Objective: To investigate the hCG-time relationship in early pregnancy.
Design: Prospective, randomized study.
Setting: Pregnant human volunteers in a university-based clinical research environment.
Patients: Normal pregnant women with viable singleton pregnancies, conceived spontaneously or after ovulation induction.
Interventions: Vaginal ultrasound was performed, and blood samples were obtained for hormone parameters between 20 and 30 days after conception. The timing of the tests was determined by random assignment using sealed envelopes.
Main outcome measure: Serum hCG.
Results: The log hCG-time relationship was linear, both during the first 20 days and between 20 and 30 days after conception. The inclusion of a quadratic term in either regression was not statistically significant. The slopes of the two regression lines were also not statistically different.
Conclusion: For practical purposes, the hCG-time relationship in early pregnancy can be treated as log-linear, but short sampling intervals should be used if doubling times are to be calculated from paired samples.