Weight and Fertility : Are They Related?

Weight and Fertility RelatedWeight and Fertility -  The Relationship

It’s hard to think of two more loaded issues for women then weight and fertility.  We are surrounded by messages about what we should weigh and how our bodies should look. Our fertility is intimately tied with our femininity and sense of self worth. Combine weight and fertility, and you have a powder keg of emotion.

How Weight Effects Fertility

Your weight does effect your fertility in a variety of ways, primarily with respect to your hormone balance.   The amount of body fat you carry effects your estrogen levels. Excess body fat can lead to raised estrogen levels while too little body fat often leads to chronically low estrogen levels.

As you might expect, estrogen  is very important hormone with respect to fertility. A delicate balance of several hormones regulate your menstrual cycle. Normally, your estrogen level is lowest at the beginning of your menstrual cycle, on the first day of your period. When estrogen levels are low and you are menstruating, a signal is sent to your pituitary glad to produce FSH (follicle stimulating hormone).   FSH signals the ovaries to begin maturing eggs for ovulation. As one egg follicle becomes dominant, it starts producing more estrogen which prepares the lining of your uterus to receive a fertilized egg.  Rising estrogen levels also increase the amount and quality of your cervical mucus, which assists sperm in reaching the egg.

Fertility and Obesity

When you are overweight, your estrogen levels may stay too high.  Some excess body fat is metabolically active and causes increased estrogen production. This is in addition to the estrogen normally contributed by your ovaries. The combination of normal levels of estrogen and extra estrogen produced due to excess body fat may lead to constantly elevated estrogen. If your estrogen level never drops enough to signal FSH production, your ovaries will not get the signal to start maturing eggs and you will not ovulate. Obviously if you don’t ovulate, you can’t get pregnant.

Underweight and Infertility

Being  underweight can also suppress ovulation.  Women who are very underweight do not have enough estrogen circulating in their bodies. If your estrogen levels are always very low, you may cease to menstruate all together. This is called amenorrhea. Your menstrual cycle relies on changing hormone levels. If your estrogen level is constantly low, it will not trigger FSH production, thus no eggs will mature and you will not ovulate. If you are not menstruating and you are more then 15% underweight, you are probably not ovulating and you won’t get pregnant.

Weight to Get Pregnant

So what is the “right” weight to get pregnant? Unfortunately there isn’t a magic number, but doctors and nutritionists often use a BMI chart to gauge your overall body fat relative to your weight. Your BMI (Body Mass Index) relates your weight to your height by dividing your weight in pounds (lbs) divided by height in inches (in) squared and multiplied by a conversion factor of 703. Too much math? Try the calculator:

height ft in
weight lb
height cm
weight kg

by calculator.net


Ideally your BMI will be between 20 – 24.  A BMI of 19 or under means you are underweight and may be in danger of amenorrhea.  A BMI of 25 – 29 indicates you are overweight.  If your BMI is 30 or above, you are considered obese.

It’s important to note that the BMI calculation is only rough estimate of your body composition.  An extremely athletic woman that has a lot of muscle mass will likely have a higher BMI that a similar sized woman who is a couch potato, but that does not mean she is less healthy nor less fertile. Use the BMI as a guide, but consult your health care provider for a more thorough evaluation.

Hormone Balance and Fertility

Regardless of your current weight, if you are having normal menstrual cycles, it’s likely that your reproductive hormones are balanced. If you are experiencing irregular (or absent) cycles and you suspect your weight may be an issue, you can ask your doctor to administer blood tests to check your hormones.

It is never advisable to quickly gain or lose weight, especially when you are trying to get pregnant. Strive for a healthy lifestyle and a healthy weight will follow.  If you are concerned about your optimizing your weight for conception, concentrate on eating a well balanced diet based on unprocessed or minimally processed foods. A good rule of thumb is if your great grandmother wouldn’t recognize it as edible, you probably shouldn’t put it in your mouth. Exercise three to five times a week, in a sane manner. A 30 minute walk every day can do wonders for your “bottom” line!

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