Published on Monday in the journal Pediatrics, an analyzed data on smoking during pregnancy from the US Centers for Disease Control and Prevention's birth/infant death data that was set between 2007 and 2011 showed that the risk of death rises by .07 for each additional cigarette that a pregnant woman smoked.

The study found out that by the time a pregnant woman smokes a pack a day, the baby's risk of unexpected sudden death has tripled compared to infants whose mothers don't smoke.

"One of the most compelling and most important points that I would take away from the study is that even smoking one or two cigarettes still had an effect on sudden infant death," said pulmonologist Dr. Cedric "Jamie" Rutland, a national spokesman for the American Lung Association. 

Every cigarette counts," said lead study author Tatiana Anderson, a neuroscientist at the Seattle Children's Research Institute. "And doctors should be having these conversations with their patients and saying, 'Look, you should quit. That's your best odds for decreasing sudden infant death. But if you can't, every cigarette that you can reduce does help.' "

SIDS or sudden infant death syndrome was an unexplained and frightening phenomenon for decades until researchers were able to connect the baby's sleeping position and the sudden rise of infant deaths. If babies between 1 month and 1 year of age were put to sleep on their stomachs, the risk of them dying of SIDS is doubled, according to the American Academy of Pediatrics.

A "back to sleep" campaign was launched in 1994 and it educated the parents about the cause of SIDS and the deaths dropped by about 50% when parents began putting their babies to sleep on their backs. By 2010, the rates of SIDS in the United States have fallen to about 2,000 a year, according to the American Academy of Pediatrics.

But while the number of infants dying because of SIDS has fallen, there is another type of sudden infant death that has risen over the past two decades. Research has shown a direct link between a mother's smoking and the sudden infant death.

"Women know they shouldn't be smoking during pregnancy, and there is a certain population that either denies that they smoke or underestimates the number of cigarettes they smoke," Anderson said.

 According to the American College of Obstetricians and Gynecologists, around 23% to 34% of SIDS cases and around 5% to 7% of preterm-related infant deaths can be connected to prenatal smoking.

"That's the other take-home message," Anderson said: "Women who are planning on getting pregnant and are smokers should quit well before they even try to get pregnant because smoking in the first three months before you get pregnant can have a detrimental effect."