Male & Female Fertility Explained: What Factors Can Affect It?

By (embryologist), (gynecologist), (senior embryologist), (embryologist) and (invitra staff).
Last Update: 02/25/2021

Fertility is the ability to reproduce or procreate. In humans, male and female fertility differ on some points. One of them is the effect of age since a woman’s fertile period is limited with age.

Apart from the time aspect, there are other factors that can influence pregnancy, such as irregularities in the menstrual cycle, alterations in the function of the ovaries, or failures in sperm production.

Provided below is an index with the 8 points we are going to expand on in this article.

What factors influence fertility?

In humans there are many factors that determine the ability to procreate, both in men and women. Among the most important factors that influence fertility we find:

  • Reproductive age.
  • Ability to have sexual intercourse.
  • Health of both parents.
  • Semen quality.
  • Egg quality.
  • A woman's capacity to gestate.

Alterations in any of these points can lead to infertility problems in the couple and to difficulties in achieving an ongoing pregnancy.

Male Fertility

In the case of men, their fertility depends directly on correct sperm production or spermatogenesis, sperm quality, and the ability of the sperm to go outside.

Men are born with immature male organs and, with the onset of puberty, hormonal changes occur that allow sperm to begin to be generated. Inside the testicles, in structures called seminiferous tubules, sperm will be produced permanently. Subsequently, the sperm are transported through the vas deferens and expelled through the urethra by ejaculation.

Any alteration that influences any of these steps will affect, to a varying degree, male fertility.

Studies have shown that there may be a decline in male fertility with age, as some parameters such as sperm concentration or motility worsen. However, these changes in male fertility are not as dramatic as in the case of women, and it is possible to become a biological father even beyond the age of 50.

Female Fertility

Primarily, a woman's fertility depends on the quality of her eggs, as well as her ability to ovulate and carry a pregnancy to term properly.

A woman is born with all the oocytes she will have throughout her life. This means that a woman's egg supply is limited and is determined from birth.

Here are the main stages of female fertility:

  • Puberty: with the beginning of puberty, menstrual cycles begin and, therefore, menstruation.
  • Fertile period: During menstrual cycles, a series of follicles (the structures that contain the oocytes) develop inside the ovaries, as well as the full maturation and subsequent release of a mature egg. Physiologically, this process occurs every month until menopause approaches.
  • Menopause: as menopause approaches, cycles become more irregular or non-existent. Once menopause starts, which is usually around the age of 50, the female reproductive phase comes to an end. However, a woman's fertility deteriorates much earlier.

A woman's most fertile stage is in her early 20s. From the age of 30 onwards, their reproductive capacity decreases, and a more sharp decline occurs from the age of 35 onwards. By the time a woman reaches the age of 40, fertility worsens drastically, which makes the chances of getting pregnant naturally very low.

However, it should be noted that every woman has a different rate of development and these ages can change significantly.

In addition, there are other external lifestyle factors that can influence a woman's fertility.

A woman's fertile cycle

Although a woman is fertile throughout her menstrual cycle, the chances of getting pregnant vary throughout her menstrual cycle.

It is during ovulation (when the egg is expelled from the ovaries into the fallopian tubes) and the days around it when the probability of achieving pregnancy increases. The explanation is that during this period it is easier for the egg and sperm to meet and, therefore, fertilization occurs.

In a regular cycle, ovulation occurs on approximately day 14 of the cycle or, in other words, 14 days after the start of the last menstruation. Therefore, a woman's most fertile window is around that day. Taking into account the date when you expect to ovulate and increasing the frequency of sexual intercourse during that week, the chances of getting pregnant will increase during this period. Based on this information, ovulation and fertility calendars and/or calculators can be helpful in the search for pregnancy.

Despite this, the exact day of ovulation may change from one woman to another. There may also be variations in the same woman from one period to the next, especially if she has irregular menstrual cycles or ovulation problems. For this reason, this information is not always applicable and, on occasions, it is necessary to resort to other methods, such as ovulation tests or ovulation induction.

