The effect of weight on fertility

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Being overweight can have a significant negative affect on fertility and pregnancy.  Fortunately, losing weight can help improve the chance of conception and minimise the risks of pregnancy complications. Over 20% of the Australian population are obese and this figure is rising year by year.  Apart from difficulties in conceiving, obesity increases the risk of miscarriage, birth defects, obstetric complications and still birth. Unfortunately, these risks are often overlooked by patients who are desperate to have a child.  

Obesity in women has a profound affect on fertility due mainly to anovulation, but also other more subtle metabolic effects due to elevated insulin.  Women with a BMI of 25-30 kg/m2 are 50% more likely to have anovulatory infertilty than in women with a normal BMI. This rises to 300% in women with a BMI over 30 kg/m2.  Unfortunately, IVF success rates may be reduced by as much as 25% in obese patients and 50% in very obese patients. You can check your BMI here on our calculator.

And its not just the weight of the female partner that is important  – obesity in men also has an effect on fertility. Obesity can lower sperm counts by up to 50%, which can reduce conception rates by up to 50% in couples where the male partner is obese.  Hormonal changes are one cause of this.  The level of testosterone is reduced in obese men as testosterone is converted to oestrogen in the fat tissue.  The oestrogen produced has a negative feedback effect reducing the production of the hormone FSH.  A reduction in FSH results in a reduction in the production of sperm.

In addition, increased body fat in men is associated with raised testicular temperature which further adversely affects sperm production and function. Obese men are also twice as likely to have erection problems. Of more concern, male obesity can also affect sperm DNA integrity. If the sperm DNA is damaged (sperm DNA fragmentation) this can have a strong negative affect on both the chance of natural conception and conception with IVF treatment.  Sadly, this can also significantly increase the risk of miscarriage.

The good news is that weight loss can reverse or minimise the risks associated with obesity.  At Genea we have the Fertility Fit® program - this is a 3 month program of supervised weight loss involving a dietician and personal trainer. Of course you don’t need to do our Program, if you already are motivated or have good support.  I have seen lots of my patients conceive spontaneously or have successful IVF after losing weight.  This is very satisfying for me as a specialist.  Many of these patients came to me with heart breaking stories of multiple failed attempts at fertility treatment or multiple miscarriages. 

Around 90% of women will resume ovulation if they lose >5% of their pretreatment weight and 30% will conceive spontaneously. In very obese women this is a higher pregnancy rate than can be achieved with a single IVF cycle!  The success rates for IVF and other forms of assisted reproduction are improved. Weight loss in men also leads to an improvement in testosterone levels, sperm counts and sexual function.  My advice to patients, is to optimise their weight before moving onto any fertility treatment. Weight loss itself can be an effective treatment and many patients do conceive naturally after weight loss. The best approach is get good advice and start a program combining a change in both diet and exercise.

This article was written by Dr Antony Lighten, he is the Lead Fertility Sub-specialist at Genea’s Northwest clinic and founder of the Genea Fertility Fit® . More information on Dr Antony Lighten can be found here.