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American Family Children's Hospital

Understanding Body Weight and Fertility

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Generations Fertility Care

2365 Deming Way

Middleton, WI 53562

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(608) 824-6160

(888) 474-3933

Weight is never an easy subject to talk about - not only does it affect how you feel about your appearance, but it can also have potentially adverse effects on your health. While you may know that being under or overweight can lead to issues with your cardiovascular or immune systems, you may not realize that it can also affect your fertility. It’s important to understand how weight affects your fertility to improve your chances of conception.


What is Body Mass Index?


When you speak with a fertility specialist about weight, he or she will refer to your body mass index or BMI. This is a calculation that divides your weight by your height. BMI is an indicator of how much body fat you possess. Generations Fertility Care follows these BMI guidelines:

  • Underweight: Less than 18
  • Normal: Between 18 and 25
  • Overweight: 30 and above

While being under or overweight does not necessarily mean you will have difficulty conceiving, your weight can have a direct effect on your fertility.


How Being Underweight Affects Fertility


Women who have a BMI less than 18 may have trouble conceiving due to the following:

  • A lack of necessary nutrients essential to egg development can decrease hormones in the ovaries.
  • This lack of nutrients can also create a hormonal imbalance, which can cause hypothalamic amenorrhea. This is a condition in which ovulation and menstruation do not occur. Without ovulation, the ovaries do not release eggs, which means conception is not possible.

If you are underweight and experiencing infertility, it's important to be evaluated by a fertility specialist to determine an appropriate path forward. Possible recommendations may include:

  • Medical evaluation. For some women who are underweight, there may be an underlying medical cause. If this is the case, it’s important to work with your primary care physician to treat the underlying cause before trying to conceive.
  • Health and wellness care. We recommend working with a dietician and your primary care physician to receive a personalized care plan for healthy diet and exercise. Additionally, your specialist may recommend speaking with a psychologist or joining a support group to help you on your fertility journey.
  • Medically induced ovulation. In certain cases, a woman may be naturally underweight without an underlying condition, or she may be unable to gain enough weight to reach a normal BMI. A fertility specialist can use ovulation induction medications to stimulate the hormones that cause ovulation to occur.

How Being Overweight Affects Fertility


If you are overweight and having difficulty becoming pregnant, a lack of ovulation and menstruation may be the reason. While this is the same issue if you are underweight, the cause is different. If you are overweight, extra fat increases insulin levels, which causes your ovaries to produce too much testosterone. Too much testosterone leads your ovaries to stop releasing eggs.


Additionally, being overweight can affect your response to fertility treatment, including in vitro fertilization (IVF). You may have a lower response to medication and difficulties with embryo transfer, leading to lower IVF success rates.


Thus, it's important to speak with a fertility specialist if you are concerned that being overweight is affecting your ability to conceive. He or she may recommend:

  • Medical evaluation. Being overweight is not always due to diet and lack of exercise. It's important to be evaluated for underlying conditions that may affect your weight, such as polycystic ovarian syndrome (PCOS). Your doctor can then manage and treat your condition before you try to conceive.
  • Health and wellness care. Reducing your BMI through healthy diet and exercise can increase your chances of becoming pregnant. Your primary care physician and a dietician can help you create a plan to lose weight in a healthy manner. To support you with the emotional side of this journey, your physician may recommend seeing a psychologist or joining a support group.

The Effects of Weight on Male Fertility


Though it only takes one sperm to fertilize an egg, a low sperm count or sperm that doesn’t move very well (known as motility) significantly reduces your chances of conception. Being over or underweight can cause both of these sperm function issues.


By employing a healthy diet and moderate exercise, your sperm count may increase and motility may improve. As with women, though, it’s important to be evaluated by a specialist if weight is the suspected cause of infertility to determine if there’s an underlying medical cause that needs to be treated first.


Learn More


If you have questions about weight and fertility or are ready to schedule an initial consultation with one of our fertility specialists, please call (608) 824-6160 or complete our online form.