The new Canadian Clinical Practice Guideline for the delivery of fertility care to women with obesity reviews the evidence on this very controversial topic.
Based on survey studies of fertility clinics, whether a BMI cutoff is used, and what BMI cutoff is used if so, is highly variable and not based on any specific or clear evidence. Most clinics that have an upper BMI cutoff beyond which they will not offer fertility treatments cite anesthesia risk as the main reason for the cutoff.
Not only are BMI cutoffs arbitrary and without consensus, getting below the BMI cutoff goals may be very difficult for many women with obesity to achieve. Furthermore, one study suggested that over half of the fertility clinics with a BMI cutoff did not offer any weight loss instructions or guidance to their patients – sounds to me like telling a person to row a boat but not showing them how to use the oars.
Denying fertility care to women with obesity is highly stigmatizing and discriminatory, and can worsen feelings of low self esteem, social isolation, anxiety, and depression. Denying older women fertility care until they have lost weight may cost them valuable time and any chance of pregnancy.
There is no doubt that there are risks of obesity to both the mother and the unborn child, and weight loss should be encouraged and supported. However, as the guidelines point out, the risk of obstetrical obesity-related complications does not clearly exceed the risk of complications with other pre-existing medical conditions like hypertension, diabetes, or epilepsy. In addition, obesity related health status is a better predictor of pregnancy with fertility treatment than BMI, and also a better predictor of overall health outcomes in general, so why is there so much focus on the numbers on the scale in the first place?
As the Guideline states:
In the absence of simple, safe, and effective strategies that reliably help patients with obesity lose weight in a timely fashion, it is difficult to advocate for a universal BMI cut-off in place of careful counselling, screening for metabolic abnormalities and informed consent.
Programs that impose BMI cut-offs should offer resources for patients to help them lose weight, and should inform patients about both the risks and benefits of delaying fertility treatment.