OPKs vs Ferning microscopes: Ovulation tracking made easy

So, if you’ve hit this page, you are probably thinking about using OPKs or a Ferning Microscope to track when you ovulate and help you optimise your timing of your baby dancing (sex) to get pregnant. In this article we will try and cover how OPKs will help you, how they work and how you use them. So, let’s get into it!

What is Ovulation?

What is Ovulation & Why should I track it?

Ovulation is defined as the release of the ova or ovules from the ovaries. So, what does this mean? Essentially, it means the point when an egg is released into the fallopian tubes (passage connecting the ovary where eggs are stored to the womb) and can travel towards uterus. When you are aiming to get pregnant you are then hoping for the sperm to meet the egg in the fallopian tubes and fertilise it, creating an embryo. Then hopefully when the embryo implants into the lining of the uterus (womb) and you are pregnant. If you wan’t more detail on exactly what ovulation tracking is then check out our All you need to know about ovulation tracking guide

What is an OPK?

An OPK (ovulation predictor kit) test, aims to give a window of between 10-36 hours where you will ovulate so that you can time sex to maximise chances of pregnancy. An egg only lives for around 24 hours once it’s released so there is actually a very short time frame where it can be fertilised by the sperm. Therefore, it can be helpful to know in advance when you might be ovulating so you can have sex and the sperm is waiting to meet the egg.

How does an OPK work?

OPKs works by tracking a hormone called luteinising hormone (LH) which surges and causes the release of the egg from your ovary, you can learn more about luteinising hormone here. The tests use a urine sample in a similar way to a pregnancy test.

They relatively cheap so can be a cost-effective way of checking when you are ovulating. The disadvantages being that some women find them a little difficult read, although we will show you how to below. Also, they are not suitable for women who have certain hormonal imbalances such as PCOS as they already have elevated LH in their urine and therefore the surge cannot be detected. Other conditions where OPKs should be avoided include: Turner’s syndrome, pituitary issues such as hypopituitarism and eating disorders.

How to use an OPK?

  • You should commence testing about 3-4 days before the midpoint of your shortest cycle (i.e. if you have a 29 day cycle, your midpoint would be 14 days so its recommended you start testing around cycle day 10 or 11; if you have a 34 day cycle your midpoint would be day 17 so you should start testing around day 13-14). I had a cycle length between 24-34 days so I would take the 24-day cycle, get my midpoint of 12 days and then take 4 days off so would start using them at day 8 of my cycle. You should continue to test each day until a surge of LH is detected.
  • When you are testing you should aim to test in the afternoon if possible. Most women have an LH surge in the morning which can then be picked up around 4 hours later in urine. If you can’t test in the afternoon for whatever reason then don’t panic though, as long as you try to test around the same time each day then you should be able to see your surge.
  • You should follow the individual instructions for the test you have purchased, but as a general guide:
    1. Collect your sample of urine in a clean dry cup
    2. Open your strip packet
    3. Insert your strip into the urine (ensure you insert it the correct way up, don’t insert your strip past the maximum marker).
    4. Remove strip from urine once the full test panel has absorbed the urine and lie flat on a piece of tissue.
    5. You will then need to wait usually 5-10 minutes to read the test. Usually you should not read it once 30 minutes has passed as the test will be invalid.
  • Ovulation strips are interpreted differently to a pregnancy test and therefore it is essential you understand how to read them. For an ovulation strip to be positive the test line must be equal to or darker than the control line. If the test line is lighter than the control line that is a negative test and there is not an LH surge. See image below for examples of the different test results you might see.
  • Once you get a positive LH surge you should have sex if you wish to get pregnant as you will likely ovulate in the next 12-36 hours. Remember you don’t necessarily want to have sex every day, sex every two to three days should maximise your chances.
  • Some women like to test both evening and night when they are approaching their normal fertile period or mid-cycle if you are not sure on your fertile period.
You need to be very specific in ensuring the lines are distinct when interpreting an ovulation predictor kit for a LH surge

What’s the best value OPK kit on the market?

This is again a relatively low-cost option although depending on your cycle length you may get through a lot of test strips. It is relatively convenient and if timed correctly you can get up to 12-36 hours’ notice of ovulation. Some more expensive tests such as the one below will also show you when your LH is beginning to rise as well as when you hit the peak of your surge to give you a longer fertile window, however, for most women the cheaper strips will be just as effective. Here are 4 tests we suggest for differing needs and budgets. The One Step and Easy@Home are budget friendly tests and I specifically have used the One Step tests for years with no problem. The Clearblue Digital test is a more expensive but easy read option as it does involve interpreting lines, you just get a smiley face when you have your surge. The Clearblue Advanced Test is the most expensive of the options but provides a smiley face when your LH is rising and then a flashing smiley when your LH is at it’s peak level (10-12 hours pre ovulation). However, if you are doing daily tests it is likely with time and experience you will be able to see the test line darkening day by day so will be aware if you are getting close to ovulation. As a general rule we would recommend sticking to the cheaper options, as depending on your cycle length you may be doing a lot of tests and there is no real additional value to the more expensive tests, unless you prefer an easier to read version.

