Symptomatic patients with an early viable intrauterine pregnancy: HCG curves redefined.

Objective: To analyze the change in serial human chorionic gonadotropin (hCG) levels in women symptomatic with pain or bleeding who presented with nondiagnostic ultrasonography but were ultimately confirmed to have a viable intrauterine pregnancy.

Methods: The rise in serial hCG measures were modeled over time, with the start point defined in 2 ways: by last menstrual period and by date of presentation for care. Both semiparametric (spline) curves and linear random-effects models were explored. The slope and projected increase of hCG were calculated to define 99% of viable intrauterine pregnancies.

Results: A total of 287 subjects met inclusion criteria and contributed 861 measurements of hCG. On average, these subjects contributed 3.00 observations and were followed up for 5.25 days. A linear increase in log hCG best described the pattern of rise. Curves derived from last menstrual period and day of presentation do not differ substantially. The median slope for a rise of hCG after 1 day was 1.50, (or a 50% increase); 2.24 after 2 days (or a 124% rise), and 5.00 after 4 days. The fastest rise was 1.81 at 1 day, 3.28 at 2 days, and 10.76 at 4 days. The slowest or minimal rise for a normal viable intrauterine pregnancy was 24% at 1 day and 53% at 2 days.

Conclusion: These data define the slowest rise in serial hCG values for a potentially viable gestation and will aid in distinguishing a viable early pregnancy from a miscarriage or ectopic pregnancy. The minimal rise in serial hCG values for women with a viable intrauterine pregnancy is "slower" than previously reported, suggesting that intervention to diagnosis and treat an abnormal gestation should be more conservative.