Canberra doctors are split over suggestions of an in vitro fertilisation age cap after a British woman said her IVF baby, conceived when she was 57, was a mistake.

Professor Stephen Robson is almost 50 and has a four-year-old daughter, so he is hesitant to put an age limit on motherhood.

But the Associate Professor of Obstetrics and Gynaecology at the Australian National University Medical School said he would support government legislation to limit access to IVF for women over 50.

The discussion started after a British woman who conceived her daughter through in vitro fertilisation in 2008, was widely criticised for being too old to have a child.

But now faced with the challenges of raising a three-year-old alone at the age of 61, she says there should be an age limit of 50 for women seeking IVF treatment.

Professor Robson's oldest IVF patient was 50.

''It was complex but she had babies and it was incredibly satisfying,'' Professor Robson said.

The fertility specialist said older women often made better mothers.

''When they do get on with it they are just so motivated.''

There is no age limit on IVF in the ACT, but in South Australia, where Professor Robson trained, guidelines suggest 50.

It's a stance Professor Robson supports. He said women over the age of natural menopause (50 and over) should only be given IVF treatment in extraordinary circumstances.

''Sometimes the stories are heartbreaking and your natural inclination is to try to help as much as you can, but helping also means not giving unrealistic expectations and just doing what people want.

Professor Robson said most women over the age of 43 have to use their own previously frozen eggs or an egg donor to conceive - even with IVF.

''In reality it's very hard for women to get pregnant over the age of 43 - that's a natural barrier; women are born with all their eggs and often the mechanism for them to function just gets too old,'' Professor Robson said. He said women who undergo IVF before the age of 30 have a 40 per cent chance of a live birth. After 37 this drops to 25 per cent and after the age of 40 there is a 10 per cent chance of a live birth following multiple IVF treatments.

But Canberra obstetrician Tween Low said clinical decisions should be left to doctors. The fertility specialist said her oldest patient was in her late 40s.

''I have seen women over the age of 50 but I haven't helped them get pregnant,'' Dr Low said.

''I don't think authorities can be prescriptive in saying what age should be the cut-off for having a baby. Each individual is different.''