Ovulation Testing: How Ovulation Predictor Kits Work

Ovulation Tests - or Ovulation Predictor Kits (OPKs) - allow you to predict, with great accuracy, your most fertile time of the month. Easy to use, ovulation predictor kits can greatly increase your chances of becoming pregnant. To improve ovulation testing results, visit our Ovulation Test FAQ for testing tips. For more information on Ovulation and your Menstrual Cycle, click here.

Using Ovulation Tests to Predict Fertility

Ovulation is the defined as the separation of a mature ovum from the ovary after a follicle has been formed.

For many women, ovulation takes place midcycle, around cycle day 14. Of course, irregular cycles and countless other factors can contribute to ovulation taking place either earlier or later. That's why we use ovulation tests and chart fertility. In fact, "normal ovulation" can occur as early as day 8 or as late as three weeks into your cycle. When ovulation occurs is a coefficient of menstrual cycle length, so women with long cycles will ovulate later than women with shorter cycles.

To provide a brief overview of ovulation, the growth of an ovum takes place due to the influence of FSH - or follicle stimulating hormone. At ovulation, a surge in lh - or luteinizing hormone - facilitates the separation of egg from follicle. Here, cilia at the end of the fallopian tube move over and brush the ovary to help assist in the release of egg from follicle. For more on how an ovulation test allows you to predict this period of peak fertility, read on!

> How do OPKs work?
> How do I interpret ovulation test results?
> How do I determine when to begin testing?
> Ovulation Testing FAQ
> Fertility Monitor FAQ
> Capturing the Surge: Advanced OPK Suggestions!

Ovulation tests - or ovulation predictor kits (OPKs) - are excellent tools for predicting ovulation, a woman's most fertile time during her menstrual cycle. Unlike BBT charting, ovulation tests anticipate ovulation - not just confirm that ovulation has taken place. Visit Early-Pregnancy-Tests.com to see a photo gallery of positive ovulation test results.

Ovulation tests work by detecting luteinizing hormone (LH). Just preceding ovulation, women experience an "LH surge" - a sudden, dramatic, and brief rise in the level of luteinizing hormone. Ovulation tests detect the LH surge, allowing you to accurately predict when you will ovulate. A positive result on an ovulation test means that the woman will most likely become fertile over the next three days - with peak fertility at 36 hours following the LH surge.

How do OPKs Work? Luteinizing Hormone and Ovulation
How do ovulation tests work? At the beginning of the menstrual cycle, the body begins to produce follicle stimulating hormone (FSH). FSH facilitates the formation of a follicle on one of the ovaries. The follicle contains and nurtures the egg. When a follicle has adequately matured, a surge of Luteinizing Hormone (LH) causes the follicle to burst and release the egg into the fallopian tube - the moment of ovulation.

Throughout the menstrual cycle, a small amount of LH is produced - but during the middle of the cycle LH briefly and dramatically increases. Elevated quantities of luteinizing hormone facilitate ovulation - and OPKs detect this LH surge through anti-LH antibodies contained in the sensitive testing membrane of the test.

The LH surge is, alas, very brief - and in order to detect the LH surge, a woman needs to test at the right time of the month - and the right time of day. As LH is produced by the body in the morning, mid-afternoon is considered the ideal time to test.

Once the LH surge has been detected, successful fertilization is most likely to take place one to three days following the LH surge - with peak fertility at 36 hours post-LH surge. Since this ovulation "window" only opens once per month (and the unfertilized egg has a short 24-hour life-span) predicting ovulation accurately is very helpful when trying to become pregnant. Below, you will find information on getting the most out of your ovulation tests (and visit our Ovulation Test FAQ for more testing tips).

Using OPKs and Interpreting Ovulation Test Results

Ovulation tests come in two formats: test strips and midstream tests. To use the ovulation test strip, you fill a container with urine and hold the test strip in the container for several seconds. With midstream tests, you hold the test in your stream of urine. Both test formats are equally reliable. Always read ovulation test kit instructions carefully.

With most home ovulation testing products, the "reaction time" of the test is five minutes. At five minutes, you can interpret the tests. All tests have a "control" color band (or color line) that indicates whether the test is working or not. Also, the control band provides a color/intensity baseline by which to interpret the "test" band results. The "test" color band indicates a positive or negative result (please refer to the graphic below).

A positive result (indicating an LH Surge) is indicated by a test band that is of equal or greater intensity (equal or darker) than the control band. A negative result for the LH Surge is indicated when the test band is of lesser intensity (lighter) than the control band or cannot be seen. A negative result means the LH level of the urine sample is at or near its normal level and that the LH surge is not in progress. Remember, there is always some quantity of LH in your system, so a light color band in the test region is NOT an indicator of a positive result. 

