A drop in the number of women who smoke while pregnant has helped push down the number of infants going into hospital, according to researchers.

A study of all 788,798 children born in New South Wales between 2001 and 2009, published in the Medical Journal of Australia, shows a 10.5% drop in the number of infants under a year old being re-admitted to hospital, from 18.4 per 100 births in 2001 to 16.5 in 2009.

The report, authored by researchers from the University of NSW, Royal North Shore Hospital and Sydney Medical School, states 55% of this decrease can be attributed to just a few changes.

The increasing average age of mothers at the time of giving birth, improved hospital care and a fall in smoking rates while pregnant are cited as key improvements in infant health.

The proportion of infants born to mothers who smoked decreased from 17% to 12% during the study period.

“Maternal smoking rates have been declining over the past 15 years in Australia,” the study states.

“Older mothers are less likely to smoke during pregnancy, while mothers who attend antenatal care earlier in their pregnancy are more likely to stop smoking.”

Numerous public health campaigns over the past decade have warned women about the dangers of smoking when pregnant.

According to the federal government’s Quit Now project, referencing US department of health data, smoking when pregnant increases the chances of premature birth, low birth weight, stillbirth and infant mortality.

The amount of oxygen flowing to unborn babies is restricted due to nicotine and other chemicals found in tobacco smoke, which is passed to them through the placenta, narrowing blood vessels. Women can also pass nicotine onto their offspring via their breast milk, according to US research.

Cancer Council NSW said its own statistics showed that smoking rates among pregnant women in the state had fallen further since the study period, with 10.4% of expectant mothers smoking in 2012.

Cancer Council Queensland said maternal smoking rates in Queensland had also dropped, from 20% in 2006 to 15% in 2012.

“This is encouraging research that highlights the value of federal and state government action on tobacco control,” said Katie Clift, spokeswoman for Cancer Council Queensland.

“If these trends are mirrored in Queensland, we can expect to see healthier mums and bubs, and fewer smoking-related health complications during pregnancy and after birth.

“Smoking during pregnancy causes a range of complications including an increased risk of miscarriage, premature birth, Sids and the likelihood a child will have problems with lung development and lung function.

“The urgent introduction of smoke-free public places, including bus stops, taxi ranks, ferry terminals and pedestrian malls, is a crucial strategy to help further reduce the maternal smoking rate.”

The tobacco industry has warned the ban on branding or logos on packets will see an influx of cheap cigarettes from abroad, potentially pushing up smoking rates. Overall smoking rates have been in steady decline across Australia since 2001, however, including the period of the plain packaging laws.