[QUOTE=Shmead]I am not sure that the OPK would detect the trigger: the trigger is HCG, the same hormone the placenta produces during pregnancy. It’s a negative pregnancy test that confirms it is out of your system.[/QUOTE]
It actually does detect HcG since LH and HcG are so close together.
Heres a website dedicated to it:
Pee On A Stick ~ OPK’s as HPT’s
An OPK tests only for the part of the molecule that LH and hCG have in common.
So an OPK will turn positive when it detects either of the “identical twins”-- ovulation or pregnancy hormone.
The reverse is not true, however, because an HPT tests for the part of the molecule that is unique to hCG.
Therefore, a pregnancy test will turn positive only in the presence of hCG, whereas an OPK will turn positive in the presence of hCG or LH.