Weight and Fertility

Weight and Fertility: How Your Weight Can Affect Your Ability to Get Pregnant

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Ask any OBGYN or reproductive endocrinologist: weight definitely matters when it comes to fertility. Women who are either overweight or underweight tend to have a more difficult time conceiving. The same is true for men.

Why weight affects your ability to get pregnant

Why, you might wonder, would weight affect fertility? Because a woman's body fat correlates to the hormones her body produces. Simply put, too much fat can cause an overproduction of key reproductive hormones and too little fat can result in the insufficient production of key reproductive hormones.

How do you determine if you're overweight or underweight? One commonly used indicator is the Body Mass Index, or BMI, a ratio of height-to-weight. Enter your vital information in the calculator below to determine your BMI:

Body Mass Index

The recommended 'healthy' BMI range for trying-to-conceive women is between 18.5 and 24.9. A BMI over 25 is considered 'overweight' and anything beyond 30 is considered 'obese'. Anything under 18.5 is considered 'underweight'.

How being overweight can affect your ability to get pregnant

One common issue with being overweight (a BMI of 25 or more) when trying to conceive relates to a potential imbalance of the hormone estrogen. Fat cells actually produce estrogen, and consequently, women with more fat cells tend to have higher levels of estrogen.

Excess estrogen can negatively impact your fertility—essentially acting as a birth control of sorts by preventing adequate ovulation from occurring.

Women experiencing inadequate ovulation are prone to "luteal phase defect". The luteal phase is the time from ovulation to menstruation. Ideally, there are 12 to 14 days between when a woman ovulates and when she menstruates. Women suffering from luteal phase defect, however, have a luteal phase that's too short to sustain pregnancy (less than 10 days).

Polycystic Ovary Syndrome (PCOS) is a common cause of infertility, and is closely linked to weight gain and/or difficulty in losing weight. A diagnosis of PCOS may help you to determine the best path of treatment and assist with any attendant weight issues. Other factors commonly associated with PCOS include:

  • irregular cycles (making it hard to determine your fertile days);
  • ovarian cysts;
  • excess body hair (hirsutism); and
  • heavy, painful periods.
Some women with PCOS may also experience elevated LH (luteinizing hormone) levels, linked to a higher likelihood of miscarriage.

How being underweight can affect your ability to get pregnant

Having a BMI of less than 18.5 may also impact fertility. Being underweight may cause you to experience:

  • anovulation (a lack of ovulation);
  • irregular ovulation; and
  • irregular menstrual cycles.
Being underweight can result in insufficient production of key hormones, leading to ovulation issues which make it difficult to achieve pregnancy. Specifically, insufficient production of GnRH (gonadotrophin releasing hormone) can lead to inadequate development of a uterine lining capable of supporting pregnancy. GnRH also triggers the release of LH (luteinizing hormone) and FSH (follicle-stimulating hormone), necessary in the development of eggs and for ovulation to occur.

Male infertility can also be affected by weight

How does weight affect men's fertility? Low sperm count and sperm motility problems occur with greater prevalence in overweight men due to the excess layers of fat surrounding the testicles. Too much heat around the testicles leads to an increase in temperature which can kill, or negatively affect the development of, sperm.

Being underweight can also affect sperm count, motility, and morphology. For men who want to determine if they're considered in the 'normal' range for weight, the same BMI ranges apply. For optimum fertility, it's best for a man's BMI to be between 18.5 and 24.9 when trying to conceive.

The good news about weight and fertility

Bottom line: it's helpful for both women and men who are overweight or underweight to know exactly how that may be impacting their ability to get pregnant. The good news is that, for many people, working to bring your body weight to within the 'healthy' BMI range often leads the body to restore normal hormonal balance.

As always, consult with your doctor to determine the best plan for your weight loss or gain.

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