Fertility study

According to the World Health Organization (WHO), a couple is considered to have fertility problems when they are unable to achieve an evolving pregnancy after 12 months of unprotected sex. At that point, clinical studies would be indicated to determine what may be the reason for infertility.

In the case of couples in which the woman is older than 35 years, it is recommended that fertility studies be initiated if there is no pregnancy after 6 months of unprotected sex.

It is necessary that these studies are performed in a fertility clinic to make a correct diagnosis through a personalized fertility study of each member of the couple.

First, an extensive interview (anamnesis) must be performed so that the doctor can determine which tests will be necessary to identify the cause of the fertility problems.

In the study of male fertility, the most informative test is usually the semen analysis. This consists of evaluating a semen sample both microscopically and macroscopically.

In the case of women, both hormone analysis and antral follicle count by transvaginal ultrasound are the most common tests in the female fertility study.

Another test that is often requested is a karyotyping to rule out chromosomal abnormalities as a cause of infertility.

Depending on the results obtained, additional tests will be requested or the best treatment will be indicated to help the couple achieve their dream of parenthood.

FAQs from users

Until what age a woman is fertile?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Generally, men are fertile throughout their whole life, but a woman's fertility is limited. The childbearing age range in women declines eventually from puberty to menopause, usually between ages 15-49. The optimum time period for a woman to get pregnant is between ages 18-28.

As stated earlier, female fertility drops substantially from ages 35-37 onwards. Thus, while a 20-year-old woman has a 25% chance per menstrual cycle to get pregnant naturally, this percentage is reduced to 5% by age 40 onwards.

To what extent do environmental factors affect fertility?

By Javier Domingo del Pozo M.D., Ph.D. (gynecologist).

There are several environmental pollutants that have a certain impact, especially on male fertility, such as the direct exposition to heat that takes place at some work environments, exposition to radiations, some pesticides and dioxins, etc. Also, the chemical substance Bisphenol A (BPA), which has a negative impact on fertility and is used in the production of certain materials of daily usage (such as plastics, gums, PVC...) that are difficult to avoid, as they are present for example in the layer that covers the inside of food cans.

Should men freeze their sperm to preserve their fertility?

By Rocío Núñez Calonge M.Sc., Ph.D. (senior embryologist).

Although there exists different studies that relate an advanced age with fertility problems, actually it is still unclear.

In the testicle, sperm production is a permanent process, contrary to what happens in with egg production in females. This is the reason why, freezing sperm as a preventive measure is not so useful as in the case of egg freezing, since egg quality and quantity decreases from age 35 onwards.

Unless there exists a disorder that affects sperm production, in the case of cancer patients who are going to undergo chemotherapy or radiotherapy, or if the man undergoes some kind of surgery (such as in the case of vasectomy), freezing sperm for the future is not required.

How can the most fertile days to get pregnant be calculated?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

With an ovulation calendar or an ovulation test. The former allows you to find out the expected day of ovulation as long as you know the precise date of the latest menstrual cycle and the normal length of your cycles. Ovulation takes place halfway through the menstrual cycle, which means it occurs on the 14th day if it is a regular, 28-day cycle.

Ovulations tests measure a woman's LH (luteinizing hormone) levels when she is ovulating, as a surge occurs during this phase of the cycle.

Can sperm motility be improved?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Sperm motility can be increased with food supplements, a balanced diet, moderate exercise and avoiding toxic substances such as tobacco and alcohol.

More often than not, cases of low sperm motility can be improved by making these lifestyle changes. However, the most severe cases of low sperm motility may need in vitro fertilization (IVF) with ICSI to be able to conceive.

Can you increase your sperm count quickly?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Not exactly. Spermatogenesis, the process by which sperms are produced, takes around 2-3 months to finish. Taking this into account, an improvement in your sperm count will not happen earlier even if you follow a special diet, take supplements, avoid harmful habits, etc. It does not take place from one day to the next.

