How Being Overweight or Underweight Can Affect Fertility

Infertility is a relatively common problem that affects 12-18% of all couples in the United States. Experts attribute one-third of all fertility problems to female factors, one-third to male factors, and one-third to either unknown factors or a combination of male and female factors.

For women, infertility is often linked to hormonal abnormalities leading to ovulation problems and can even be the result of chronic stress and poor dietary habits, especially when associated with being underweight.

Many of the women we see here at Global Fertility & Genetics in Midtown East, New York are surprised to learn that being overweight or underweight can also dramatically influence their ability to become pregnant.

If you’ve been trying unsuccessfully to become pregnant, and you suspect that your body weight may be part of the problem, read on to learn how weight affects fertility, and what you can do about it.   

Body weight and fertility

It may be harder to conceive if you’re significantly overweight or underweight, because both conditions can interfere with normal ovulation, or the monthly release of an egg from one of your ovaries.  

Besides causing anovulation, obesity can also negatively affect quality of eggs and their capability to normally fertilize by semen. As a 2017 study published in Systems Biology in Reproductive Medicine notes, “obesity appears to negatively influence female reproductive function at multiple levels of the hypothalamic-pituitary-ovarian (HPO) axis, and also at the level of embryo development and the endometrium.”

It’s also generally acknowledged that obesity increases the chance of miscarriage.

In women who underwent in-vitro-fertilization (IVF) treatment, being obese lowered their pregnancy success rate: “Obese women who undergo… IVF using autologous oocytes have reduced clinical intrauterine pregnancy rates, increased miscarriage rates, and lower live birth rates compared to their normal-weight peers, after controlling for age.”

Your body fat helps control the release of leptin, a hormone that affects not only appetite and metabolism, but also reproduction. If you don’t consume enough calories, or if you don’t have enough fat stores to support a pregnancy, leptin plays a role in decreasing fertility.

Moreover, a low body weight caused by significant weight loss, “especially when associated with strenuous physical activity and/or heightened cortisol secretion in women, causes hypothalamic dysfunction, with decreased GnRH pulsatility and impaired gonadotropin secretion, subsequently leading to arrested follicle development, oligo-anovulation and prolonged amenorrhea.” Oligo-anovulation is ovulation that occurs less than six times per year, and prolonged amenorrhea refers to extended periods of time with no menstrual period.

The body mass index gauge

Body mass index (BMI) is a quick, easy way to assess your level of body fat and get a better understanding of where you need to be to optimize your chances of conceiving and maintaining a healthy pregnancy.

Your BMI, which is calculated with a simple formula that uses your height and weight, is an indicator of fat levels, but not a direct measure of body fat.

You’re considered underweight if your BMI is less than 18.5, overweight if your BMI is between 25 and 29.9, and obese if you have a BMI of 30 or higher.

By this standard, a woman who is 5’9” tall is considered underweight if she weighs 124 pounds or less, overweight if she weighs more than 169 pounds, and obese if she weighs 203 pounds or more.

Although having a healthy body weight — or a BMI between 18.5 and 24.9 — is ideal for conception and carrying pregnancy, you don’t necessarily need to gain or lose a substantial amount of weight from your baseline to increase your chances of having a baby.

Reaching a healthy body weight

If you’re overweight or obese, simply losing 5-10% of your body weight can be enough to put conception and a healthy pregnancy within reach.

Fortunately, the best strategies for achieving a healthy pre-pregnancy body weight are the same strategies you should use to stay healthy throughout your pregnancy to give your baby a healthy head-start.

Physical activity should be a part of most, if not all, days of the week. That may mean you take a short walk after each meal, swim at the local pool, find a fitness class you’d like to attend, or start a workout program with a trainer. In addition to helping you shed excess pounds, regular exercise will also increase your strength, energy, and stamina — all of which are invaluable during labor and delivery.

Use smaller plates to help reduce portion sizes, and opt for a whole-foods diet that includes plenty of vegetables, fruit, whole grains, nuts and seeds, lean proteins, and healthy fats. Swap sugary drinks (and alcohol) for water, and limit the amount of fast food, processed food, and sugar-rich food you consume.

If you’re underweight, you’ll still want to find time for regular physical activity. You’ll also want to swap out any unhealthy foods and beverages for healthier options.

Most underweight women only need to gain a few pounds to optimize their chances of becoming pregnant. To gain weight in a way that supports optimal health, fill your plate with whole foods, and increase your portions at every meal. Try making healthy fats — including nuts and seeds, olive oil, avocado, and salmon — a part of most meals.

And remember, whether you’re trying to lose weight or gain a few pounds, the team at Global Fertility & Genetics in New York City is always ready to help.