Women in Victoria's north-west might need to travel as far as Melbourne or Adelaide to give birth after a Mildura hospital announced changes to its birthing guidelines.

Under new rules at Mildura Base Hospital, women with a body mass index (BMI) of 50 or more are no longer able to give birth at the hospital, except in the case of an emergency.

Meanwhile, expectant mothers with a BMI between 40 and 49 will be treated on a case-by-case basis.

The hospital's director of nursing Janet Hicks said the change was about giving women the best care possible.

"The evidence demonstrates that those women who fall into those high risk categories really should be referred to a tertiary hospital or a hospital with a higher level of care," Ms Hicks said.

"All pregnancies are different and complications can arise in any pregnancy so we believe it's the safest option."

Ms Hicks said while antenatal care services would remain unchanged, women would have to birth at specialist neonatal intensive care units in either Melbourne, Bendigo or Adelaide.

The hospital's director of obstetrics and gynaecology, Dr Ian Pettigrew, has denied the change was a downgrade of hospital services.

"It's a very practical approach to a problem that is creating problems within services across the whole of Australia," Dr Pettigrew said.

"Women with a BMI over 40 have a very high risk of developing complications such as pre-eclampsia, accidental haemorrhage, where there's bleeding behind the placenta and growth restriction, where the babies don't grow adequately.

"If a woman has a BMI of over 50 they probably have at least a 50 per cent chance of having a caesarean section with all the risks associated with that."

Bus travel for pregnant women to city 'not preferred'

Dr Pettigrew said some heavily pregnant, obese women could travel by bus to the city if they did not have other transport, a suggestion Dr Alexis Shub, a Melbourne University lecturer specialising in obstetrics, labelled not ideal.

"I think that long, sedentary travel for obese women in late pregnancy does carry increased risk of deep vein thrombosis similar to that associated with long plane flights," Dr Shub said.

"It wouldn't be my recommendation for a woman to travel in that way."

But Dr Shub said if women preferred to take the bus, precautions such as regular stretching were important to reduce the risks associated with long travel periods.

She said there were subsidy schemes to support women who needed to travel to give birth.

"One of the troubles of the scheme is that women are required to pay up front and then have the money reimbursed and obviously, that's difficult for some people," Dr Shub said

"Although, I understand that Mildura [Base Hospital] has been able to support women and help them when that's a problem.

"But I think the bus is probably not the preferred method of travel for these women."

A spokesman for the Department of Health said the changes were brought in place to minimise the risks to both mother and baby during childbirth.

He said it was prompted by a review into neonatal deaths at the Bacchus Marsh maternity unit of the Djerriwarrh Health Service in 2013 and 2014.