Figure 2.

The requirement for luteal support during assisted conception. (A) In a downregulated cycle, exogenous hCG induces progesterone production, but in the absence of LH progesterone output declines earlier than during a natural cycle (dotted line). (B) In a conception cycle, endogenous hCG rises exponentially from LH+7 to maintain progesterone output (dotted line). (C) The endogenous hCG will rescue the corpus luteum in a downregulated cycle in assisted conception to maintain progesterone but there is a time of relative progesterone deficiency in the mid-luteal phase (Duncan 2017).