Why is the Luteinizing hormone not measured instead of the progesterone concentration?

It is more difficult to measure the Luteinizing hormone in comparison to that of progesterone. The Luteinizing hormone release is also of a short period (1-2 days)(2,3).

The advantage of measuring the progesterone concentration is that it’s increase can be measured gradually throughout the estrus cycle. The ovulation peak occurs 2-3 days after the Lutenizing hormone peak, and the conception can take place 4-6 days after the Lutenizing hormone peak has taken place (3).