Infertility and BMI: How does Weight affect Fertility?

By (gynecologist), (embryologist), (embryologist) and (invitra staff).
Last Update: 09/19/2019

Unhealthy lifestyles and habits have a big influence on the fertility of both men and women.

Among these factors, poor nutrition, obesity, and other eating disorders contribute to the fact that more and more couples are forced to resort to assisted reproduction in order to have children.

BMI calculation

Body Mass Index (BMI) is a measure that relates a person's weight to their height and serves to know if we are within a healthy weight range.

To calculate the BMI, simply use the following mathematical formula: Weight (lbs) x 703/height (in²).

The World Health Organization (WHO) considers the nutritional status of a human being to be healthy when the BMI is between 18.50 and 24.99.

Below, we show the entire classification of nutritional status according to each person's BMI:

BMI < 18
BMI 18-25
BMI 25-30
BMI 30-45
BMI < 45
Severe Obesity

It is recommended that all women seeking pregnancy have an adequate BMI in order to avoid not only fertility problems but also obstetric complications that could put the future baby's health at risk.

Effects of overweight and obesity

Nowadays, Overweight and obesity have become one of the world's major health problems, as people's excess weight increases the risk of cardiovascular disease, hypertension, and diabetes.

In addition, obesity also greatly affects the reproductive capacity of couples. On the one hand, it reduces the possibility of conceiving naturally and, on the other hand, it reduces the probability of success of an assisted reproduction treatment.

This is because body fat has an effect on estrogen production and blocking gonadotropin-releasing hormone (GnRH), which in turn is responsible for regulating pituitary function and the release of FSH and LH hormones.

As a result of all this hormonal dysfunction, both the menstrual cycles of women and the sperm production of men are altered.

In the following sections, we will discuss in more depth the effects of overweight and obesity on infertility.

In women

The excess of oestrogens in overweight women affects the entire hypothalamus-hypophysis-ovarian reproductive axis and causes alterations such as the following:

As for assisted reproduction treatments, obese or overweight women also have a lower rate of gestation due to a multitude of problems that may arise during the cycle:

  • Resistance to gonadotropins, so they will need a higher hormonal dose in ovarian stimulation
  • Follicular asynchrony and obtaining immature eggs
  • Low response to stimulation
  • Increased risk of cycle cancellation
  • Increased risk of complications during follicular puncture
  • Lower fertilization rate
  • Worse embryo quality

In men

Obesity is also a cause of male infertility, since it causes alterations in semen and other dysfunctions in the reproductive system. These are discussed below:

All of these abnormalities lead to a higher rate of fertilization failure and implantation failure, as well as an increased risk of miscarriage.

If you want to read more about the effect of being overweight on male fertility, we recommend you enter the following article:

Effects of underweight

Drastic weight loss or being underweight with a BMI of<18 can also influence the fertility of men and women.

This weight loss may be due to dietary restrictions, such as anorexia, or increased energy demands on the body, for example, due to illness or intense physical exercise.

Low weight also affects hormone production and metabolism. Therefore, it is common for the following alterations to appear in a woman's menstrual cycle:

  • Irregular menstrual cycles
  • Amenorrhea
  • Endometrial alterations that prevent implantation

As for men, low weight also implies sperm alterations, such as reduced concentration and reduced sperm motility.

Recommendations for getting pregnant

Couples who have an altered BMI and are in search of gestation are advised to consult a nutrition expert in order to achieve optimal weight and a healthy pregnancy.

Obese patients should also visit the endocrinologist for stricter follow-up.

In general, a moderate loss of 5-10% of initial weight, through dietary education and physical exercise over six months, may be sufficient to restore reproductive function and achieve a natural pregnancy.

Next, we are going to give some essential advice and recommendations to achieve an adequate BMI and a correct distribution of body fat:

  • Complete lifestyle changes
  • Having a healthy and balanced diet based on the intake of vegetables, fruits, fish, legumes, etc.
  • Taking folic acid supplements
  • Moderate excercising
  • Avoiding exposure to toxic agents and the consumption of substances such as alcohol, tobacco, caffeine, etc.