What is a ferning test?

Another kind of ovulation test is called a ferning test which uses saliva on disc which you then examine with a microscope. You look for a fern like pattern to determine if you are close to ovulation. In general, you will likely ovulate 24-72 hours after you see a ferning pattern. This test is not perfect however, and you may fern outside your fertile time or when you are pregnant. Some men can even get a ferning pattern.

How does a ferning test work?

This essentially is looking for the increasing sodium (salt) levels in your saliva caused by rising oestrogen when you are ovulating which creates a fern like pattern when you look at your saliva under a microscope.

The ferning microscopes are a more expensive option that OPKs initially as you need to buy the kit, but most are reusable so could potentially be cheaper in the long run, if you were unfortunately needing to use it for a long time. They can potentially give an earlier indication of ovulation (up to 72 hours in advance) in comparison to OPKs, however, much of this will be dependent on your ability to interpret the results and as previously mentioned you make get ferning outside your fertile window. It should also be noted that not all women fern, some may fern but not on every fertile day and you may not always be able to see the fern. Again, certain women with hormonal imbalances which effect oestrogen levels such as PCOS should be cautious of results.

How to use a ferning test?

As ever, please follow the manufacturer’s specific instructions when using your ferning test. The below is a general guide to give you an idea of how it should be used. Most suggest you use the microscope every day of your cycle. It may take several cycles to start to see any pattern and it’s important to remember that a large number of women have a variation each month when they are fertile.

A simple infographic showing how to use a ferning microscope to test for ovulation whilst trying to conceive

What’s the best value ferning microscope on the market?

I personally chose not to use a ferning microscope for my conception journey so wouldn’t want to make a personal recommendation, however, my research, the Maybe Baby microscope appears to have the best reviews and appears fairly reasonably priced. You can learn more and purchase it from here via Amazon. There are slightly cheaper options but most have varying reviews so personally I wouldn’t recommend them but if you would like to look at an example of a more budget friendly option then you can one here from KNOWHEN.


So, which should you use? Obviously, this is a very personal choice and ultimately a decision you need to make. However, there are a few obvious advantages and disadvantage to both which may help you make your own decision.

As previously mentioned, OPKs are the budget friendly option initially, the ones I used were £4.95 for 30 (or $6.49 for 30 in the U.S.) and can be even cheaper if bought in bulk, whereas a ferning microscope is usually around £15-20 (or $30-40). However, once you have the ferning microscope most can be reused as many times as you need whereas obviously you will need to continue to buy OPK strips.

Neither unfortunately, are recommended options for women with hormonal imbalances such as PCOS as they rely on seeing rises in certain hormones which may be imbalanced and therefore you could get false readings. Both rely on interpreting your results but from my point of view I think interpreting a line on an OPK (deciding if it is darker than the control line) would be simpler than trying to find a ferning pattern through a microscope. You can also find apps for OPKs where you take a picture of your test and it interprets it for you if you are unsure.

It is also worth reiterating here that not all women fern and you can fern outside of your fertile period. Equally, the need to do the ferning test in the morning before you eat, drink, urinate or brush your teeth might be a hassle first thing when you need to get ready for work or then having to do it later in the day but avoiding those things for three hours before hand (I know I would get hangry if I couldn’t eat for three hours in the day). However, some women may find trying to do a urine test in the middle of the day, potentially while at work also inconvenient.

The other obvious option would be to do both and compare results, do their results match up and do you get an earlier indication with ferning microscope in comparison to OPKs, then you might prefer that option. If ferning doesn’t seem to work for you then OPKs might be the way forward.

Whatever you decide we wish you the best of luck and baby dust and hope that your wishes come true very soon. If you have used either OPKs or a ferning microscope let us know your experiences below to help other ladies. Which did you find most helpful?

Where next?

Luteinising Hormone – if you are thinking of using OPKs and want to learn more about how luteinising hormone works check this article out.

Ovulation Tracking – if you aren’t sure OPKs or ferning microscope is for you and want to look at the other ways to track your ovulation check out ovulation tracking article.

Menstrual Cycles – if you still aren’t sure how your menstrual cycle works and want to have a better understanding then this article is for you.

PCOS – Think you may have a hormonal imbalance and are curious about signs and symptoms of PCOS check this out.

If you found this artile useful then please feel free to use an image to pin it to help you find it later.


Which Method should I use to track my ovulation
Ovulation Predictor Kits vs ferning microscopes
Ovulation prediction made easy OPK's vs Ferning Microscopes

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