A health expert has compared new findings that 23 per cent of New Zealand women drink while pregnant as equivalent to the Zika virus for the destructive toll it takes on our children.

University of Auckland Professor of Public Health Chris Bullen said statistics that 23 per cent of Kiwi women drank in their first trimester, and 13 per cent beyond that, was "horrifying" but "not surprising" considering New Zealand's drinking culture.

Professor Bullen said, despite the high number of women drinking during their first trimester being due to the fact they don't know they're pregnant, this is actually a critical time for fetal brain development.

"It's a really sensitive time for the brain development in the baby as well as other organs, and so what we see later on in life is children with learning difficulties, children with behavioural problems, they often end up in the courts in adult life and they may be mentally impaired, and often low birth rate babies," Professor Bullen said.

"So that first trimester is really important and the problem is some women don't know they're pregnant, some women do know they're pregnant and they keep drinking, and that's a real concern, and we need to do more around that with our education programs."

Around about one per cent of the 60,000 babies born in New Zealand each year will likely have fetal alcohol spectrum disorder, causing structural anatomical problems with their face, right through to subtle learning problems and behavioural impairment.

This accounts for around 3000 babies born in New Zealand each year, which is equivalent to Zika virus' impact on America - ratio wise.

The study found there were a small proportion of women who were drinking more than four drinks per week, and some more than 20 drinks per week.

"The problem is any alcohol the women drinks during pregnancy effectively the baby's drinking at the same time and the baby doesn't have the capacity to process the alcohol in the same way an adult does," he said.