Regarding OPK Sensitivity: OPK's are not like HPT's. Most women want HPT's that detect as little hCG as possible, because hCG is only produced during pregnancy*. Therefore, the more sensitive the HPT, the earlier it can detect pregnancy.
OPK's measure LH, which a hormone that is always present in the female body in some quantity. This hormone surges 12-48 hours before ovulation. In women of normal fertility, a "surge" (indicating ovulation is near) means at least 20 mIU/mL of LH is present. The vast majority of women experience a surge of 40 or more mIU/mL. Since a surge builds very quickly, a woman may go from an insignificant amount of LH to 40 mIU literally within an hour or so.
Therefore, an OPK that measures 20-40 mIU is adequate, and a more sensitive OPK (20 mIU) does not offer any real benefit over a less sensitive one (40 mIU.) It's possible that a woman may experience a "slower" surge, and "linger" at 20 before shooting up to 40 the next day. (This may differ from cycle to cycle for the same woman. It has no physiological significance.)
However, I am adding sensitivities to the chart below because some women may alternate brands of tests. I noticed that when I use a more sensitive OPK (20 mIU) I can detect ovulation approximately 36-48 hours before the fact; using a less sensitive one (30-40 mIU) I have only 24 hours' notice. If you happen to use 2 brands within the same cycle, this difference in sensitivity can prove confusing.
*A non-pregnant woman may have up to 2.5 mIU/mL of hCG in her system. This level is not detectable by home pregnancy tests and is, for HPT purposes, insignificant. Otherwise, hCG production is exclusive to pregnancy . . . in low levels (up to 9.5 mIU) during menopause . . . and with some rare forms of cancer. |
