Diurnal variations in midluteal serum progesterone measurements.

The utility of a single midluteal phase progesterone (P) value has been questioned by studies that document pulsatile P secretion. In this study, fluctuations of P values during clinical sampling times were investigated. Significant differences were found between morning and afternoon mean P values and in the timed occurrence of clinically relevant P values. Despite reported pulsatile secretion, the impact of clinically significant fluctuations may be minimized by the use of timed sampling.