How do I Determine when to Begin Testing?

To determine when to start testing, you must first do a little calculating. Use the Cycle Chart below to figure out when to begin testing for your LH surge.

First, determine the average length of your menstrual cycle. The length of the menstrual cycle is the number of days from the first day of menstrual bleeding to the day before bleeding begins on the next period. Determine the usual length of the menstrual cycle over the last few months. Then, refer to the Cycle Chart to determine on which day of the menstrual cycle to begin testing.

Your Cycle Length

Day to Begin Testing

21 days Day 5
22 days Day 6
23 days Day 7
24 days Day 8
25 days Day 9
26 days Day 10
27 days Day 11
28 days Day 12
29 days Day 13
30 days Day 14
31 days Day 15
32 days Day 16
33 days Day 17
34 days Day 18
35 days Day 19
36 days Day 20
37 days Day 21
38 days Day 22
39 days Day 23

We also offer an ovulation calendar to help estimate your most fertile time of the month based on statistical averages. However, regular ovulation testing most accurately predicts your fertile time period.

Read More About:

> Ovulation Test FAQ: Testing Tips and Tricks
> Pregnancy Testing
> Ovulation and your Menstrual Cycle
> Ovulation FAQ
> Clomid and Ovulation Tests
> Saliva Based Ovulation Predictors

. Ovulation Tests Instructions
> Ovulation Test Strips
> Ovulation Midstream Tests


I've been using OPK'S since last mth and my cycle is decreased by 2 days this month,that means i had 30 day cycle last mth(March 25th 2011) and this mth its 28 days.(apr 22nd 2011).When will I ovulate this cycle?

Hi I have a normal 27,28 day cycle never earlier or later I use opk and this month I first tested on day 10 and positive 7 days later and still very dark lines is this normal?? Thanks

Hi I have a normal 27,28 day cycle never earlier or later I use opk and this month I first tested on day 10 and positive 7 days later and still very dark lines is this normal?? Thanks

I too am Catholic and don't use birth control. I chart my cycles...there are tons of charting methods and even more insturctors to tell you how to do it. I am breastfeeding my youngest and my charting insturtor calls me ever two weeks. It is 99% effective and makes the divorce rate go down from 33% to 2% because its you and your husband working together to plan your family.


I am Catholic as well. I had a friend that had a similar problem with having children. Her and her husband went to the church and spoke to them about it. They gave the couple special permission to use birth control since it risked the mother's health. She wanted more childeren after her first two, but couldn't. Go to the church and see what they say if you don't want to go against the religion and practice exactly what they teach.

Hi I have had 4 c-sections in less then 8 yrs. I have been advised that having another would be too dangerous. The last c-section i had i hemorrhaged and had to be given medication to make my uterus contract. I am really trying to avoid pregnancy, however I Am Catholic and artificial birth control is against my religion. I am looking into natural birth control and was wondering if these ovulation PT's could help me?????

To Anon on Nov 30 with blocked tubes - You would still ovulate with blocked tubes, and thus would get a positive ovulation test. But the egg would not get fertilized or be able to travel to the uterous, because of the blockage. Surgury is usually required to fix blocked tubes, and there is no way to get pregnant naturally with both sides blocked. You will have to look into IVF, or get the blockages fixed.

what happens if i take 6 ovalation tests and they are all
postive does it mean that im vertile how many times a mnth

Itrying to becoming pregnent but my doctor told me your both tubes are blocked but Idid ovulation test it shows positive just Iwant to know this result It means the tubes are open thanks

I've used OPK's for 4 months now. The first month I detected Lh for 1 day and then nothing the next day. Month 2 was the same. Month 3 I detected a line but not quite as dark as the control line (so I assumed the next day it would detect Lh for sure) but when I tested the next day, it went back to very faint, so I assumed that I must have detected the Lh the day before (even though the line wasn't equally dark). This month, the first 2 days where faint then the next 3 days have been like the last month (dark but not quite the same as the control line) Can Lh go up and down before a positive result? Do these dark (but not quite the same) lines count as positive? I thought I understood what was going on in my body but now I have no clue and I don't want to miss my chance. Please help...

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Ovulation Calculator

Format: 4/18/2014
Increase your chances of getting pregnant! Our Ovulation Calculator will help you predict when you ovulate - your prime time for becoming pregnant.

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By TTC veteran and mother of two, Elizabeth Andrews.