Ovulation Predictor Kits vs. Fertility Monitors

If you’ve been trying to conceive for a few months without success, you might want to consider using an ovulation test or a fertility monitor.

These devices can help you track your ovulation cycles and maximize your chances of conception. But like many women, you might be wondering which of them–an ovulation predictor kit (OPK) or a fertility monitor–would be a better option.

Why Use OPKs or Fertility Monitors? 

Before delving into this, do you know when you ovulate? If your answer is “No”, it’s not surprising. In fact, a survey showed that up to 72% of women did not know their natural fertility signs

If you’re not sure about the signs your body is sending to indicate that you’re ovulating, an OPK or fertility monitor can help you understand what stage of the cycle your body is at, thereby giving you an idea of when your chances of conception are high.

To understand the hormones that are produced during what part of your cycle, you can read my previous post that explains how your menstrual cycle works

OPKs and fertility monitors pick up these hormones and can help​ you determine when you’re most likely going to ovulate. Note that these devices do not confirm that ovulation occurred, but only give you an indication of when to expect when it will happen. 

Some women use these data in conjunction with a basal body thermometer to help them pinpoint ovulation. Contrary to OPKs and fertility monitors that predict ovulation, your basal body temperature measurements will tell you that it occurred.

So, you can have a luteinizing hormone (LH)​ surge, which will be picked up by an OPK or fertility monitor, but for some unknown reason, your body doesn’t release an egg.  

Types of OPKs

There are basically two types of OPKs: urine-based and saliva-based.

A. Urine-Based Ovulation Test Kits

These kits detect the presence of LH or both LH and estrogen in urine. During the first phase of the ovarian cycle, the level of LH increases and when it peaks, a mature ovum is released from your ovary within 12–36 hours.

Although you’ll always have a small amount of LH, the hormone builds up and quintuples in the days leading up to ovulation.

Your fertile window begins before your LH surge and sperm can survive for up to 5 days in fertile cervical fluid, giving you only six days during your cycle when you’re most likely to conceive after unprotected intercourse. 

1. Standard OPKs

  • These are the cheapest options to help you predict ovulation.
  • They are sold at your local drugstores or online (Amazon). Some brands sold at drugstores can be quite expensive, so most women prefer to purchase cheap OPKs (the Wondfo brand, for example) online. Read more about the top-ranked standard OPKs here

2. Digital OPKs

  • These are not very different from standard OPKs, as they also detect the presence of LH in urine. See our top choice here.
  • The main difference between digital and standard OPKs lies in the manner in which the results are read. More about the results a few paragraphs down.

3. Advanced Digital OPKs

  • These OPKs detect both LH and estrogen in urine.
  • Because they also detect estrogen, which increases several days before LH, these devices give you a better heads-up that you might ovulate soon. 

Learn about the best products in this category here.

B. Saliva-Based Ovulation Tests

As mentioned earlier, estrogen increases and reaches a point where it causes a rapid increase in LH (also known as the LH surge), resulting in the release of the mature egg.

As your estrogen levels increase, the amount of salt in your saliva also increases. When your saliva dries up, it causes the formation of a fern-like pattern, which can be observed under a microscope. 

Saliva-based ovulation kits make use of a small microscope that detects ferning in your saliva during the ovulation phase of your ovarian cycle. 

Here are our best selection of recommended saliva-based ovulation test kits.

Types of Fertility Monitors

There are several types of fertility monitors: urine-based, perspiration-based, and saliva-based.

A. Urine-Based Fertility Monitors

These monitors detect both estrogen and LH like advanced OPKs. Estrogen levels start to rise a few days prior to LH release.

By detecting an increase in estrogen, these fertility monitors can give you several days notice of an imminent LH surge and therefore several days notice that you might likely ovulate. You can plan to start having intercourse when it detects a rise in estrogen and continues through ovulation to increase your chance of getting pregnant. 

These fertility monitors also have an added advantage in that they store your data from your past cycles and use this information to tell you when to start testing.

These devices are more expensive than OPKs and can cost between $110 and $400+ but might be worth it if you’re struggling a lot to understand your body using natural methods and standard OPKs.

Read my review of Clearblue fertility monitors, with and without touchscreen here.

B. Perspiration-Based Fertility Monitors

These use your perspiration to track your body chemistry to identify the most fertile days of your cycle. 

