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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 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


hi, i need to ask about my cycle and ovulation test .i had cycle on 04-11-210. i started this test on 18april that is good time for ovulation test

Try the CLEAR BLUE EASY!!! digital and very easy to read!!!! I used the non digital kind many months and had similar problems reading it. It is a little more expensive but make a very big difference!

MY advice to everyone is to chart, if you don't know what charting is, then look it up. I have a really hard time telling when I ovulate because my period is not regular. The Ov Kit's help- but are also confusing cause they'll be "almost" positive for a number of days and sometimes never reach and actual positive. When using the kits along with charting, I have a better idea. The day after you ovulate, your temperature rises significantly. So I keep track and once my temp rises I'll know that I did in fact ovulate. But bodies are crazy precise, so you must be with your testing as well. Take your temp right when you wake up in the morning, don't even get out of bed. Always use the same thermometer, don't get up in the middle of the night to go to the bathroom- it'll mess it up. That will also mess up your ov kit. Ov kits should be used in the morning right when you wake up, that is when the LH surge will be the best to read. This all comes from me going to a fertility clinic for the last year, and charting and kittting and all of the junk. I am not pregnant yet- but I feel like I am at least close. If you don't think you are ovulating AT ALL- go to a fertility Dr. and they can figure out if you are or not, and get you on the appropriate hormones to help you ovulate.

I also have a longer cycle since going off of the pill... I found out I am ovulating late (around day 28), and am doing the OPK but not sure if it's very reliable since my cycle has been messed up after going off of BC. I have been doing it first thing in the morning but then read it's better to do it in the afternoon - when does everyone do it?

My fiance and i have been trying to become pregnant for over a year, and no luck. I do not have a regular period, i used to up untill 2yrs ago. Now i get my period every other month. Sometimes it is havier than others, and about 6months ago i began to have a clear discharge along with my period. The thing is that the discharge is actually like clear water. and sometimes i have to change my tampón every hour. Does this happen to any one else? Any one know what it is? Please help!

Hi! I am 41 and got married late in life. I was married 1 day before my 39th birthday. We got married in October of 2007 and became pregnant for the first and only time in January of 2009. Unfortunately, I miscarried in March. Well, recently we bought an opk and started using it on day 9. I am currently on day 16. I find these things hard to read. It appears that it could either be pos or neg, I'm not sure. I will have my dh look at it when he gets home. He is better reading these things than I. At any rate curiously enough I took my temp on day 15 and it was much higher than it was this morning. We made love last night. I also had a lot of mucus today, but it very well could've been semen. I will observe it again later. We have been trying to get pregnant again for about a year or so. Are these opk's hard to read for others and is my age making it harder for me to conceive a second time around?

hi..iam 24 years old and had my first child when i was 17..ans it was by c -section...every since then my periods have been crazy...well the problem is...that i ave been on xanax for 2 years now and my periods are longer apart now..any where from 31 to 39 days apart..some time they are so light that i just have to have a panty's 1-4-2010..and i didnt get my period for december....and i have tooken 2 preg. test both neg....i keep iam going to start..but nothing..and all so...i hope this is not to much info..but i have that thick clear iam i dont know what is going on...any advice would help...please..thanks for any one that helps

i havent had regualr period all my life how am i supposed to know how long my cycle is and all that when i can go two years without a freakin period any help would be greatly appreiated. sandra

i have a 28 day cycle, and i have been taking a clearblue fertility test and it keeps coming up negative! i started my period on the 23rd so i should be ovulating around the 6th/7th, and nothing yet!!! can someone help me? can people ovulate late?

The easy digital tests are extremely expensive.. But the first suggestion provided here is very helpful.. To use clearblue tests. I have the Cvs kit. Well, it might be simple for many. For some reason I am always confused when I need to interpret the results. After 5min it's right to check the test line.. That's when my tests have been negative till now.. (35 cycle .. Today is 15th) but when I chk the strip may be after an hour it gets darker.. Uff am tired.. I guess the test is rendered useless after 5min from dipping it in the sample. Good luck everybody!!!

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Ovulation Calculator

Format: 6/22/2018
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.