Obesity is on the rise worldwide with at least 30% of adults obese and more concerningly, 17% of adolescents and children. Obesity affects every part of the body, increasing the risk of heart disease , diabetes and cancer in addition to affecting fertility.
The risk of infertility and subfertilty in the overweight is threefold higher than if normal weight; and the time taken to conceive is longer. The cumulative pregnancy rate declines 4% by every unit of BMI >29. This is similar to the impact of advancing maternal age. This is due not only to lack of ovulation but also effects on the uterine environment, embryo and egg.
The effect is even worse if both partners are over-weight as sperm production can also be impacted.
Response to treatment is poorer particularly related to central fat deposits. This applies to ovulation induction as well as IVF. It is thought to be due to metabolic disturbances such as insulin resistance and hyperleptinemia (the presence of a higher than normal amount of leptins in the bloodstream). Many studies show an impact on implantation, clinical pregnancy rates and live birth rates.
The effect on the endometrium is confirmed by studies in donor oocyte recipients. Where only eggs from normal young weight women are used implantation, pregnancy and live births rates are lower as BMI rises.
Miscarriage is more common. Pregnancy complications are higher including hypertension, pre-eclampsia, gestational diabetes, operative delivery and post-partum haemorrhage. Unexplained stillbirth rises even when diabetes and hypertension are corrected. Longer term there are epigenetic changes that can increase risk of disease in the offspring, particularly cardiovascular disease and diabetes but also cancer. This applies to risks transmitted from either parent.
Obviously weight loss is important and ideally undertaken prior to conception or Assisted Reproduction. Lifestyle modification including diet and exercise are essential. Psychosocial support is vital to long term success. Bariatric surgery may be an option for some patients.
ESHRE bulletin -Focus on Reproduction September 2013 Jose Bellver
O&G Magazine 15:4 Summer 2013. Obesity and Stillbirth pg 30.