Hi ladies,
I use a Persona machine as contraception which detects oestrogen, Lh and Uric acid (as a control). The machine physically "tastes" with a sensor for oestrogen, but the Lh comes up in a window just like on a OPK so i have effectively been using okp's for like a year.

I have found this - before ovulation for about 4-5 days i often have low levels of Lh, which show up but don't give a surge line. Most months i get a surge for 1 or 2 days, and this indicates ovulation as far as the machine is concerned - BUT some months, (and this is one of them) i have strong CM signs (i used the Billings ovulation contraceptive method for a year, so pretty well-up on cervixes etc!) and no surge. The machine hasn't indicated ovulation at all, but my signs indicate i am in my sterile luteal phase.

OPK's are okay, but i don't think doctors can predict reliably when ovulation will occur in relation to Lh. Some months i have a strong surge 2 or 3 days before i have the peak EWCM sign. Once i was on here, in fact, panicking because i had had sex on my first green day, and found i still had EWCM after the event. I must have JUST and no more missed ovulation that month!

I also read sopmewhere that if you are pregnant you get constant levels of Lh in your urine, as it supports the corpus luteum while the baby is getting set up in there. I never test after i have ovulated beyond a day or two, and usually if i do, i find i have faint lines, no positives, but Lh still there anyway.

I doubt any of this is much help - if i were you i would concentrate on the charting and the CM signs, they indicate best, as ovulation without any good CM is unlikely to result in pregnancy.

Hana