Fig. 3.

Progesterone reference ranges from three different sources^1,2,3 for the follicular (F) and luteal (L) phases of the menstrual cycle. All sources are clinical reference ranges from different National Health Service Trusts in the UK and are based on the manufacturers' laboratory reference ranges. This figure illustrates the differences in the reference ranges for each of the two prevailing progesterone phases of the eumenorrheic menstrual cycle and suggests that additional context is required (e.g., blood sample taken on day two of bleeding, thus allowing the comparison with the follicular range; blood sample taken seven days after ovulation was denoted by a positive urinary luteinising hormone test kit, thus allowing comparison with the luteal range values)