Monday, July 13, 2009

Bibliosaur and the Great OPK Experiment

For the past couple of days, I've been running a bit of an experiment with my OPKs - and now it's time to reveal the results!

I got the impression from using OPKs during previous cycles that I seem to have an unusually short LH surge - a lot of women can get a positive OPK for two days in a row, but I never have. In fact, even when testing precisely every 24 hours as recommended, I've still managed to miss the surge completely. So this time around, I thought I'd try ramping things up a little and taking an OPK not once, not twice, but THREE times a day: morning, afternoon and night.

There were three things I wanted to try to determine with the Great OPK Experiment:
1. Exactly how long my peak LH surge is;
2. What time of day is best to catch it (most OPKs recommend testing at around 2pm, but the digitals say that although afternoon is best, you can test any time of day, as long as you test the same time of day each time);
3. As a sort of secondary test, I wanted to try to see exactly how the digital tests work. No real reason - I was just curious. I'd noticed during my previous cycles that the second blue line got darker as the test became closer to positive, just like a regular OPK strip, and I was curious to see if the digital interpreted the second line the same way I would. (Note: I tried googling, but couldn't find any official info about the digitals actually work - is it simply a digital "eye" that interprets how close the lines are in color/shade to each other, or do they test for the surge in some other way as well?)

So, I donned my sexy scientist outfit and went to work!

Experiment Day #1 - Cycle Day 9
I took the first two tests on CD9 - there was a second blue line on the afternoon test, but it was so faint that it barely shows in photos. I added arrows in the second image to try to make it more visible, and then polarized the third in Photoshop so that the line really shows up:

It's probably hard to see here, but at 8pm the second line was actually slightly darker in color than it was earlier in the day - but only very slightly:

Experiment Day #2 - Cycle Day 10
When I took the test first thing in the morning on CD10, the line was a bit darker than the previous day, although still pretty light - so far, the digital test seems to work the same as the traditional ones, maybe with some kind of digital eye comparing the blue lines and reporting back with a negative if they're not the same shade (or close to it):

But that afternoon - tada! A smiley face and two solid blue lines! The second line is lighter than what I'd interpret as positive on a traditional OPK - I'd probably have called this a negative if I was using a regular strip:

By 8pm that night, just 6.5 hours after the positive, the test was negative again - I was actually pretty surprised when I ejected the test to take a look at the lines, because they were more or less identical to the positive test I'd taken in the afternoon - this makes me think that instead of my digital eye theory, maybe there's a secondary way that the digital tests for the hormone (like how with digital HPTs, a negative test can still show two lines).

Experiment Day #3 - Cycle Day 11
At this point I figured that the surge had probably peaked and I wouldn't get another positive, but I decided to keep testing the next day anyway, just out of curiosity. The morning test was negative again and the second blue line very faint:

By the afternoon, it had gotten even lighter:

And by the evening, the second line had nearly faded away altogether and I resorted to polarizing the image in Photoshop again - the surge has definitely passed:

So, what answers did I get out of this?

1. Exactly how long is my peak LH surge? This completely confirms my suspicion that I seem to have an unusually short LH surge: less than 12 hours long, and probably even shorter than that (note: this doesn't affect ovulation, just my ability to get a positive OPK). This explains why I've managed to completely miss it during past cycles - I probably just tested a couple hours too early or too late.

2. What time of day is best to catch my surge? I don't care what the digitals say in the instructions about testing any time of day - the afternoon was clearly the best for me, and I'll be sticking to that in the future.

3. How exactly do digital tests work? A digital eye that compares the shades of the blue lines, or something else as well? I'm still not sure. The second line is definitely at its darkest when the surge peaks, but it's still lighter than what I'd call a positive on a regular OPK - plus it was just as dark on a negative as it was on a positive. This leads me to believe that there must be some kind of secondary test...or maybe the digital eye is just more sensitive than my human one and it distinguished a difference between the shades on the negative and positive that I couldn't. The moral of the story? If you're using a digital, trust the expensive smiley test, and don't worry about the lines!


  1. I'm impressed with your experiment and glad that you were finally able to get a positive OPK.

  2. This is a cool post and very informational, so thank you! I would just keep in mind that all OPKs are different. The ones I got online claim that even if there is a VERY faint second line that that is still considered a negative. I wouldn't have known that if I didn't read the directions thoroughly, I thought that was considered a positive, just like a pregnancy test. So interesting!

  3. OMG, Biblio... Can I just say I LOVE YOU? This sort of scientific experimentation (with cute outfit and all!) really gets me all fuzzy inside.

  4. Rock on! I love the "outfit"...if that doesn't sexify the BMS, I don't know what will! LOL! Glad you're learning about your body and your cycle so completely. Fascinating stuff, eh?'s hoping you catch that egg!

  5. OMG ty SOOO much for posting this info!! I am using the smiley's for the 1'st time this cycle and for some reason i am ovulating REALLY late! I am on CD 25 and my test stick from the smiley looks like your CD 10 9:00AM one!! My 1'st stick looked like your CD 9 1:30PM one!! OMG i hope i am finally getting close!!!! Still no smiley for me but i should get one tomorrow or the next day:)