An example of this type of monitor is the OV-Watch Fertility Predictor Value Kit, which you can wear like a watch while you sleep or go about your daily activities.

Unfortunately, this product is no longer available. 

C. Saliva-Based Fertility Monitors

These monitors work by detecting fluctuations in electrolyte levels in your saliva, which are caused by an increase in your estrogen levels.

An example of this type of monitor is the OvaCue Fertility Monitoring System, which comes with a sensor that you have to place under the tongue. Read our review of this monitor here

Reading Your Results

It can get pretty confusing to read the results of standard OPKs, let alone knowing what time of the day to test. 

So, when is the best time of the day to test for ovulation?

You can use standard and digital OPKs at any time of day, provided your urine is not diluted. Nevertheless, it is best to not use these OPKs in the morning given that your LH typically starts to peak in the early hours of the morning when you’re still asleep and may not detectable in your first morning urine.

You might miss your LH surge if you test early in the morning since the level may not be high enough to be picked up by an OPK. It is usually preferable to test in the late morning or early afternoon; however, you should read the manufacturer’s instructions to obtain the best results.

  • Tip 1: Since standard OPKs such as those sold by Wondfo are quite cheap, you can start testing at around midcycle, say cycle day 10 or 11 (if you have an average cycle length of 28 days), or a little earlier if your cycle is shorter, and tape the test sticks sequentially to a lined notecard. This way, you can see the test line becoming darker, and use this to know when to start testing more frequently. This worked very well for me when I started using them initially.

With advanced digital OPKs and urine-based fertility monitors, it is advisable to read the instructions provided by the manufacturer. In most cases, these tests should be performed using first morning urine.

However, some manufacturers might recommend using afternoon urine, so it is always best to refer to the product instructions for details.

Standard OPKs

Most women complain that they have difficulties telling when a test is positive. This is mainly because they cannot really tell when the test line is as dark as the control line.

If you’re unsure about what to look out for on a standard OPK test, the video below will give you an idea.

As you can see, assuming you watched the video, your result is positive when the test line (close to the dipping end of the stick) is as dark as the control line (closer to the handle).

Do not worry if you see two lines every time you test. What you should look at is the intensity of the test line with respect to the control. 

  • Tip 2: You can document your basal body temperature (BBT) while using OPKs, and once you get a positive ovulation test, you should start having intercourse until your BBT readings indicate a sustained change in temperature. In many cases, though, manufacturers advise users to stop testing after their first positive OPK, but it's up to you to keep testing until you observe a sustained shift in your BBT readings.

Digital OPKs 

These are much easier to read than standard OPKs. A plain open circle is displayed if the result is negative, whereas a positive result is displayed as a smiley face.

The smiley face is an indication that your LH is peaking and you should plan romantic interludes since ovulation is imminent.

Saliva-Based Ovulation Tests

You can read the results five minutes after placing a sample of saliva on a lens. If ovulation has occurred, or is imminent, you will see a ferning, crystal-like pattern through the eyepiece of the microscope, which comes in the kit.  

The video below demonstrates how the Fertile Focus saliva-based ovulation test can help predict your peak fertile days. 

Advanced Digital OPKs and Urine-Based Fertility Monitors 

Similar to digital OPKs, advanced digital OPKs and fertility monitors use a smiley face system. However, the system is a little different as described below.

Open circle: The levels of both estrogen and LH are low. 

Flashy smiley face: Estrogen levels have started increasing, implying that your LH level will peak soon.

Solid smiley face: This occurs when your LH surges, implying that you’ll likely ovulate within 12–24 hours.  

The video demonstrates how to use and read the results of the Clearblue Fertility Monitor.  

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I’m Princila, founder of Check Ovulation and a proud mom of two. I’m an alumna of James Lind Institute. After working in clinical jobs, my passion for writing took its toll, and I ended up switching careers to work in the medical publishing industry. I also have a passion for healthy food, which prompted me to take several online courses in nutrition and health offered by Wageningen University. (I still haven’t completed the courses thanks to my busy mommy schedule!). When I’m not writing/editing scientific and medical manuscripts or taking care of my family, I use my free time to research, learn, and write about healthy living. I have also authored a few books in the self-help niche using the pen names Princila Murrell or PN Murray.

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