The 24-Hour Pattern of the Levels of Serum Progesterone and Immunoreactive Human Chorionic Gonadotropin in Normal Early Pregnancy*

Abstract

The purpose of this study was to characterize the levels of progesterone and hCG and the variability of those levels over 24 h in early pregnancy. Venous blood sampling was performed every 30 min during the first trimester of a subsequently normal pregnancy in 19 women. The variability in each progesterone and hCG data series was evaluated by three methods: 1) comparing the coefficient of variation (CV) of each individual hormone data set to the respective assay CV, 2) examining each data set for pulses, and 3) relating changes in hormone levels to the ingestion of a meal. The CV for each individual progesterone data set was greater than the assay CV (CV progesterone, 3.7%) in all subjects (range, 5.58-21.90%). The CV for each individual hCG data set was greater than the assay CV for hCG (CV hCG, 4.3%) in 17 of 19 subjects (range, 3.27-10.95%). Mean (+/- SE) progesterone and hCG peak frequencies were 2.4 +/- 0.3 and 1.7 +/- 0.3/24 h, respectively. When postprandial levels of progesterone were normalized to a percentage of preprandial levels, there were maximum decreases in mean progesterone levels of 15.4 +/- 2.6% and 13.1 +/- 1.9% 1 h after initiation of the lunch and dinner meals, respectively (P less than 0.05). Postprandial hCG levels decreased by 2.3 +/- 1.9% and 0.4 +/- 1.6% during this same time period (P greater than 0.05). These findings suggest that 1) both progesterone and hCG levels fluctuate during a 24-h period in early pregnancy; 2) this variability of both hormones is greater than inherent assay variability and can be resolved into a short term pattern of pulses, suggesting alterations in episodic secretion, metabolic clearance, or volume of distribution of the hormone; and 3) a portion of the variability in the progesterone time set may be due to the ingestion of meals.