BMI: The Silent Fertility Issue

image of foot on scale

Body Mass Index (BMI) is not the first thing people think about when planning family building. It is, however, an important factor with many implications. BMI is one of the tools that fertility specialists use early in the diagnosis process. The ratio of weight and height is used to categorize a patient’s BMI and how it impacts one’s fertility.

In order to understand how BMI affects fertility, it is important to first understand BMI generally, and how physicians use it as a scale of health:

  • Underweight individuals have a BMI of less than 18.5
  • Normal weight individuals have a BMI that falls between 18.5 and 24.9
  • Overweight individuals have a BMI that falls between 25 and 29.9
  • Individuals with obesity have a BMI of 30 or greater

Knowing an individual’s BMI allows fertility specialists to understand their overall risk in pregnancy. It also may help predict what sort of response to treatment a patient will have and therefore, an appropriate choice of fertility treatment protocol and medication dosage.

Effects of BMI on Female Fertility

Abnormal cycles
Ovulation is the ability to release an egg every month. The average menstrual cycle length is 28 days but can range from 21 to 35 days. Ovulation can be affected by being both underweight and overweight. So, if cycles are falling outside of that range of days, that could signal ovulatory dysfunction, meaning the hormonal signals that are sent from the brain to the ovaries are out of balance and weight can impact those hormonal signals from the brain.

  • Higher estrogen levels: With increased BMI, women can have higher estrogen levels. This comes from the fact that adipose tissue, or fat tissue, can make estrogen itself. Higher estrogen levels can lead to ovulatory dysfunction.
  • Decrease in Gonadotropin-Releasing Hormone (GnRH): In females with a low BMI, the brain may not produce enough GnRH–the hormone that tells the pituitary gland to release FSH (follicle stimulating hormone) and LH (luteinizing hormone). Without these hormones, ovarian follicles cannot grow and therefore ovulation cannot occur which is imperative to conception. The low levels can lead to no ovulation or irregular or sporadic ovulation.

High-risk pregnancy
BMI can also impact if someone has a high-risk pregnancy or not and is prevalent in both underweight and overweight individuals.

  • Underweight individuals: They are at a higher risk for having babies that are underweight and they’re also at risk for preterm labor and preterm birth.
  • Overweight individuals: Are at an increased risk for miscarriage, both first-trimester miscarriage and fetal demise which is the passing of the infant after 20 weeks-gestation. With a higher BMI, there is also a higher risk for high blood pressure during pregnancy. This condition can lead to pre-eclampsia — high blood pressure and pregnancy accompanied by protein in the urine. Pre-eclampsia can lead to serious complications during pregnancy and delivery. High BMI is also linked to an increased risk for diabetes in pregnancy (gestational diabetes), as well as birth defects; in particular, cardiac defects and neural tube defects. There is also an increased risk of preterm birth.

Safety of IVF
BMI can also influence clearance for anesthesia since overweight individuals are at higher risk while under anesthesia, which is commonplace during fertility treatments.  For this reason, as well as pregnancy risks, many fertility clinics have BMI-cut offs for treatment.

Effects of BMI on Male Fertility

Hormone imbalance
For men, having excess weight can lead to hormone imbalances as well. Obesity elevates body temperatures, specifically around the scrotum. They can be experiencing lower testosterone production and higher estrogen production with obesity, in particular with a BMI greater than 30.

Abnormal sperm production
Abnormal hormones can, in turn, lead to abnormal sperm production. When doing a semen analysis, physicians are looking at sperm parameters: the total count of the sperm, the shape of the sperm, and how they are swimming. Are the sperm moving forward or standing in place? Sperm movements are predictive of the ability to conceive. Excess body weight can lead to excess cortisol levels, hormonal disturbances in the male partner, and in turn, abnormally shaped sperm. Abnormally shaped sperm are associated with irregularities such as low sperm count or motility, which often results in poor fertilization rates.

