Corpus luteum response to exogenous HCG during the mid-luteal phase of the menstrual cycle

OBJECTIVE To assess a range of exogenous HCG regimes designed to simulate the endocrine environment occurring in biochemical, single and multiple pregnancies and to study the response of the corpus luteum to those regimes. DESIGN Prospective clinical study. PATIENTS Twenty-five normally cycling women aged 24-35 years were given one of four regimes of HCG injections designed to mimic the HCG concentrations found following spontaneous implantation. Regimes A, B, C and D were designed with starting HCG doses of 60, 140, 250 and 1000 iu, respectively. The daily HCG injections were then increased to give a doubling concentration every 30 h for regime A, every 27 h for regime B, every 24 h for regimes C and D. HCG administration was started on either days 7 or 8 after the LH peak. MEASUREMENTS Plasma HCG and progesterone concentrations, RESULTS Subjects given regime A failed to demonstrate any rescue of the corpus luteum despite low-detectable amounts of HCG in the circulation equivalent to those seen in some biochemical pregnancies. In contrast, subjects given regimes B and C demonstrated prompt increases in progesterone secretion immediately after the first HCG injection achieving HCG and progesterone concentrations in plasma similar to those seen in normal singleton pregnancies. Subjects given regime D also showed rapid rescue of the corpus luteum but this time achieved plasma HCG concentrations in the range normally seen in multiple pregnancies. All subjects in regimes a, C and D secreted significantly higher amounts of progesterone than those in regime A (P<0.001). However, despite the greater amounts of HCG used in regime D, the amount of progesterone produced was not significantly different from regimes B or C, CONCLUSIONS The exogenous HCG regimes used in this study successfully mimicked the hormonal environment found in biochemical, single and multiple pregnancies acid elicited appropriate corpus luteum responses.