Severely obese women should have their fertility treatment deferred until they have lost weight, according to new guidance issued by the British Fertility Society (BFS), based upon their comprehensive analysis of studies which establish the adverse impact of obesity on fertility. The report, published in the BFS journal Human Fertility, targets clinics and specialists providing care to obese women before and during pregnancy.
The guidelines adopt the World Health Organisation's weight classification system which relies upon calculating body mass index (BMI) - weight in kilograms divided by height in metres squared. Clinicians are to encourage all women to attain a 'normal' BMI, 19-24.9, before becoming pregnant and 'consider deferring' treatment of 'obese' women - BMI 30 to 34.9 - who are younger than 37 and have the time to lose weight without fear of their reproductive years ending, until their BMI is below 30 before providing treatment.
Scientific research supports that obesity dramatically hinders natural and assisted conception whilst increasing serious long-term health risks for both mother and child. Obesity is a common health problem among women of reproductive age; 56 per cent of women in the UK being either overweight or obese.
However, Dr Colin Waine, chairman of the National Obesity Forum, felt that to deny women treatment solely because of obesity is 'discriminatory' and warns of a dangerous 'slippery slope of rationing on the basis of weight' regardless of the potential benefit to overweight people. Infertility Network UK Chief Executive Claire Brown advocated an individual, 'flexible approach' because infertility is stressful and numerous factors that affect fertility also affect weight.
Dr Mohammed Taranissi, a leading London fertility expert, opposed the guidelines: 'They are factually incorrect and based on bad science. BMI is not very accurate, particularly for women who have a lot of muscle. It's important to look at the range of factors and treat women as individuals, not just take weight as the be-all and end-all'. Yet studies show that women with a BMI above 35 are half as likely to become pregnant than women with a BMI below 30. Fat interferes with hormones which regulate ovulation and often weight-loss can increase chances of pregnancy. The BFS report states that overweight infertile women generally need to lose only 5-10 per cent of their body weight to be able to successfully conceive naturally.
The BFS guidance further recommends that clinics should assist obese women in their weight-loss including psychological support, dietary advice, exercise classes and, in more extreme cases, weight-reducing drugs or gastric surgery. BFS guidelines are not legally binding but are expected to be incorporated next year into the official recommendations of the National Institute for Health and Clinical Excellence.