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How Body Weight & (BMI) Affect a Woman’s Fertility

How Body Weight and Body Mass Index (BMI) Affect a Woman’s Fertility and Ability to Conceive

The impact of BMI & bodyweight on fertility is a hotly contested topic. It can be difficult to figure out how and to what extent bodyweight affects fertility in women based on the survey of current and past medical research. Although there is ample evidence that being overweight has a negative impact on your fertility, it is equally important to note that every woman is different. It is important not to generalize the findings of these studies. There are plenty of examples of women of all sizes getting pregnant, having a non-eventful, normal pregnancy, and giving birth to healthy sons and daughters.  

How does being overweight affect my fertility?
Does your weight, BMI affect your ability to get pregnant

That said, it is now wise to refute science based on a few anecdotes and outliers. Hence, it is important to take a deeper look at what science has to say regarding body weight and its impact on your fertility. Here are some key consolidated findings from a variety of scientific sources –

  • Although the medical fraternity generally agrees that weight impacts your fertility, they also agree that every woman is different. Besides weight, there are many other factors that can have a stronger effect on your fertility than just your weight. 
  • Getting pregnant and having an uneventful pregnancy is contingent on having the right hormonal balance in your body. If you are overweight or underweight, this hormonal balance can be thrown askew and create fertility issues such as irregular periods and anovulatory cycles. 
  • Talking to your OBGYN regarding your ideal BMI is important if you are trying to get pregnant. 
  • That said, always remember that BMI is not a perfect matric, and women deviating from the ‘normal’ BMI get pregnant all the time without any issues. 

First things first: What is Body Mass Index?

BMI (Body Mass Index) uses the ratio of your weight to your height to predict the amount of fat in your body. You can easily calculate your BMI at home by taking your weight in kilograms and dividing it by your height in meters squared. If you prefer not to do the calculations yourself, there are plenty of online tools to do them for you. 

Here are some typical BMI figures for women –

  • Below 19: Underweight
  • Between 19-24: Normal
  • Between 25-29: Overweight
  • Above 30: Obese
Weight, fertility and pregnancy health
Being overweight, obese or underweight can affect a woman’s fertility

It is crucial to understand that BMI is not a perfect matric indicating health by a long shot. One of the issues with BMI measurements is that these measurements can’t distinguish between fat and muscle, and hence if you have high-density muscle mass, you might have a BMI that might indicate that you are overweight. 

Another issue with BMI is that it can’t distinguish between the various types of fats and how they are distributed within your body. For instance, the visceral fat, or the fat that surrounds your organs, is bad fat. Too much visceral fat around your liver, kidneys, or intestines can cause many health problems, including higher susceptibility to developing type II diabetes. BMI within the so-called normal range might also have high visceral fat, and BMI can’t identify such individuals. 

An increasing number of researchers understand the flaws of the BMI system as a standard to predict an individual’s overall health. Having a normal BMI does not necessarily make you healthy, and having a high BMI does not necessarily mean that you are unhealthy. 

How BMI and weight can affect your chance of getting pregnant? 

Several factors contribute to your chances of getting pregnant, including your overall reproductive health and hormone levels. The sperm must fertilize the egg at the ‘right time’ and in the right place within your reproductive tract for you to get pregnant. Hence it is not wise to think that BMI alone has an impact on your fertility. Women with all kinds of BMI figures can and are getting pregnant all the time. 

One of the strongest links between being overweight and fertility comes in the form of the hormone estrogen. The amount of estrogen your body produces has a profound impact on your chances of getting pregnant. Estrogens are mainly produced in the ovaries, but a small amount is also synthesized by the fat cells and the adrenal glands’ cells. Consequently, if you have a higher body fat percentage or a higher BMI, your body has a higher number of fat cells, and there is a higher amount of estrogen being produced in your body. 

Estrogen is also responsible for the thickening of the uterine lining called the endometrium. Hence, if you have a higher estrogen level due to being produced by more fat cells, you might have a thicker uterine lining, and when it sheds, you might have heavy periods. 

Too much estrogen in your body is not a good thing for your reproductive health. It might lead to irregular periods and can even prevent ovulation. A higher estrogen can also affect how your body processes glucose. It is also documented that higher estrogen concentration might lead to polycystic ovarian syndrome (PCOS). Having a higher fat percentage in your body might also negatively impact the success of fertility treatments, including IVF & ICSI

So, does it mean that being underweight is better than being overweight? Not. Having a low BMI implies that your body does not have enough fat, and its energy demands can’t be met. The production of estrogen is also affected by it, and you can experience irregular periods or completely stop having periods altogether. As you can imagine, if you have irregular cycles, you might have difficulties in conceiving. If this happens, all the processes that are not essential for your survival would be negatively impacted, slowed down, or completely shut off. 

Polycystic Ovary Syndrome, Body Mass Index (BMI)
Polycystic Ovary Syndrome, Body Mass Index (BMI) and Fertility Outcomes courtesy of couri center

Certain health conditions can also affect BMI.

Being overweight is not always simply because you are consuming more than what your body needs. There are legitimate medical conditions such as hypothyroidism that cause you to gain weight. 

Another common reason for gaining weight is PCOS. It is a condition in which your ovaries develop cysts. Women with PCOS generally have issues keeping their weight down despite trying many things. If you have PCOS, the level of a hormone called anti-mullerian hormone (AMH) might be elevated in your bloodstream. Some women with PCOS also have elevated levels of androgens (male sex hormones). Although androgens are present in all women, having PCOS might increase their concentration. 

Another common problem with PCOS is the development of what is called insulin resistance. Your body’s cells become resistant to insulin if you have PCOS, making it difficult for them to absorb glucose from the blood, resulting in chronically elevated blood glucose levels. According to some studies, 80% of women with PCOS have a higher BMI because it is a disease in which your body’s metabolism is severely affected. 

Anorexia and other eating disorders can also lead to a host of health issues resulting from malnourishment. Anorexic women have a lower concentration of estrogen in their bodies, leading to irregularities in their periods and anovulatory cycles. 

What to do if your BMI isn’t within the ‘normal’ range? 

Having your BMI within the so-called normal range (between 18-25) is not a prerequisite to get pregnant. However, if you have a BMI that classifies you as being ‘overweight,’ losing a few kilos might positively impact your fertility. Several meta-analytical studies have found out that losing weight has, in general, a positive impact on your fertility. 

That said, losing weight is not the only answer. It is difficult to comment on the effectiveness of weight loss on fertility without a proper evaluation. Losing too much weight might do more harm than good to your chances of conceiving. Losing the subcutaneous fat will not help; the visceral fat needs to go if you want to get on top of your metabolic fertility issues. 

Both being overweight and underweight is not good for your fertility and overall reproductive health. But the good news is that you can take control of your health with steps in the right direction. Talk to your healthcare provider about any questions you might have. 

How to track ovulation to get pregnant

It is always a good idea to track your ovulation if you are trying to conceive. With Fertility2Family’s cheap and easy ovulation prediction kit, you can do just that from the comfort of your home. Using ovualtion tests will allow you to gain insights into your cycle and will enable you to learn when you ovulate and the best time to have sex to get pregnant.