It should be clear that improvements depend on the origin of your problem. If the reason why your sperm count is low is caused by agents that are not related to your lifestyle, your sperm count is not going to improve.

If I preserve fertility will I remain fertile?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Yes, fertility preservation does not affect fertility. However, the chances of achieving pregnancy naturally will be reduced over time due to the depletion of the ovarian reserve with age, regardless of whether fertility has been preserved or not.

Therefore, the advantage of fertility preservation is that a pregnancy is possible by assisted reproductive technology if fertility has been previously preserved, even if the ovarian reserve is already compromised.

Because of this, fertility preservation should be done at a young age (especially in the case of women, since age has a more damaging effect on female fertility) or prior to treatment, for example oncological, which is expected to damage fertility (both men and women).

Can the results of fertility tests vary over time?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Yes, but it depends on what is causing infertility. Nonetheless, results can vary from test to test, either for the better or for the worse, as long as it is a case of temporary and treatable infertility.

A man's sperm quality can be improved if, for example, stress or an infection was the reason behind it. And the same applies in cases of women suffering from a hormonal imbalance.

However, when infertility is a consequence of cancer treatments such as chemotherapy or radiotherapy, or is caused by non-obstructive azoospermia (zero sperm count) or early menopause, we are talking about permanent infertility and improvements cannot be achieved naturally.

Does lifestyle have an impact on fertility?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Yes, factors such as diet, body mass index, sedentary lifestyle, caffeine, tobacco, alcohol, drugs and exposure to toxins and radiation can affect male and female fertility.

A varied diet, weight control to have an adequate body mass index, moderate (not excessive) exercise and avoiding bad habits such as increased caffeine consumption, smoking, alcohol and other substances are recommended to avoid damaging fertility, both male and female.

Is there a way to preserve fertility naturally?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Yes, through egg and sperm cryopreservation. Although it is uncommon among men, it is becoming increasingly popular in women due to causes such as delayed motherhood and the sharp decrease in fertility levels with age. In these cases, freezing the eggs at a young age to use them for later pregnancy is advisable.

Cryopreservation is a method that gives men and women under cancer treatment the chance to become parents. Both radiotherapy and chemotherapy destroy egg- and sperm-making stem cells, and increase the likelihood for passing a genetic abnormality to offspring. This is the reason why cancer patients should choose to freeze their gametes before getting started with the treatment.

Can a man's fertility be damaged after chemotherapy?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Yes, treatment with chemotherapy can even cause irreversible infertility, due to cytotoxic effects on spermatogenesis.

It is therefore recommended that the male freeze several semen samples before the start of treatment. This measure, known as fertility preservation, will allow him to use these semen samples (prior to the damage caused by the chemotherapy treatment) to be able to seek a pregnancy by assisted reproduction techniques in the future.

Suggested for you

If you want to know more about male infertility, you can visit the following link: What Causes Male Infertility? - Symptoms & Treatment.

You can find more information about fertility tests in the following links: Male Fertility Testing - How Do You Know if You Are Infertile? and Female Fertility Tests - How Do You Know if You Can't Get Pregnant?

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Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo
 Javier Domingo del Pozo
Javier Domingo del Pozo
M.D., Ph.D.
Bachelor's Degree in Medicine from the University of Alicante. Specialist in Obstetrics & Gynecology via M. I. R. at Hospital Universitario Materno-Infantil of Canarias, Spain. PhD in "Human Reproduction and Female Reproductive System Pathology" from the University of Las Palmas de Gran Canaria. Currently, he is the Director of the clinics IVI Las Palmas and IVI Tenerife. More information about Javier Domingo del Pozo
License: 353504174
 Rocío Núñez Calonge
Rocío Núñez Calonge
M.Sc., Ph.D.
Senior Embryologist
Bachelor's Degree in Biological Sciences from the Complutense University of Madrid. Wide experience in the scientific field, particularly as lab director. Currently, she is the Scientific Director of Clínica Tambre. More information about Rocío Núñez Calonge
 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-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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