Progesterone in the LP act as a heat inducing hormone, if I am correct, which elevates temperatures to incubate the egg. Hence why temperatures stay elevated when pregnant. I agree with DeeDeeAbi that some women do experience a brief temp dip with implantation but then it goes right back up and stay up. So, lets say you have a standard LP of 14 days, elevated temps pass this number can indicate pregnancy and also help you pinpoint a more accurate conception date. If you are not pregnant, Progesterone levels will decrease causing your temps to take a nose dive and trigger menstruation.