The head of a fertility clinic in Ottawa is defending its decision to bar heavily obese women from seeking in vitro fertilization.

Dr. Arthur Leader, co-founder of the Ottawa Fertility Centre, says his clinic has had a policy for over six years to deny IVF treatment to women with a Body Mass Index higher than 35.

That cutoff is well above the clinical definition of obese, which is considered a BMI over 30. (A BMI between 19 and 30 is considered healthy) The average woman who is 170 cm tall (5 foot 6) would have a BMI over 35 if she weighed more than 220 pounds. She would have a BMI of 30 if she were around 190 lbs.

Leader says the seven physicians at his clinic have agreed together that to treat a woman with a BMI over 35 is not worth the risks to the mother and child.

"(We) have agreed that the risks of the procedure, plus the risks of the pregnancy, plus the risks of an abnormal baby in obese women doesn't justify subjecting the women to IVF until they've lost enough weight to bring their BMI below 35," he told CTV News Channel Wednesday.

"We chose that based on the evidence and we've stuck to that for the last six years," he said.

Leader notes that women with BMIs over 30 are already three times more likely to have infertility problems. They are also three times more likely to have an IVF procedure fail.

He explains that the egg retrieval process of IVF is difficult in obese women because it can be hard to find their ovaries. There are also risks with the sedation used in the procedure.

Any resulting embryos are less likely to implant in the wombs of obese women and pregnancies are more likely to end in miscarriage, he says.

As well, obese women are also at higher risk of dangerous complications during pregnancy. These include preeclampsia, which is a form of high blood pressure during pregnancy, and gestational diabetes. Both pose risks to mother and baby.

"And if that weren't bad enough, studies have shown that children born to obese women through IVF are more likely to be genetically different from normal, to have heart defects and brain defects," Leader explained.

He says for that whole range of reasons, his clinic chooses not to treat very obese women. They instead encourage them to get into a weight-reduction program and come back to the clinic when their BMI has dropped below 35.

Leader admits the policy is probably a form of discrimination. But he says as doctors, he and his team have a duty of care to do no harm.

"And when you see that by going ahead with treatment that you're going to hurt somebody -- you could potentially harm the woman, you could potentially harm the embryo and the fetus -- then you have a higher duty which is to say ‘I want to avoid harm I am here to care for you'," he said.

Leader says he understands that losing weight can take a long time, and that most patients are anxious for pregnancy quickly and that the risk of infertility rises as women age. But his first interest is the safety of the woman and any of her children.

"We respect that people have the right to make their own choices but we also have a duty of care to do no harm," he said.

The president of the Canadian Fertility and Andrology Society says there will be a debate this weekend on the pros and cons of fertility treatments for obese women at a conference in Toronto.

But Dr. Carl Laskin tells The Canadian Press there are no plans to introduce a motion that would consider banning fertility treatments for women with high body mass indexes.

He says while the society is not prepared to put a policy in place, guidelines might be introduced at some point.