If you’re trying to get pregnant, you’re no doubt familiar with the acronym OPK. OPK stands for Ovulation Predictor Kit – the little test that’s designed to help you anticipate when you’re going to ovulate and when you’re fertile. Although they can be a helpful tool when trying to conceive, OPK tests are not without their drawbacks.
In this article, I’m going to discuss how these ovulation predictor kits work and how to use them correctly. I’ll also look at some of the downsides of using an OPK, and how learning the fertility awareness method can help overcome these problems.
- A bit about ovulation
- OPK tests – how do they work?
- OPK tests – how do I use them?
- OPK tests – 7 common pitfalls to watch out for
A bit about ovulation
In order to understand how these kits work, it’s important to first understand a little about ovulation.
Ovulation, put simply, is the release of a mature egg from one of your ovaries each menstrual cycle. Once this egg is released, it’s available to be fertilized by sperm, and conception can occur.
Contrary to popular belief however, this crucial event does NOT always occur on Day 14 of the menstrual cycle. The day of ovulation each cycle can vary from woman to woman and from cycle to cycle. In fact, in normal menstrual cycles, ovulation can occur as early as Day 8 or as late as Day 25 of the cycle.
Ironically, the day your egg is released marks the end of your fertile time, with your best chance of conception resulting from sex in the few days before ovulation (1) (2).
The purpose of OPK tests is to identify these fertile days preceding ovulation. Another extremely valuable alternative for detecting these fertile days is the Fertility Awareness Method (which I personally believe carries significant advantages over using an OPK – but more on this later).
OPK tests – how do they work?
So how does an OPK figure out when you’re going to ovulate? It all comes down to key changes in the levels of two of your reproductive hormones – estrogen and luteinizing hormone (LH).
These hormones are involved in the intricate and complex process that results in an egg being released from one of your ovaries each cycle.
Here’s a (very!) simple overview of how these hormones relate to ovulation and the use of OPK tests:
At the beginning of your menstrual cycle, in each ovary, about 15-20 eggs enter the final stages of development before ovulation. Each egg is encased in its own ‘sac’ or follicle. As they grow and mature, these follicles secrete the hormone estrogen (estradiol).
One follicle (and the egg it contains) ultimately dominates and continues to mature while the rest of the follicles degenerate and die. Levels of estrogen from this dominant follicle rise dramatically in the days leading up to ovulation until they reach a critical level.
This critical level of estrogen eventually triggers a surge of luteinizing hormone (known as the ‘LH surge’). It is this brief but dramatic rise in LH that triggers ovulation, causing the egg to be ejected from its follicle and released from your ovary.
An OPK is designed to detect these dramatically increased levels of either estrogen or LH (or both, in the case of the ‘Advanced OPK’ ) that occur just prior to ovulation.
OPK tests – how do I use them?
Urine based Ovulation Predictor Kits
Urine based OPKs come in a number of different formats – from basic paper strips through to cassettes with droppers, to a more fancy (but not necessarily any better) digital option. Regardless of the type, they are all designed to do the same thing – detect the surge in luteinizing hormone that occurs just before ovulation, as discussed above.
Depending on the type of kit that you use, you’ll need to either collect your urine in a cup, or hold a stick or test strip in your urine stream. Coloured bands (or lines) will appear on the stick or test strip to let you know whether or not the LH surge has started. Digital OPKs use easy-to-read symbols instead of coloured bands.
Tips to get the best out of your urine based OPK:
- Follow the manufacturer’s instructions closely as these can vary, depending on the kit
- Avoid using the OPK test the same way as you would a pregnancy test. A test band lighter in colour than the control band is NOT a positive result. The result is only positive if the test band is equal to or darker in colour than the control band.
- It is NOT advisable to use your first morning urine sample, as you would with a pregnancy test. This is because LH is synthesized in your body early in the morning and may not show up in your urine until later in the day. The best time to test is around 2pm, unless the OPK instructions specify otherwise.
- Once a positive result is detected, ovulation will usually occur within the next 24 – 36 hours, so make sure that you have intercourse during this time (although your peak fertile time may already be over – see the discussion on pitfalls below).
- If you are following the Fast Track to Pregnancy Program™ and charting your fertility, using an OPK is not necessary for detecting your fertile time. However, if you do choose to use an OPK test to provide additional information, this can easily be recorded on your fertility chart. Check the Charting FAQ in your program for details on how to do this.
Urine-based OPKs are generally highly accurate in detecting the LH surge, though interpretation of the results isn’t always easy.
Although using this type of OPK can be helpful if you’re trying to get pregnant, they are NOT foolproof and come with a number of pitfalls. For information on some of their limitations and how this can be overcome, see below.
Saliva based Ovulation Predictor Kits
A saliva based OPK detects the increased estrogen levels that occur before you ovulate.
As your estrogen levels rise due to the developing follicle in your ovaries, so too does the salt content of your saliva. When this saliva is put on a slide to dry, the salt crystallizes to form a pattern that looks like ferns. This ‘ferning’ pattern can be observed under a microscope.
