Women who give birth in their 50s are just as able to cope with motherhood as younger women, according to a study by fertility specialists. Surveys of older women having fertility treatment showed they found parenting no more stressful or physically demanding than women in their 30s and 40s, and they showed no signs of poorer mental health possibly brought on by feelings of isolation.

The findings counter views that older women may make less suitable mothers and follows recommendations from the head of the government's fertility watchdog, Lord Harries of Pentregarth, the former Bishop of Oxford, that women in their 50s and 60s should not be barred from having IVF on account of their age.

There is no official age limit for IVF in Britain, but the NHS refuses to fund treatment for women over the age of 40, and many private clinics are unwilling to treat women older than 45 years.

Poor success rates and legislation that requires doctors to take into account the welfare of children born to IVF, lead to most clinics rejecting older women even if they plan to use eggs from younger women. Above the age of 45, women have twice the risk of stillbirth and ectopic pregnancy. Rates of pre-eclampsia and diabetes roughly triple for women over 55.

In July, Patricia Rashbrook, a child psychiatrist, became the oldest woman in Britain to have a baby. She had the child, a 6lb 10oz boy, by caesarean section, aged 62 after receiving fertility treatment in eastern Europe. She was criticised by a number of pressure groups who pointed out she would be in her 70s when the child reached his teens.

Anne Steiner, at the University of North Carolina, and Richard Paulson, at the University of Southern California, carried out surveys measuring parental stress and the mental and physical health of women who conceived over the age of 50 after treatment with donor eggs, and compared these women with others in their 30s and 40s who had conceived through IVF at the same time.

In the stress survey, women were asked questions such as whether they found it harder than expected to get their children to behave, and whether they thought their children cried more than others. To assess the mental and physical demands of parenting, the women were asked whether they often felt isolated and friendless, and how far they could walk without discomfort.

The surveys were completed by 64 women and showed those their 50s were no different in mental or physical health compared with those in their 30s and 40s. Parental stress was found to be lowest among women in their 30s and highest among those in their 40s, with those in their 50s ranking in between.

Dr Steiner, who will present the findings today at the annual meeting of the American Society for Reproductive Medicine in New Orleans, said: "The conclusion ... is that if we look from the perspective of stress and physical and mental functioning, it doesn't seem we can restrict parenting based on these reasons." She said many of the older women were married to significantly younger men, a factor that might have helped reduce the stress of motherhood, and they were financially comfortable. Their children were also no older than 12.

Gillian Lockwood, medical director at Midland Fertility Services, said the research supported decisions by some women to have children later in life. "I don't agree with the view that men may father a child into their late 80s, but it's wrong for women to want to extend their fertility after 45. That's ageist and sexist."