Ideal Body Weight & Fertility

I wanted to address this topic as one of my first because it might take all year to get it right.  Achieving a healthy weight is an important indicator of overall health, fertility, and baby’s health during pregnancy (and afterwards… it’s just an overall big deal).

What is ideal body weight? It isn’t necessarily that magic number in your head the mysteriously equates to looking like a supermodel and having a perfect flat belly.  There really is no perfect number.  Ideal body weight is just meant to represent a healthy range where you reduce your disease risk and improve health scores (including fertility).  I do not believe that this number is the same for everyone or that there is a perfect formula to tell you exactly where you should be; there is a huge variety of healthy body shapes and composition.  The bottom line (for our purposes) is that major imbalances in weight (whether too high or too low) will affect your fertility.

How do you gage where you are at?  There are several tools that you can use to assess ideal body weight.  The two easiest and most well researched are Body Mass Index (BMI) and waist circumference. Here is how you calculate them.

For BMI, divide your weight in kilograms by your height in meters squared (kg/m2). For example, if I am 5’5” (1.651m) tall and weigh 140lbs (63.502kg), then my calculation would be:

BMI = 63.5/(1.652) = 63.5/2.73 = 23.3

*Note: If the math intimidates you, there are several simple BMI calculators online where you can just plug in your height and weight.  Just Google ‘BMI calculator’.

A BMI of 23.3 would put me in the “Normal Weight” category, which means I am in the group with the lowest risk of disease (purely based on statistical averages).  In women, a BMI of over 27 or under 17 is associated with decreased fertility.  In some places, having a high BMI will automatically exclude you from any publically funded fertility treatments.

<18.5 Underweight
18.5-24.9 Normal Weight
25-29.9 Overweight
>30 Obese

*Numbers acquired from Health Canada.

The criticism for BMI is that it does not take into consideration body composition.  This is true.  A very large muscular person would have a high BMI, even if they had a very low body fat percentage.  My assumption is that you know if you are one of those exceptions.  If you are a normal gal like me, these can still be meaningful enough numbers to let you know if you are on the right track or if you have more work to do.

Although being overweight is by far the more common dilemma, being underweight can be just as much of a problem, especially when it comes to fertility.  If your body does not have enough energy and nutrients to support your own healthy physiology, it is not going to be able to support new life inside of you either.  If you struggle with any eating disorder (anorexia, bulimia) or have amenorrhea (no menstrual cycle), resolving it absolutely needs to be your top priority if you ever want to have a family.

For waist circumference, the key to accuracy is consistency.  The measurement should be taken with a soft measuring tape horizontal (level) on both iliac crests (the top of your hip bones).   Your final measurement should be at the end of a normal expiration.

* is a useful tool if you want more guidelines for self-measurement, a video demonstration, or a measurement log form. 

Waist circumference has different ranges for men and for women and for different ethnic groups.  For Caucasian (or Europid) women, waist circumference should be less than 80 cm.

I like waist circumference as an anthropometric measurement because it is an indicator of central adiposity.  Central adiposity has a very high correlation to metabolic disease, which makes sense considering the chub evident around the midline from the outside is a likely indicator of the fat encircling your organs on the inside (visceral adiposity).  It is becoming more prominently used than waist-to-hip ratios.

What do you do with your scores?  For some people, numbers seem meaningless or intimidating, while for others find them very helpful.  Regardless of your relationship with numbers, the purpose of us going through these exercises was to help you develop on honest foundation for your yearlong fertility health journey. If you are already within the healthy ranges, awesome! Maintain the good work.  Maybe you are close to where you want to be, but need to pick up that last bit of slack. Or maybe you have a ways to go, and these honest numbers are forcing you to recon with that.  Either way, it’s time to develop a plan.  A real, permanent-change type of plan.  Not an “Oh crap! I need to lose 50lbs stat! Time for another crash diet and starvation” type of plan.  We are talking about real health here.  Start a fitness routine. Make a dog-walking schedule.  Prepare healthy lunches for work.  Make a REAL plan. This blog will hopefully help you along the way, but at the very basic level: eat healthy food and move your body every day. The good news is that research has shown that improving these measures restores normal physiology and fertility in the majority of cases.

The last thing I wanted to mention is body image.  This is a huge topic, but I only want poke your thinking wheel.  Being happy with the skin you’re in is an incredible feat.  It will lower your stress levels and improve your health scores.  So be realistic and love who you are during every step of the journey as you strive to continually improve and develop as a woman.

This stuff isn’t just important for women!  Excess weight and high BMI in men has been linked to lower testosterone levels, higher estradiol levels, poor semen quality, and infertility.  We’ll talk more about them later.

How does obesity effect male fertility?


More than anything I just want you to be honest and happy with yourself.  This blog post is a little more boring than most, but it is meant to help you build an honest starting point.  Now let’s get to work.



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