The optimum time for exogenous human chorionic gonadotropin to rescue the corpus luteum

Our purpose was to study the optimum time to administer exogenous human chorionic gonadotropin (hCG) to rescue the human corpus luteum during the luteal phase of normal menstrual cycles.

Groups of normally cycling women were given 4-day regimes of exogenous hCG by daily injection beginning 4 (Group A), 8 (Group B), and 12 (Group C) days after the midcycle luteinizing hormone surge. The hCG regime used was designed to mimic hCG levels following a spontaneous implantation. All subjects acted as their own controls in a preceding normal menstrual cycle.

Group A subjects exhibited patterns and levels of salivary progesterone concentration similar to those seen in the control cycles throughout the normal luteal phase. In contrast, subjects in both Group B and Group C demonstrated a rapid and sustained increase in progesterone production following the hCG injections. Furthermore, subjects in Group B achieved the highest mean peak progesterone concentrations and the total amount of salivary progesterone secreted was significantly higher than in the control cycles (P < 0.05). Although the mean luteal-phase length was greatest in Group C, the response of the corpus luteum was suboptimal, with a delayed rise in salivary progesterone.

These data show that the qualitative and quantitative response of corpus luteum to an early pregnancy-type hCG signal is maximal around the midluteal phase, coincident with the time of implantation.