NO, you don't ovulate if you are pregnant. You can't come up w/ $1 for an hpt at the dollar store? Can someone you loan the money?
If you don't even know where you are in your cycle, then this isn't going to be of much help to you but here you go:
OPK's as HPT's:
using an ovulation test to confirm pregnancy
Overall-- yes, it can be done. Ovulation predictor tests (known as OPK's because they are normally sold in a set of tests known as a "kit," thus the K) will show a positive result when a woman is pregnant, as well as when she's ovulating.
Specifically-- while it works most of the time, there are good reasons to avoid using an OPK as an HPT for diagnostic purposes. If you want to pee on any stick that will stand still
after you know you're pregnant, just for fun, have at it. But I would
not recommend using an OPK
in place of an HPT overall.
Reasoning-- OPK's detect LH (luteinizing hormone) which is the hormone associated with ovulation. Pregnancy tests detect hCG, the hormone associated with pregnancy. LH and hCG are, at a molecular level, nearly identical. hCG has a beta subunit, meaning it has an extra little "doodad." To use a stupid but easy to understand example, LH and hCG are identical twins, except that hCG wears a funny hat.
An OPK tests only for the part of the molecule that LH and hCG have
in common (the "face" or "body" of the identical twins.) Essentially an OPK is saying:
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 (the "hat.") So an HPT would say:
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.
Now, it's important to note that OPK's work differently than HPT's. A pregnancy test will develop 2 lines
only if hCG (pregnancy hormone) is detected. Thus, "a line is a line" when determining a positive HPT. OPK's work differently. An OPK has a "control" line and a "test" line, just like an HPT. Unlike an HPT, however, the mere presence of a "test" line does
not mean the test is positive. The test line must be
as dark as, or darker than, the control line to be a positive result (meaning that a
surge was detected, rather than the ordinary amount of LH usually found in your urine every day.)
This means that there is already some ambiguity involved in reading an OPK's results. Sometimes the line is almost as dark as the control line, but perhaps not
quite as dark. Sometimes only the edge turns dark, or the top half of the line is darker than the bottom.
Additionally, OPK's are not as sensitive as a lot of HPT's are. This means that, if pregnant, you are likely to get a positive HPT earlier than you would get a positive OPK.
Elaboration: a lot of women e-mailed me expressing surprise at this. Keep in mind that HPT's are often
more sensitive than advertised. First Response Early Result was found, in one recent clinical trial, to detect consistently as low as 12.5 mIU/mL of hCG, and sometimes as low as 4.5! OPK's are
never more sensitive than advertised (they are detecting a hormone "surge"; if they are
too sensitive they will turn positive from the normal all-the-time presence of LH in the female body.) The most sensitive OPK's on the market are 20 mIU, and some are sensitive to 30 or 40 mIU. OPK's may have a second line in the presence of less hormone-- the sensitivity refers to the threshold at which it turns positive.
So, if you are comparing a sensitive (20 mIU) OPK to some less-sensitive HPT's (sensitive to 25-50 mIU) then yes, it's true an OPK may turn positive before an HPT. However, the most sensitive HPT's available are
more sensitive than the most sensitive OPK's available.
Most importantly, OPK's are not purified as well as HPT's are. Therefore, they are more prone to "errors" and positives do not always mean that either LH or hCG was detected. In other words . . . they're simply cheaper, shoddier tests.
Finally, research has shown there are actually different
kinds of hCG. In some cases (most common in early pregnancy, or in pregnancies with chromosomal abnormalities) the hCG molecule may become "nicked" or "cleaved" (partially or completely separating into its alpha and beta units.) Ovulation tests may not recognize (cross-react) with all types of hCG molecules, and may be falsely negative during pregnancy. (An in-depth explanation of this is coming soon!)
At the end of the day, a positive result on an HPT
means you are pregnant. A positive result on an OPK could mean you are near ovulation, pregnant, or the test is picking up an entirely different hormone or element. Or it may be negative even if a woman is pregnant. With a positive HPT there is no doubt; a positive OPK may provide a clue, but doesn't really give you an answer
for sure.
So, my personal rule of thumb: use HPT's for pregnancy detection, and OPK's for ovulation.
If you already have your positive HPT and just want to "play" with tests, of course, that's something else entirely ;) So, for fun, ogle my OPK's. (They are Inverness brand cassette tests.) The one on the left is negative. It was taken at 9 DPO. I was pregnant, but my baby had not yet implanted (it was therefore too early for a positive test of
any kind.) The one on the right was taken at 13 DPO, the day
after I got a positive pregnancy test. The test line is clearly darker than the reference line, and is therefore positive.
Additionally . . . some women have experimented with the principle that an OPK, even if it's negative, will become increasingly darker if she is pregnant. (I did have a woman send me pics of this-- she took an OPK and HPT with the same urine during the "two week wait"-- 2WW-- and her OPK's did become increasingly dark. The HPT turned positive on the same day the OPK did. I am trying to find these pics because they were given to me before my old computer died . . . files are backed up, but not sure where! :-/ Anyway.) However, the question remains-- will an OPK always become increasingly dark if a woman is pregnant? Do increasingly dark OPK's always indicate pregnancy? In an effort to find out, I have been performing this experiment myself.
Remember: an OPK is only positive if both lines are equally dark (or if the TEST line is darker than the CONTROL line.) An OPK may show a faint test line in the presence of very little LH or hCG.
At 13 DPO, a new cycle began, confirming I was not pregnant. My OPK's did not become consistently darker, but some days were darker than previous days (e.g. 11 DPO was darker than the day before.) It does demonstrate that luteal phase LH levels fluctuate a bit and slight variations are normal.
Here is the next cycle's batch of tests. This time, I added breastmilk to an HPT to see if this is a method of early detection. Note: breastmilk tests are pink and streaky because of the milk's fat content.
Is that a faaaint positive on the HPT-with-pee I see?
Indeed! See the
HPT Showdown for a comparison of 15 brands with the same pee.
So, it seems in some cases, the OPK will NOT get consistently darker leading up to a positive HPT. The OPK did eventually become positive, but was not a helpful clue prior to the positive HPT.
So, I stand by my original assesment . . . OPK's for ovulation, HPT's for pregnancy.
Good luck, ladies!
(Our little positive test, Charlotte, was born August 10, 2006!)
http://www.peeonastick.com/opkhpt.html 
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