A saliva-based OPK is basically just a small, transportable microscope that typically looks like a lipstick case. Saliva is placed on the in-built slide with a clean finger or by licking the slide.
Once dry, the saliva is observed through the microscope to see if there is a ferning pattern. This is compared with examples on the manufacturer’s instructions, to determine if you’re fertile or not.
Tips to get the best out of your saliva based OPK:
- Follow the manufacturer’s instructions closely as these can vary, depending on the kit
- Try to avoid getting air bubbles in your saliva sample
- Do NOT test after eating, drinking, brushing your teeth or smoking (but if you’re trying to conceive you’re not smoking right…?). The best time to test is the first thing in the morning.
- Ensure that you clean the slide in between tests without using soap or cleaning fluids.
- If you are following the Fast Track to Pregnancy Program™ and charting your fertility, using an OPK is not necessary for detecting your fertile time. However, if you choose to use an OPK test to provide additional information, this can easily be recorded on your fertility chart. Check the Charting FAQ in your program for details on how to do this.
Research has found a high correlation between estrogen levels and crystallization of saliva. Manufacturers claim 98% accuracy for the saliva-based OPK.
However, although they are quick, easy to use and relatively inexpensive, the saliva OPK tests don’t work for everyone and interpreting the slides can be difficult.
Although they can give more advanced warning of impending ovulation than the urine-based ovulation predictor kits, they still share some of their limitations as discussed below.
OPK tests – 7 common pitfalls to watch out for
Although OPKs can be useful if you’re trying to get pregnant, they are NOT foolproof and have a number of pitfalls.
A better way to gain an intimate understanding of your fertility is by learning how to correctly observe and interpret your basal body temperature and cervical fluid (the Fertility Awareness Method).
Used alone or in conjunction with OPKs, fertility awareness provides numerous benefits when you’re trying to get pregnant. This includes helping to overcome the problems experienced with OPKs (see the grey boxes below).
1. OPKs can get the timing of ovulation wrong
OPK manufacturers state that ovulation normally occurs between 24 and 36 hours after a positive test. But recent research (3) has found that ovulation can actually occur up to 6 days after the LH peak and up to 5 days before! This means that it’s possible to miss ovulation and your fertile days, if you’re relying on an OPK alone.
Charting your cervical fluid and BBT together, will give you a more accurate identification of ovulation day and your fertile window.
2. OPKs do NOT confirm that ovulation has occurred
Although both urine and saliva kits test for increased hormone levels prior to ovulation, they do not confirm whether ovulation actually occurred. An LH surge can sometimes occur without the release of an egg. Likewise increased estrogen levels are not always followed by ovulation.
Charting basal body temperature is a simple means of confirming whether or not ovulation actually occurred.
3. It is possible to miss the LH surge
Because the LH surge can be extremely brief, it can be easy to miss. For this reason, some women may need to test their urine twice a day. If you find that your OPK is never positive, you may just be missing the LH surge. However, it could also mean that you’re not ovulating.
Charting your temperature will help you determine if you’re just missing the LH surge, or not ovulating at all.
4. You may experience a ‘False’ LH surge
It’s possible to have a ‘false’ LH surge before the ‘real’ one occurs. This can result in timing intercourse too early and missing your true fertile time. Women with PCOS (Polycystic Ovary Syndrome) can continually produce false LH surges.
Charting your basal body temperature will confirm whether or not ovulation has followed your LH surge and whether or not you need to continue testing.
5. Ovulation Predictor Kits will NOT identify your day of peak fertility
Research suggests that your chances of conceiving are highest on the day or days that you produce your most fertile cervical fluid (3)(4). This peak fertile time can occur 2 or more days before ovulation. For this reason, an OPK can show a positive result after your peak fertile day has passed.
By observing and charting your cervical fluid, not only will you be alerted to your fertile days as soon as they start, but you’ll also discover your likely day(s) of peak fertility.
6. An OPK can miss some days of your fertile window
The fertile window is up to 6 days long (1)(2), with the last fertile day being the day of ovulation. Because ovulation can occur as little as 12 hours after the LH surge is detected, much of this fertile time can be missed.
Observing and charting cervical fluid will give you ‘advanced warning’ of impending ovulation and more time to plan baby-making sex.
7. Knowing when to test can be difficult (and can end up being expensive!)
If you have irregular cycles, it can be a challenge to know when to begin testing with an OPK. Because the day of ovulation can vary widely between cycles and a urine based kit typically contains a limited number of tests, one kit is sometimes not enough. This can soon become expensive.
Observing and charting your cervical fluid will let you know the appropriate time to begin testing.
8. Ovulation predictor kits will NOT alert you to a fertility problem
An OPK can only identify when you might ovulate and will not provide other valuable information about your fertility.
With the Fast Track to Pregnancy Program™ you will learn how your fertility charts can be used to identify potential fertility problems early, so that you can quickly get the help that you need.