Weight and Fertility

There is a progressive rise in the incidence of obesity in the developed world, and about 60% of Australian adults are overweight. Obesity is associated with a number of health problems, including diabetes, high blood pressure, heart disease and high cholesterol. Moreover, obesity is associated with an increased risk of certain cancers including of the breast, ovary and colon.

Being markedly over or under weight also decreases fertility rates and may reduce the likelihood of fertility treatment being successful. Being overweight can also increase the risk of problems in pregnancy including miscarriage, high blood pressure and the baby being born with a physical abnormality.

For obese women, even a moderate weight loss of between 5% and 10% can significantly improve fertility and reduce pregnancy risks.

Being underweight can also have a negative impact on fertility. This may be why women who have a history of anorexia and bulimia are twice as likely to require fertility treatment in order to become pregnant.

How can I tell if my weight is in the ideal range?

The most widely accepted method of assessing if someone is in the ideal weight range is to calculate their Body Mass Index (BMI). Your BMI is calculated as your weight in kg divided by your height in metres². This index of weight to height is designed for men and women over the age of 18. A healthy BMI lies between 18.5 and 24.9. A BMI of below 18.5 indicates that you may be underweight and a BMI of above 24.9 suggests that you are overweight. Several BMI calculators are available on the internet.

Why is Weight Associated with Fertility?

The link between obesity and infertility is not yet fully understood as even if women ovulates regularly and all fertility tests are normal, obesity is still associated with reduced fertility rates and some studies suggest with a lower chance that fertility treatments such as in-vitro fertilization (IVF) will be successful.

There is a gland in your brain called the hypothalamus that tracks your body's nutritional status. The hypothalamus is linked to your pituitary gland which controls whether you ovulate (produce an egg). If your hypothalamus detects that your nutritional status is not ideal for becoming pregnant then this may prevent the message to ovulate being sent to your ovaries. Another possible mechanism for a link between obesity and reduced fertility is that insulin levels in the blood stream may increase in women who are overweight and this can be associated with the development of polycystic ovary syndrome.

Weight and the Success Rate of Fertility Treatment

Studies differ on whether being overweight reduces the success rate of treatment. Some studies suggest that women who are obese have about half the pregnancy/success rates following treatments such as IVF, when compared to women who have a normal BMI. There are many possible reasons for this. Obesity appears to be associated with longer treatment and increased medication requirements. For this reason, a number of national fertility guidelines such as those in the USA and UK suggest that women should have a BMI of below 35 (and ideally below 30) before fertility treatment is commenced.

Weight and Risks during Pregnancy

Obesity can have an impact on risks during pregnancy in two main ways. First, there is a greater chance of having a maternal complication during pregnancy such as high blood pressure (hypertension) and diabetes (gestational diabetes). Secondly, there is a greater risk to the pregnancy/baby, including some evidence of increased rates of miscarriage, a possible increased risk of stillbirth and a higher risk of the baby being born with a range of physical abnormalities including spina bifida and hydrocephalus, and heart defects. Where a woman is obese, the risk of such an abnormality may be as high as 10%, but if she loses weight and her BMI returns to the normal range before becoming pregnant then studies suggest that the risk of a baby being born with a physical abnormality falls and may become approximately the same as the average for the general population.

Weight and Risk of Anaesthesia

Women undergoing IVF will require an anaesthetic or sedation during the egg collection procedure. Women who are pregnant may also need a caesarean section in order to deliver the baby. The risks associated with anaesthesia increase significantly if a woman is obese.

Strategies for Weight Loss

1. Build a support network that could include a counsellor and your GP in order to get regular feedback and encouragement

2. Negotiate a target weight that is achievable with your fertility specialist. Remember a weight loss of 5% can have a significant impact on your fertility and the chance that treatments such as IVF will be successful

3. Consult an accredited dietician

4. Seek advice from your GP about the best approaches to exercise for losing weight. Lifestyle modification, including diet and regular exercise are an essential component of a successful weight loss program. National guidelines for exercise and diet can be found at;

There are a number of lifestyle programs available to support you and give you advice. At Monash IVF and Bubtree you can see our counsellor Antonia and/or enrol in our lifestyle and fertility program.

Weight Loss (Bariatric "Lap Band) Surgery and Fertility

If attempts at lifestyle modification have not been successful in leading to adequate weight loss then there is some evidence that women who have a very high BMI may increase their chances of getting pregnant and reduced their risk of pregnancy complications by having bariatric surgery, provided that they maintain an adequate diet and take appropriate vitamin supplements. The Scientific Advisory Committee of the Royal College of Obstetricians and Gynaecologists (RCOG) published a detailed review of the role of bariatric surgery and fertility in March 2010. This review suggested that there may be a role for bariatric surgery in women who have a BMI of greater than 40 or who have a BMI of greater than 30 and have other significant health problems (so called co-morbidities).