conservative in the determination of a nonviable gestation. No change in the minimal threshold for potential viability is recommended.