Raising the taxes on a pack of cigarettes by a dollar will help more than 4% of pregnant women kick the habit, new US research has found.

Researchers at Emory University and the Centers for Disease Control and Prevention looked at cigarette smoking among 225,554 women who gave birth between 2000 and 2005 in 29 states, plus New York City.

It's estimated 23% of women enter pregnancy as smokers, but the study found increasing taxes and a state's smoke-free policies helped women kick the habit and prevented them from lighting up again until, on average, four months after delivery.

"We found that a $1 increase in cigarette taxes increases the quit rate among pregnant women from 44.1% to 48.9%, a sizable effect," researcher E. Kathleen Adams said in a release about the study. "Tax policies appear to be effective in keeping these women from relapsing in the first few months postpartum, and the implementation of a full workplace smoke-free policy also increases quits."

A full ban on smoking at private worksites increased the probability of quitting smoking during pregnancy by four to five percentage points.

The study was published online Tuesday in advance of the July issue of the American Journal of Preventive Medicine.