Being Underweight Reduces Your Chances of Pregnancy

The pressure of being thin

Every day society is inundated with photos of thin, beautiful women. The covers of People, US Weekly and In Style Magazine consistently feature women whose average BMI is considered underweight by medical professionals. AND if a celebrity is considered of normal BMI, she is photoshopped to appear thinner than she really is. With a little nip and tuck by the computer “imperfections” are carefully shaded and contoured out. 

Being “too thin” can hurt

The pressure to appear this perfect version of “normal” begins at a young age and stays with women throughout their reproductive years. What if I told you that attempting to achieve that “perfect body”, either by excessive exercise or dieting, could contribute to infertility? What if I told you women are meant to have a certain percentage of overall body fat in order to ovulate and produce quality eggs monthly? 

Much is often said regarding fertility and obesity. My esteemed colleague, Dr. Meghan Oakes wrote a great blog regarding how obesity can contribute to anovulation, infertility and poor outcomes with assisted reproduction. And while this is VERY ACCURATE, the flip side of the coin can also be true: being underweight can contribute to similar difficulties with conception. 

The importance of fat in pregnancy

The body requires a certain amount of energy intake to be coupled with energy utilized —particularly when trying to achieve pregnancy. Much of this is evolutionary. In times of great stress or food scarcity, women’s bodies are designed to prevent pregnancy. Once the stress is resolved and food re-introduced, ovulation occurs again and fertility rates rise. While in the U.S. today in most places we certainly don’t suffer from food scarcity, excessive exercise or dieting can have the same effect.

Excessive weight loss stops ovulation

Oftentimes what we see in our clinic is the phenomenon of “functional hypothalamic amenorrhea” or FHA. Essentially, FHA is when normal ovulation and menstruation stops because the body doesn’t have enough energy – for example, someone may be exercising too much or eating too little. If you aren’t ovulating normally, there is no chance for sperm and egg to unite, fertilization to happen, and a pregnancy to occur. 

The bottom line 

•    To achieve pregnancy, the recommended BMI (body mass index) is recommended to be stable and at least 19. 
•    Heavy exercise, particularly when it interferes with normal cycle regularity, is not recommended when attempting to conceive.
•    If you have a normal BMI (18-25), dieting is not recommended when trying to conceive. 

If you have questions about weight and fertility, give me or my fellow physicians a call at Methodist Reproductive Health Specialists, 402-815-1915.