Weight as a Cause of Infertility

Weight as a cause of infertility at a glance

  • Excess weight negatively impacts fertility in both men and women, and being underweight can affect fertility in women.
  • Being overweight or obese can result in hormonal problems, higher rates of miscarriage, poor sperm quality, lower pregnancy rates with assisted reproductive techniques and more.
  • The negative effects of being overweight or obese can be reversed through weight management and exercise.
  • CU Advanced Reproductive Medicine has a specialized program to address fertility problems caused by weight issues.

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How does being obese, overweight or underweight affect fertility?

Obesity has increased dramatically across the world and specifically in the United States in recent years. According to the American Society for Reproductive Medicine (ASRM), roughly two-thirds of women and three-fourths of men in the U.S. are considered overweight or obese. Twelve percent of all infertility cases are related to weight issues.

Excess weight not only inhibits natural fertility, but also the success rates of in vitro fertilization (IVF) and other assisted reproductive technologies. Both men and women can have fertility problems caused by weight, and obese couples have a further decrease in fertility.

However, the negative effects of obesity and being overweight on fertility can be reversed by losing weight. The CU ARM fertility specialists are very aware of the challenges in losing weight. From our ongoing, internationally recognized research on the connection between weight and infertility, we recognize weight as the single most important cause of infertility that a man or a woman can change on their own.

We counsel, encourage and guide our overweight patients through the steps of losing weight. For an infertile man or woman concerned about their weight, the first step is to determine a metric to follow.

Body mass index (BMI) is a measurement of body fat based on weight and height for adult men and women.

  • Underweight is a BMI of less than 19.
  • Overweight is a BMI over 25.
  • Obese is a BMI greater than 30.

BMI Calculator

The BMI calculator is a useful tool but does have limits. It may overestimate body fat in those with a muscular build or underestimate body fat in older people.

How is infertility in women connected to being underweight, overweight or obese?

Obese, overweight and underweight women may struggle to conceive. Most often this struggle is the result of ovulation problems.

Women who are overweight or obese take twice as long to conceive compared to women within a healthy BMI range. A study published by National Institutes of Health (NIH) found that obesity and being overweight have increased chances of hypertension, premature labor and gestational diabetes.


Being underweight can cause hormonal problems, specifically the body may stop producing estrogen. These hormonal problems can cause irregular menstrual cycles or stop ovulation entirely. This is particularly true if a woman is underweight from excess exercising or not eating enough.

According to ASRM, it takes women who are underweight four times as long to achieve conception compared to a woman of with a normal BMI. Additionally, babies born to underweight women are at a higher risk for premature birth and low birth weight.


Excess weight can cause an increase in estrogen production by the body, which causes a woman’s body to act as if it were on birth control or were pregnant. This can prevent a woman from ovulation or menstruating.


Obesity has a detrimental effect on a woman’s fertility. Its prevalence in infertile women is high. Obese women have lower rates of embryo implantation. Obese women are also at a higher risk of miscarriage. The risk of miscarriage for women with a normal BMI is 13.3%, whereas obese women are at a 38.1% risk of miscarriage. While there is a link between obesity and miscarriage, there is no consensus about what mechanism causes this.

The research is in

CU Advanced Reproductive Medicine’s own research has found that obesity reduces a woman’s responsiveness to assisted reproductive methods such as hormone therapy.

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Obese women who do have a child have a lower chance of delivering a healthy baby and a greater chance of complications in birth to mother and child. Polycystic ovary syndrome, or PCOS, is a common cause of infertility and can cause obesity.

How does male infertility relate to weight?

Excess weight in men, as with women, can affect the hormones necessary for reproduction. Obesity can cause testosterone production to drop, which lowers a man’s sperm count and cause poor sperm motility.

According to studies published in the NIH, the chances of infertility increase by 10% for every 20 pounds a man is overweight.

Male obesity can affect:

  • Sperm concentration.
  • Total sperm count.
  • Total motile sperm count.
  • Sperm morphology.
  • DNA fragmentation.
  • Reduction in testosterone.
  • Increase in estrogen.

The research is in

CU Advanced Reproductive Medicine’s Dr. Alex Polotsky has a special interest in the relation of weight and fertility. Some of his research examines the connection between male obesity and decreased IVF success rates.

Read more

How to improve fertility through nutrition and weight loss

Through diet and exercise the negative effects of weight can be corrected. Simple lifestyle changes can maximize the chances of conception. Healthy pregnancies begin with healthy parents.

While there is little evidence that a specific type of diet, such as low-fat or vegetarian or ketogenic, has an impact on fertility, a healthy diet is recommended for those trying to conceive. A healthy, balanced diet is composed of fruits, vegetables, lean meats and whole grains.

Regular exercise is not only good for those trying to become pregnant, but is also a healthy habit for anyone to take up. Exercising five time per week, for 45 minutes is considered the standard but may vary for each individual.

Wellness Interdisciplinary Fertility Initiative

CU Advanced Reproductive Medicine and the Anschutz Health and Wellness Center have developed the Wellness Interdisciplinary Fertility Initiative (WIFI), which combines the specialists in fertility and weight management to create a unique weight loss program. Driven by advanced research of the infertility/obesity link, WIFI employs science-based weight loss techniques. Additionally, WIFI provides patients with access to a full range of fertility and health services outside of the program, such as yoga and acupuncture.

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