Are You Wondering About Weight? How BMI Impacts Fertility

Being overweight or underweight can affect our health in lasting ways, from heart health to bone health. But weight can influence your fertility, too. If you have struggled with your weight and are having difficulty conceiving, you are not alone. In fact, almost half of the women of reproductive age in the U.S. are obese, and weighing above or below a healthy BMI accounts for up to 12% of infertility cases. (1)

BMI, or body mass index, is a metric that categorizes your weight range based on the relationship between your height and your weight. A BMI between 18.5-24.9 is considered healthy, while a BMI below 18.5 is underweight. A BMI between 25-29.9 is considered overweight, and a BMI above 30 is defined as obese. Of course, what it means to have a “healthy” BMI can vary from person to person. A professional athlete, for instance, may have a BMI falling in the overweight or obese category due to muscle mass -- despite being in peak condition.

Normally, your brain releases hormones that send signals to the ovaries. These signals lead to the growth and release of eggs. But for obese individuals, a confluence of hormone imbalances can interfere with this system and cause ovarian dysfunction and anovulation, which means that the ovaries are unable to release the egg. (2) There are a few theories behind why this happens. For one, fat cells in the body produce a hormone called leptin. If there is too much leptin, it can hinder the ovary’s ability to produce hormones and the process of ovulation. (3) At the same time, obesity can result in insulin resistance, which results in too much insulin traveling throughout your bloodstream. Excess insulin suppresses a protein called sex hormone-binding globulin (SHBG), which subsequently allows for an overabundance of androgens (a group of hormones that includes testosterone). This similarly impairs ovarian function. (4,5) Beyond hormonal imbalances, obesity can also impact the quality of eggs or embryos themselves. (6)

On the other hand, people who are underweight or exercise too much can also encounter fertility difficulties. In these individuals, there is a suppression of gonadotropin-releasing hormone (GnRH), which is the hormone that initiates the cascade of signals that normally tell your ovaries what to do during the reproductive cycle. This lack of GnRH results in estrogen deficiency and irregular periods.

The last piece of this puzzle is how your partner’s weight affects sperm production and function. Some studies have indicated that being either obese or underweight can be accompanied by a lower sperm count and decreased sperm motility, while other studies have suggested otherwise. (7,8) And as with ovulation, obesity can also alter hormone levels governing the reproductive system in these cases. Ultimately, it is not entirely clear how and to what extent obesity impacts sperm function and pregnancy outcomes. (9)

The good news is that there are steps you can take to optimize your weight for a successful pregnancy. As a first step, weight loss can greatly improve ovulatory function and pregnancy rates in obese individuals. (10) While it may take longer for obese individuals to conceive, ovulation induction or IVF could also be worthwhile options to explore along with bariatric surgery. Bariatric surgery has several merits when it comes to fertility, from remedying irregular periods and anovulation to decreasing risks to both you and the baby during pregnancy. (11) It is important to discuss your plans with your doctor and to consider the balance between the benefit of maximizing your health overall and the risk of declining fertility as you get older. Try joining a weight management program alongside other people and doing moderate exercise -- even just a 30 minute walk five times a week can go a long way. (12) Additionally, foods that are rich in folate and omega-3 fatty acids, like kale and salmon, are not only delicious but may help the balance between glucose and insulin and prepare your body for a healthy pregnancy. (13,14,15) Striving towards a healthy weight can not only help you reach your fertility goals but also ensure that you thrive after achieving them.


(1) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(2) Silvestris, E., de Pergola, G., Rosania, R., & Loverro, G. (2018). Obesity as disruptor of the female fertility. Reproductive Biology and Endocrinology, 16(1), 1-13.
(3) Best, D., & Bhattacharya, S. (2015). Obesity and fertility. Hormone molecular biology and clinical investigation, 24(1), 5-10.
(4) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(5) Best, D., & Bhattacharya, S. (2015). Obesity and fertility. Hormone molecular biology and clinical investigation, 24(1), 5-10.
(6) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(7) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(8) Ma, J., Wu, L., Zhou, Y., Zhang, H., Xiong, C., Peng, Z., ... & Liu, Y. (2019). Association between BMI and semen quality: an observational study of 3966 sperm donors. Human Reproduction, 34(1), 155-162.
(9) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(10) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(11) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(12) Practice Committee of the American Society for Reproductive Medicine. (2015). Obesity and reproduction: a committee opinion. Fertility and sterility, 104(5), 1116-1126.
(13) Toledo, E., Lopez-del Burgo, C., Ruiz-Zambrana, A., Donazar, M., Navarro-Blasco, Í., Martínez-González, M. A., & de Irala, J. (2011). Dietary patterns and difficulty conceiving: a nested case–control study. Fertility and sterility, 96(5), 1149-1153.
(14) Vujkovic, M., de Vries, J. H., Lindemans, J., Macklon, N. S., van der Spek, P. J., Steegers, E. A., & Steegers-Theunissen, R. P. (2010). The preconception Mediterranean dietary pattern in couples undergoing in vitro fertilization/intracytoplasmic sperm injection treatment increases the chance of pregnancy. Fertility and sterility, 94(6), 2096-2101.
(15) Intake of protein-rich foods in relation to outcomes of infertility treatment with assisted reproductive technologies.

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