In short, all sterility problems resulting from excessive thinness or overweight can be reversed by simply modifying lifestyle and eating habits.

By regaining normal weight, it is possible to stabilize hormonal imbalances again and thus restore male and female fertility.

In assisted reproduction treatments, weight loss also helps women respond better to ovarian stimulation and ovulation induction drugs.

Besides, maintaining a healthy weight not only reduces infertility and the risk of complications during pregnancy but also contributes to overall health and improves self-esteem.

FAQs from users

How does one's lifestyle affect fertility?

By Joel G. Brasch M.D. (gynecologist).

Whether you're thinking about getting pregnant or you've already been trying, it's never too soon or too late to evaluate your lifestyle choices. Starting healthy habits or getting rid of the bad ones can improve your overall health. And some lifestyle changes can improve fertility for both you and your partner. For example, quit smoking, reduce alcohol use, eliminate street drugs, practice safe sex, avoid (male) overheating, limit caffeine intake, and exercise regularly.

What is the maximum BMI to be accepted for IVF treatment?

By Marita Espejo Catena M.D., M.Sc., Ph.D. (gynecologist).

Obesity has been shown to decrease the spontaneous fertility of a couple by alteration of the male factor, that is to say, of the seminal quality and also by alteration of the ovarian function.

In addition, gestation rates after assisted reproduction treatments are also reduced when this factor (obesity) is present.

It is probably the female factor that is most intensely affected by a high BMI, since alterations are induced in the ovarian cycle leading to ovulatory dysfunctions and, in addition, a greater number of spontaneous abortions.

Although there is no standardised criterion, it is considered that a BMI in women equal to or greater than 30 may interfere with getting pregnant.

What consequences can anorexia have for a woman seeking pregnancy?

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

The problems of excessive thinness in women can cause alterations in their menstrual cycle. Ovulation can become irregular and even disappear, especially when there is a situation of anorexia nervosa.

On the other hand, the decrease in sex hormones can also affect the development of the endometrium, which makes it difficult to implant the embryo and, therefore, reduces the chances of pregnancy.

What risks do children of obese mothers have?

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

Babies born to obese women are at increased risk for birth defects, such as neural tube defects, cardiovascular abnormalities, and macrosomia (a large baby at birth). They also have an increased risk of complications at birth, perinatal death, and a predisposition to childhood obesity.

Suggested for you

We have mentioned that alterations in weight also lead to an increased risk of obstetric complications during pregnancy. If you want to know more about this topic, we recommend you read the following post: Complications During Pregnancy

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Bellver J, Busso C, Pellicer A, Remohí J, Simón C. Obesity and assisted reproductive technology outcomes. Reprod Biomed Online 2006; 12: 562-568.

ESHRE Capri Workshop Group. Nutrition and reproduction in women. Hum Reprod Update 2006; 12: 193-207

Ferrando M, Bellver J. Impacto de la obesidad sobre la reproducción humana natural y asistida. Rev Esp Obes 2008; 6:302-16.

Nguyen RHN, Wilcox AJ, Skjaerven R, Baird D. Men´s body mass index and infertility. Hum Reprod 2007; 22: 2488-2493.

FAQs from users: 'How does one's lifestyle affect fertility?', 'What is the maximum BMI to be accepted for IVF treatment?', 'What consequences can anorexia have for a woman seeking pregnancy?' and 'What risks do children of obese mothers have?'.

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Authors and contributors

 Marita Espejo Catena
Marita Espejo Catena
M.D., M.Sc., Ph.D.
Graduated in Medicine and Surgery from the University of Valencia in 1992. Specialist in Gynaecology and Obstetrics. Doctor in Medicine from the University of Valencia in 2000. Master in Assisted Human Reproduction by the Rey Juan Carlos University and IVI in 2008. Currently, she is the director of Instituto FIVIR. More information about Marita Espejo Catena
License: 464616497
 Victoria Moliner
Victoria Moliner
BSc, MSc
Degree in Biochemistry and Biomedical Sciences from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Presently, she works as a Research Biologist. More information about Victoria Moliner
 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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