Home pregnancy tests are testing for hcG.  Ovulation tests are testing for LH.  Chemically, these two hormones are extremely similar.  So similar, in fact, that hcG is mistaken as LH by ovulation tests.   (A home pregnancy test, however, does not mistake LH for hcG.)Given that ovulation tests are cheaper than home pregnancy tests, frugal peestick enthusiasts often want to know if they can simply use OPKs to test for pregnancy.  The answer?  Yes… BUT

  • a HPT will almost always pick up on a pregnancy before an OPK
  • only a HPT will confirm you are pregnant. A positive OPK could mean
    you are ovulating.    
  • this isn’t what OPKs were intended to do, so don’t blame the
    peesticks when they don’t bow down to your madness


(More acronyms, please!)

“I’m 10 DPO and have a second line on an OPK, but it isn’t positive.  Could I be pregnant even though the OPK was negative?”

You could be pregnant, but that OPK isn’t telling us much.  Many ttc’ers who use OPKs as HPTs find that they get a positive on a HPT before the OPK. Here is an example from the queen’s personal collection.   As you can see, the HPT is faintly positive at 9 DPO.  The OPK (on the bottom) isn’t quite positive yet, even at 10 DPO.

The OPK did indeed turn positive, but it was days after HPTs had already given a BFP:

“I’m 13 DPO and have a second line on an OPK. Could I be pregnant?”

The OPK must be positive (meaning the test line is as dark or darker than the reference line) to even be given consideration.  Many women always have at least some test line on an OPK.

Here are OPKs taken daily from the point of ovulation until the arrival of AF:

“My OPKs have been getting darker since 6 DPO. Could I be pregnant?”

The darkness of OPKs can vary for a variety of reasons, most not pregnancy-related. The amount of dye can vary from test to test.  More concentrated urine can cause a darker line to appear.  Daily variations in the amount of post ovulation LH can also cause the OPKs to appear as if they are getting darker.  Of course, yes, you could also be pregnant – but the odds of the OPKs telling you this before 12 DPO are just about nil.  (Unless you aren’t sure about your date of ovulation.) You are probably making your eyes cross and driving yourself into ttc-psychosis if you are comparing the darkness of one test to another.  Just step away from the peesticks for a few days, test again, and then compare. If they really are getting darker, your test at 10 DPO should be noticeably darker.   In fact, a HPT will give you a straight answer.