Tips and Treatment

Find a physician you trust

Gaining or losing weight is no small feat. The journey on the path to parenthood is a strain enough and having to transform your body can be a lot to handle. Because of this, it is crucial to find the provider that is right for you, one who will go over dietary plans, be available to support you along the way, and provide resources that make your journey easier. It’s especially important to keep track of your mental health while undergoing fertility treatment and to make sure that you are receiving the support you need to maintain balance in your life.

Incorporate a healthy diet and mind

To help with a healthy body is also a healthy mind, which may mean reducing stress levels. Some effective and healthy tools for stress management include yoga, acupuncture, meditation, regular exercise, a healthy diet, and getting adequate sleep. A conversation with your healthcare provider, a friend, a therapist, or a peer who has been through fertility treatment themselves can provide some insight as to what might work for you.

Weight loss and weight gain are the two broad umbrella solutions for those who may be facing infertility. Although changing your weight may be best in these scenarios, it’s important to take it at your own pace. Find a diet that will work in the long term. For example, extreme calorie counting, or a macro-based diet can be hard to follow and continue. Studies have shown that the most important foods for optimal female and male fertility include a wide variety of fruits, vegetables, and whole grains. The closest to an ideal “fertility diet” is the Mediterranean Diet. It’s important to speak to your physician to find the right plan that will work for your body.

Exercise based on your BMI

For those with a normal BMI, 30 minutes of moderate exercise four to seven days per week can help to maintain a healthy weight and reduce stress. On the other hand, for individuals who are overweight or obese, 30-60 minutes of vigorous exercise five to seven days per week is recommended.

For men, evidence has been shown that as little as being physical and active can differentiate someone with low sperm quality from someone with high sperm quality. Weight resistance or cardiovascular exercises are most recommended for maintaining a healthy lifestyle and boosting testosterone levels. It is important to keep exercise at a moderate level and not to overdo it.

The benefits of changing one’s weight

If a patient has a high BMI, some degree of weight loss will help improve fertility, and for those pursuing fertility treatment, it helps with response to medication. During IVF, weight loss can lead to safer fertility treatment protocols, for example during the egg retrieval process. Weight loss can help with optimum pregnancy outcomes and maximize treatment efficiency. Gaining weight for those that are underweight can help restore normal menstrual cycles and help with natural predictability or the ability to conceive on their own as well.

There are also other conditions that can impact one’s weight such as Polycystic Ovarian Syndrome (PCOS) and endometriosis. These conditions may make it harder to lose weight and reach your optimal BMI.

REVIEWED BY: Dr. Desiree McCarthy-Keith, Shady Grove Fertility in Atlanta
Dr. McCarthy-Keith earned her medical degree from the University of North Carolina at Chapel Hill and also a Master of Public Health in maternal and child health from the University of North Carolina. She completed her Obstetrics and Gynecology residency training at Duke University Medical Center and a fellowship in Reproductive Endocrinology and Infertility at the National Institutes of Health in Bethesda, Maryland. During her fellowship, Dr. McCarthy-Keith’s research focused on the molecular mechanisms of uterine fibroid regulation and reproductive health disparities. She has special interests in male and female infertility, polycystic ovary syndrome, uterine fibroids, and in vitro fertilization. She has authored several peer-reviewed publications on reproductive and infertility topics and has presented her research nationally.
Prior to joining SGF Atlanta, Dr. McCarthy-Keith practiced general obstetrics and gynecology in Virginia and South Carolina. While in Maryland, she treated patients with reproductive endocrine and fertility disorders at the National Institutes of Health and Walter Reed Army Medical Center. Dr. McCarthy-Keith was a Lieutenant Commander in the United States Public Health Service Commissioned Corps and held the position of Assistant Professor of Obstetrics and Gynecology at the Uniformed Services University of the Health Sciences. Dr. McCarthy-Keith is passionate about her vegan way of life. She shares her enthusiasm for plant-based nutrition with everyone she meets and she encourages her patients to incorporate healthy diet into their fertility lifestyle. A native of North Carolina, Dr. McCarthy-Keith is the proud mother of two energetic sons. She spends her free time in Atlanta visiting the zoo, strolling the botanical gardens, and cheering on the Braves.