Ovulation Test: How do they work and what is its purpose?

By (gynecologist), (gynecologist), (embryologist) and (invitra staff).
Last Update: 04/15/2020

The ovulation test is a test used in women who are in the midst of getting pregnant, as it can help determine the fertile days of the menstrual cycle.

It consists of an indicator that measures the LH level in the urine, which increases when ovulation is about to occur.

These tests can be purchased at the pharmacy and are very easy to use: they work similarly to a pregnancy test.

What is ovulation?

Ovulation is a process that takes place during a woman's menstrual cycle: a mature egg is released into the fallopian tube and waits to be fertilized by a sperm.

Therefore, ovulation is considered the most fertile stage of the menstrual cycle, where the probability of conception during sexual intercourse is highest.

Remember that a woman's menstrual cycle usually lasts about 28 days if it is regular, during which the following phases or stages occur:

consists of the degradation of the endometrium in the form of vaginal bleeding when fertilization does not take place.
Follicular phase
a new ovarian follicle with an egg inside begins to mature to the right size.
Ovulatory phase
the mature follicle ruptures and expels the mature egg from the ovary into the fallopian tube.
Luteal phase
the egg is kept waiting to be fertilized and the endometrial thickness increases.

If you want to know in detail each one of these phases, we recommend you to continue reading here: the different phases of the menstrual cycle.

Calculation of fertile days

In a regular 28-day menstrual cycle, ovulation usually occurs about halfway through, that is, about 14 days after menstruation.

Therefore, it seems easy to calculate the fertile days if the woman keeps track of her periods. If you try for pregnancy, it is recommended to have unprotected sex during these days.

Ovulation tests are very useful tools for women with irregular cycles and regular cycles other than 28 days long.

On the other hand, women with an irregular menstrual cycle will have a greater difficulty in calculating the fertile days, since ovulation may take place earlier or later.

In any case, ovulation tests are a more reliable method to know which are the fertile days and, therefore, it is advisable to use them at the time of considering having children.

How does the ovulation test work?

The ovulation test, also called the LH test, is a test that determines a woman's most fertile days by measuring the LH hormone in her urine.

LH is a pituitary hormone (secreted by the pituitary gland in the brain) that begins to increase in concentration about 36 hours before ovulation, a time known as LH peak.

The ovulation test should be done daily to detect the highest level of LH. Once detected, sex is advised on the same day and the next day.

The average lifespan of an egg is about 24 hours. For this reason, it is important not to let this moment pass and that the sperm can meet it for fertilization.

If this encounter does not take place, the couple will have to wait until the next cycle to try for pregnancy again.


When doing an ovulation test, it is important that the woman takes into account the following indications:

  • Check the menstrual cycle if possible and start using the tests towards the end of the follicular phase. This will avoid unnecessary testing expenses.
  • Take the test every day at the same time.
  • Not having urinated in the 4 hours prior to the test.
  • The easiest way is to test the first urine in the morning, as it will be less diluted, but it can be done at any other time.

In addition to all this, it is important to note that it is not recommended that the male have many abstinent days before ovulation takes place. Sperm quality is greatly reduced when being several days without ejaculating.

It is best that abstinence is no more than 3 days while trying for pregnancy. It is also counterproductive to ejaculate several times a day, as the concentration of sperm will be diminished.

Types of ovulation test

There are different types of ovulation tests on the market depending on the medium. Below, we will discuss each of them:

Ovulation test on test strips
is the simplest and most economical format, like the Unitest brand. This is a strip that expresses its result in stripes after contact with the urine. For the test to be positive, the line corresponding to the LH must be marked with similar or equal intensity to the control line. If the LH stripe does not appear or is very clear, it will mean that the woman is on nonfertile days.
Digital Ovulation Test
the best known is the Clearblue. It consists of a more sophisticated format with easier to interpret results, because when the LH surge is detected, a smiley face simply appears on the test screen.

As already mentioned, when the ovulation test is positive, it is advisable to have sex on the same day and for the next two days, so that the encounter between egg and sperm is more likely to take place.

FAQs from users

Can ovulation tests also used as pregnancy tests?

By Elisa Pérez Larrea M.D., M.Sc. (gynecologist).

By detecting different types of hormones, ovulation tests could not be used as a pregnancy test.

An ovulation test is a test that helps to identify the time of ovulation, as this is the most fertile period in a woman's cycle. The test detects elevated luteinizing hormone (LH) in the urine.

However, a pregnancy test detects the hormone Beta-HCG (Human Chorionic Gonadotrophin), whose level increases in blood and urine progressively as pregnancy progresses.

What does a negative ovulation test mean?

By Lydia Pilar Suárez M.D., M.Sc. (gynecologist).

When a woman takes an ovulation test and the result is negative, she may think that something is not right and/or that she has problems ovulating. However, a negative ovulation test can also be due to the following reasons:

  • The woman does it with the first urine in the morning or without following the instrucitons correctly.
  • The patient is tested too far in advance of the LH peak (e.g. patient with long cycles).
  • The LH peak can be short (2 hours) and when the patient is tested, too much time has passed for the test to be positive. It is therefore advisable to do it twice a day.
  • The sensitivity of the test used is low and does not detect the specific LH peak of the patient studied.

Read more

By Zaira Salvador B.Sc., M.Sc. (embryologist).

This will depend on the length of each woman's menstrual cycle. The longer the cycle, the later the daily ovulation tests will be started in order not to waste the test.

For reference, in a 28-day menstrual cycle, the best thing to do is to start the ovulation test about 11 days after menstruation. Using cross-multiplication, if the woman has a cycle of 24 days, she can start with the tests at 7 days of the menstruation or, conversely, if the cycle is 32 days, she can start at 15 days of her period.

Ovulation tests are always positive, what does this mean?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

If the ovulation test is positive throughout the entire menstrual cycle, this means that the concentration of the LH hormone is elevated due to some alteration such as polycystic ovary syndrome (PCOS).

In this case, the woman will have to go to the gynecologist to check if she has any fertility problems and if she is ovulating correctly.

The same will happen if the ovulation tests are always negative, as this corresponds to anovulation problems.

Suggested for you

If you are interested in learning more about the process of ovulation, you can read on in the following article: What is ovulation?

There are other methods for detecting the fertile days, although they are less reliable than the ovulation test. You can find out more about this here: Use of cervical mucus as a fertility indicator.

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Authors and contributors

 Elisa Pérez Larrea
Elisa Pérez Larrea
M.D., M.Sc.
Dr. Elisa Pérez Larrea is a graduate in Medicine and Surgery from the University of Zaragoza and a specialist in Obstetrics and Gynecology from the University of Oviedo. She also has a Master's degree in Human Reproduction from the Complutense University of Madrid. More information about Elisa Pérez Larrea
Licence number: 203311163
 Lydia Pilar Suárez
Lydia Pilar Suárez
M.D., M.Sc.
Bachelor degree in Medicine and Surgery at the Universidad de Oviedo in Asturias. Specialization in Obstetrics and Gynecology at the University Hospital of San Carlos de Madrid. Master in Assisted Reproduction at the University of Rey Juan Carlos in collaboration with the Valencian Fertility Clinic IVI. More information about Lydia Pilar Suárez
Licence number: 64136
 Zaira Salvador
Zaira Salvador
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV
Adapted into english by:
 Romina Packan
Romina Packan
inviTRA Staff
Editor and translator for the English and German edition of inviTRA. More information about Romina Packan

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