Weight and Fertility

Did you know weight can affect one’s fertility and one’s chances of getting pregnant?

In terms of a woman, we’re talking about the extremes of weight; whether someone is underweight, or whether someone is overweight, and especially, if someone is in what we call the obesity range.



Women Who are Underweight

This may come as a surprise to some people, but someone who’s underweight, especially someone whose body mass index (B.M.I.) is under 17, may not ovulate.

[ms_popover title=”B.M.I.” triggering_text=”Click here to learn more about Body Mass Index” trigger=”click” placement=”top” class=”” id=””]Body mass index is a ratio calculated based on your height and your weight. This is an international standardized method for determining someone’s weight ratio and if someone’s body mass index is under a threshold number. In our case, we’re especially concerned about 17 to 18 BMI[/ms_popover]


Who are the people who tend to be in a low BMI range? 

These tend to be people who may have an eating disorder or body dysmorphic image disorder. Some of the common disorders related to body dysmorphic states would be anorexia nervosa, bulimia, (someone who does what we call the binge and purge); they eat a lot, and then they purge themselves by vomiting or using excessive laxatives to purge themselves.

Other cases where BMI may be under 17, might be someone who’s had a really significant or excess weight loss in the context of an illness. Some patients who have overactive thyroid or hyperthyroidism, (Graves disease being the most common form of hyperthyroidism) also can develop excess weight loss that can lead to this state.

The reason why these women don’t ovulate is usually due to the fact that in these different body states, the brain gets a message that says, essentially, “We are not healthy enough to be pregnant.” So the pituitary gland, which is this really small gland in the brain that controls a lot of your hormonal functions in your body and especially drives your reproductive messaging will shut down. That is a case we call hypo pituitary or hypo pituitary hypergonadism.

In hypo pituitary cases the brain– specifically the pituitary gland–shuts down the messaging that it usually sends to the ovaries. The ovaries, in turn, stop ovulating. These patients become “infertile” because they’re not releasing eggs.

There’s a host of other factors that can play a role in that weight loss. When someone comes in to see me as a fertility specialist, one of the things I pay close attention to is whether they’re underweight, and nutritionally, whether we need to figure out how we change the messaging to the body. For some people, once they’ve become hypo pituitary hypogonadism, the body doesn’t spontaneously ovulate even after they’ve regained some weight or some body fat.

12% body fat or more is about the ideal range to help promote ovulation.

These patients may still need medication to help them release the egg or to ovulate but the first step is to assess why they’re underweight and make sure there’s not a medical condition underlying the cause of the low weight that we need to address.

Ultimately, we want the patient to bring their weight up even if we help them ovulate with medications, so they are nutritionally healthy enough to carry the pregnancy. That’s why weight is so important. It’s about the ability to carry a pregnancy.


Women Who Are Overweight

On the other end of the spectrum, are women who are overweight, being in a BMI category above an index of 25. Again, the normal range for body mass index is 18 to 25.

Anyone over 25 is considered to be overweight based on the BMI criteria. Anyone whose body mass index is over 30 is considered to be obese. Then there are different classes of obesity, with Class 1 being a BMI of 30 to 34.9. 34.99, actually. Class 2 obesity being body mass index of 35 to 39.99. And then Class 3 obesity being a body mass index greater than 40.

Why do we need categories or classes of obesity? Well, they help us determine the interventions that we need for a patient. It also helps us figure out how much weight we may need to counsel them on losing, and what sort of weight loss interventions we can pursue. For example, a woman whose BMI is well over 40, meaning she’s well into Class 3 obesity, may need some more aggressive options for helping her lose weight.

The first step is to figure out why this patient has the weight? Is there an underlying condition that we need to diagnose?

Just as someone could have an overactive thyroid that causes them to be underweight e.g., hyperthyroidism or Grave’s disease, some patients can have an underactive thyroid, causing them to develop hypothyroidism. Hypothyroidism can be due to a goiter. It can be due to Hashimoto’s thyroiditis. It can be due to a history of thyroid cancer that was treated, and now they’re underactive in their thyroid function. We look at all of these possibilities.

There are other things that can cause weight gain in the context of infertility that can further contribute to the issue. Polycystic ovary syndrome or P.C.O.S. is fairly common. It’s the leading cause of anovulation–not releasing an egg in patients who have infertility. So we also screen and determine whether or not P.C.O.S. is playing a role. If it is, then we treat the underlying P.C.O.S. as part of our treatment for their weight gain, which in turn can cause them to ovulate spontaneously.

These are just two examples of how a woman’s weight can actually be due to an underlying issue that leads to her not ovulating. It’s important to remember that.

Both being overweight or underweight can result in a clinical case where the patient doesn’t release an egg. That’s where coming to a specialist such as myself, a reproductive endocrinologist and infertility specialist, is helpful. We are trained to identify these different scenarios and to really tease apart the cause, and the appropriate treatment for patients.

I could easily have two patients sitting before me, both of whom are overweight, but the reason for their being overweight is different, so the way I treat them would be different.

I really like to emphasize this, because we’re now in the age of technology, with easy access to information and a lot of patients go online and they look stuff up, or they talk to a friend and their friend says, “Well, this thing worked for me…” Then the other person, who is obviously trying to get pregnant and willing to try most things, goes ahead and tries what they’ve read online, or what a friend or family member has counseled them to do. Then they don’t see any results because they’re not addressing the underlying issue specific to their case.


Other Causes of Weight Gain

Some other causes of weight gain include:

  • diabetes (and weight increasing medications),
  • genetic hormonal imbalances
  • medical treatment for things like autoimmune diseases

With autoimmune diseases, we can see weight gain in patients who perhaps were on a high dose of longer-term steroids for suppression of an illness such as lupus or some other autoimmune condition. This may, in turn, have affected their weight, and thus their ability to ovulate. So again, seeing a reproductive endocrinologist really helps, as we can figure these things out and treat appropriately.

