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

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.

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.

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.

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.