Many more women are accessing services to help overcome or control their substance abuse during pregnancy.

But pregnant women who drink alcohol and those who use marijuana are putting their unborn babies at greater long term risk than those abusing harder drugs like ice or heroin, an expert in pediatrics at the Royal Australasian College of Physicians has said.

In the 2016-17 financial year 25 babies were born addicted to alcohol, tobacco or other drugs. The year prior there were 22 babies in that category, and in 2014-15 there were 28. According to Professor Paul Colditz, an expert in infants and babies at the Royal Australasian College of Physicians and University of Queensland, in many cases the substance abuse wouldn't be picked up at birth.

Professor Colditz said stimulants like ice and cocaine could cause miscarriage and stroke in unborn babies, and babies born addicted to methadone or heroin have severe withdrawal symptoms in the days and weeks after birth.

He said the withdrawal symptoms from methadone or heroin were severe, and often traumatic for everyone involved.

"Suddenly that supply of the drug stops when the placenta separates. The baby becomes jittery, they cry alot, they become hyperactive, they can rub their knees against the sheets so much that they become red and abrased.

"They can have seizures. It's distressing for everyone."

But babies with mums who drank alcohol or smoked marijuana suffer more in the long term, he said.

"Something like cannabis, we have evidence that it causes congenital malformations and heart and gut defects in newborns," Professor Colditz said.

"Alcohol is the biggest cause of preventable brain damage in the world."

"Everyone agrees alcohol is a toxin. The baby will be small and in particular have a small head. It kills all cells in the body, but most particularly cells in the brain - that's called fetal alcohol syndrome."

Professor Colditz said the greatest concern was that even a small amount of alcohol during pregnancy could cause these defects.

He said mothers-to-be could never be sure of the effect the alcohol was having on their unborn child, as every person metabolises it differently.

The baby of a mother who had one glass of alcohol during pregnancy compared to a mother that drank more could have the same outcomes.

Professor Colditz said babies born with fetal alcohol syndrome, or to the lesser degree fetal alcohol spectrum disorder, did not have typical withdrawal symptoms at birth, like babies on methadone.

"There is not much withdrawal at all, even for the more seriously affected babies," Professor Colditz said.

"Maybe they just go on to become the difficult child in the classroom. They have a very characteristic set of behaviours, the best example is that one of the characteristics is they end up in trouble with the law as adolescents, and not just once or twice or three times, but they're serial offenders. They cannot connect actions and consequences."

There are a number of programs run through ACT Health to help pregnant women manage their addictions.

Almost 6000 women over the past two years have accessed the ACT government's Pregnancy Enhancement Program which supports women on methadone, those who use drugs or alcohol and women experiencing mental health issues.

In addition, about 400 people including partners and family attended a program for pregnant women to address substance abuse over the past two years.

University of Canberra professor of midwifery Deborah Davis said the birth statistics were concerning.

"There is no doubt that smoking and drug and alcohol use in pregnancy is associated with poorer health outcomes," Professor Davis said.

She said it didn't help that the rate of alcohol consumption in women of a childbearing age was increasing.

"Approximately 40 per cent of pregnancies are unplanned so many women are taken by surprise by pregnancy and may not have had time to address any smoking, drug or alcohol use issues prior to becoming pregnant," she said.

"This means that we should continue to focus more broadly on health promotion in relation to substance use but also that maternity services must be well equipped to assist women with tobacco, drug or alcohol issues in pregnancy."

An ACT Health spokeswoman said the government funds preventative health campaigns including Pregnant Pause to discourage drinking alcohol and 'Quit for you, quit for two' to cut rates of smoking.

"Sadly, some women do not realise the serious health risks placed on a developing fetus when it is exposed to alcohol or drugs during pregnancy," an ACT Health spokeswoman said.

The government also funds postnatal reviews by nurses which includes management of opioid replacement therapy after the birth, drop-in midwife clinics every week, a fetal medicine unit providing care to women with complex pregnancies, and neonatology services which, among other things, monitor babies for signs of withdrawal.