How do we treat once we figure out that there’s a weight issue contributing to someone’s infertility?

Sometimes it can be as simple as helping her get started on a lifestyle change where she’s more active, perhaps lifting more weights and/or getting a nutritionist on board. Multidisciplinary involvement with other health care professionals such as nutritionists, personal trainers, physical therapists is one strategy. If our patient has any issues with mobility due to her weight ( i.e., joint problems or knee problems) we may have to get a physical therapist involved. Sometimes, patients need more major interventions like surgery and in that case, we treat that too.


A Note on Male Weight and Infertility

Believe it or not, a man’s weight can also affect his fertility. What we know now, is that there is good data to support that a man who’s overweight can have issues with his sperm count and quality. Whether it’s related solely to him being overweight is still up for debate. Sometimes, it’s more likely due to comorbid conditions or diseases that are usually affecting him as a result of weight such as type 2 diabetes. Guys with sleep apnea and other problems sleeping, (and thus oxygenating well), may also have reduced sperm quality.

In some men who are overweight, it may be because they’re on other medications. The medications may be suppressing their testicular function. Not only can they have low testosterone, they can have low sperm production–hypo pituitary hypogonadism–much like we described with women.

This is why when a female patient comes to us for evaluation, we ask all these questions about the male too, to assess whether he may have a weight-related issue that’s also affecting his fertility.


Some Closing Thoughts

Each patient is different and treatment is completely individual. I really stress this point, because infertility and how it manifests in a patient varies depending on all the other factors relating to the patient; be it her underlying health, whether she has any underlying medical conditions, diagnosed or not yet diagnosed. It depends on what her diet is, what she’s exposed to in her physical environment–what she eats and where she works. Is she exposed to radiation? What medications is she on? What are here underlying genetics? For all women, genetics play a role. These are all things that we take into consideration holistically for each patient, on a case by case basis.

I’m not suggesting that if we solve someone’s weight issue, they’re now fertile. Although, for some patients, that’s what it takes. For some patients, 5% to 10% weight loss is sufficient to get them ovulating. If anovulation–not ovulating regularly–was the sole reason for their infertility, if we can get them ovulating regularly, we may be able to solve that issue.


The truth is your body really is a system of messages. Our endocrine system is really important when it comes to determining our hormonal functions, and thus our reproduction, our metabolism. Our success at conceiving and carrying a pregnancy is in part dependent on our endocrine system and how well it functions.


A patient will say, “I used to ovulate regularly and then I stopped ovulating regularly.” At that point, I usually ask a very straightforward question, “Oh, did you gain some weight in that time?” And she’ll say, “Yeah, I gained weight.”

A period of weight gain may be enough to change the set point for your brain and your pituitary gland to stop you from ovulating. Likewise, you could have lost so much weight that your brain’s set point for when it ovulates would have changed. In either case, your brain tells your ovaries, “Let’s not ovulate. Something is going on. I’m not sure what’s happening. She’s losing (or gaining) a lot of weight. Let’s wait.”

Ultimately, I like to tell patients the good news about weight and it’s effect on fertility… 

Weight is a modifiable factor. It’s something that we can change–something that we can work on together to help get the patient to a weight that’s more conducive to their goal of conceiving and sustaining a healthy pregnancy.



Q & A

Questions & Answers with Dr. Cindy

Q: “I am supposed to get I.V.F., but I was told that I need to lose weight. Why is that?”

A: Many practices have weight thresholds for a patient being able to proceed with doing in vitro fertilization. In vitro fertilization is a process whereby we give the patient a fairly high dose of hormonal medications to get eggs from her ovaries, and then we get sperm from her partner.

The reason for requiring weight loss is varied. For some clinics, they have a weight threshold based on their requirement for the anesthesiologist. For some anesthesiologists, in order to do a procedure outside of the hospital, you need to be under a certain body mass index.

For some clinics, it’s also based on the fact that women who are at the higher B.M.I. levels tend to also have poor outcomes with in vitro fertilization, meaning their chances of success are lower. Of course, it’s not just their weight that affects those chances; it’s varied, based on the number of eggs you have, your age, et cetera. Higher B.M.I. is certainly a factor that we’ve found to be associated with diminished success rates in patients undergoing I.V.F., and so it is not uncommon for a physician to counsel a patient that to lose weight to get under a certain threshold, so we can have better outcomes. I.V.F. is also a big financial investment, as well as an emotional investment. Your doctor is really trying to improve your chances as you embark on this huge investment in your life.

Other things to keep in mind with I.V.F., are the medications. Some of the medications that you’re taking are injectables that ideally go into your body’s fat deposits. So body mass index, your body fat percentage might change how much of the medicines you need; it might affect your dosing, which in turn can, again, change your costs for your procedure and how much medication you need.

Q: “Why does my male partner need to lose weight? He’s had children before. His weight wasn’t an issue then.”

A: For men who have always been on the overweight side, as you age, your body may not adjust for certain issues the same way it did as when you were younger. You may now have new weight-related illnesses that have developed as you’ve moved on.

For example, perhaps you’ve now developed type 2 diabetes when you didn’t have it before, but you’re at the same weight, that could be affecting things. Certainly, there will be patients who’ve had children, have a great sperm count, and are overweight. They may even be in one of those classes of obesity and yet, their fertility–sperm count, and quality is fine.

Q: “Why does weight matter for women? Is that really true? Because yes, I know women who are overweight who’ve had children.”

A: The simple answer to that is you are correct. There are women who are overweight and spontaneously conceive and get pregnant. That, however, is not the majority of women who are in the higher categories of being overweight.

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