The relationship of corpus luteum volume to relaxin, estradiol, progesterone, 17-hydroxyprogesterone and human chorionic gonadotropin levels in early normal pregnancy.

Our purpose was to characterize the growth pattern of the corpus luteum of early normal human pregnancy and correlate this growth with the corpus luteum hormone products: relaxin, progesterone, estradiol and 17-hydroxyprogesterone. A prospective study of seven patients was initiated at a mean gestational age of 4 weeks and 2 days. Corpus luteum volume and hormone concentrations were determined for each study patient every 48 h for a period of 2 weeks. Transvaginal imaging of the corpus luteum was performed by a single observer. Corpus luteum volume was calculated using the formula for an ellipsoid (4/3 pi abc/8). Correlation between corpus luteum volume and hormone concentrations was tested using Pearson's r. There was a mean three-fold increase in corpus luteum volume between 4 and 6 weeks' gestational age. Concomitantly, relaxin and estradiol concentrations increased, 17-hydroxyprogesterone declined slightly, progesterone remained stable and human chorionic gonadotropin (hCG) increased exponentially. Mean positive correlations were shown between corpus luteum volume and relaxin (r = 0.72), corpus luteum volume and hCG (r = 0.68), and hCG and relaxin (r = 0.82). However, there was a lack of correlation between corpus luteum volume and estradiol, progesterone and 17-hydroxyprogesterone. We have shown that a rapid increase in the corpus luteum volume occurs in early normal human pregnancy without a parallel rise in the classic corpus luteum steroid products. We interpret these findings to suggest that growth of the corpus luteum in early human pregnancy is largely derived from the proliferation of non-steroid secreting cells. The precise role of these cells in controlling steroidogenesis in this gland has yet to be defined.