By Sandee LaMotte, CNN

(CNN) -- Smoking even one cigarette a day during pregnancy can double the chance of sudden unexpected death for your baby, according to a new study analyzing over 20 million births, including over 19,000 unexpected infant deaths.

The study, published Monday in the journal Pediatrics, analyzed data on smoking during pregnancy from the US Centers for Disease Control and Prevention's birth/infant death data set between 2007 and 2011 and found that the risk of death rises by .07 for each additional cigarette smoked, up to 20 a day, a typical pack of cigarettes.

By the time you smoke a pack a day, the study found, your baby's risk of unexpected sudden death has nearly tripled compared with infants of nonsmokers.

"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 and SUID

Sudden infant death syndrome, known as SIDS, was a frightening, unexplained phenomenon for parents for decades until research discovered a connection between a baby's sleeping position and the sudden deaths. If babies between 1 month and 1 year of age were put to sleep on their stomachs, the risk of dying of SIDS doubled, according to the American Academy of Pediatrics.

The introduction of the "back to sleep" campaign in 1994 educated parents about the dangers, and the rate of deaths dropped by about 50% when parents began putting babies to sleep on their backs. That was soon followed by recommendations to remove bumpers, blankets, toys and other potentially suffocating clutter from the crib.

By 2010, the rates of SIDS in the United States had fallen to about 2,000 a year, compared with nearly 4,700 in 1993, the American Academy of Pediatrics says.

But while the numbers of babies dying of SIDS decreased, two other types of sudden infant death -- ill-defined causes and accidental suffocation -- have risen over the past two decades, Anderson said, bringing total deaths to approximately 3,700 a year.

Today, researchers combine the three types of death and call it SUID, short for sudden unexpected infant death.

The link to smoking

Research has shown a direct link between mother's smoking and SUID. According to the American College of Obstetricians and Gynecologists, 23% to 34% cases of SIDS and 5% to 7% of preterm-related infant deaths can be attributed to prenatal smoking.

The costs to children born to smokers are also high. Research has shown a connection between smoking during pregnancy and a higher risk of asthma, infantile colic and childhood obesity. Even secondhand smoke is dangerous to the developing fetus, increasing the risk of low birth weight by as much as 20%.

Just how smoking contributes to SUID is being heavily researched, but a prevailing theory is that it increases levels of serotonin, a neurotransmitter that plays a key role in behavioral arousal and activity. In susceptible infants, it's possible that serotonin affects the ability of the brain stem to regulate the respiratory system during sleep.

"And maybe that leads to the infant stopping to breathe at night," said Rutland, who is also an assistant clinical professor of internal medicine at the University of California's UCRiverside School of Medicine.

Rates of smoking in pregnancy still high

Despite a significant drop in smoking rates in the United States, Anderson says, self-reported statistics show that about 338,000 women smoke during pregnancy each year.

"These numbers are probably on the conservative side," Anderson said. "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."

Despite the knowledge that smoking can harm their baby, Anderson said, statistics show that 55% of those 338,000 pregnant women are unwilling or unable to stop.

"They do not reduce or quit smoking," she said. "They just continue smoking at the same rate throughout their pregnancy."

Yet if no women smoked during pregnancy, the study's computational models estimate, 800 infant deaths each year could be avoided, Anderson said.

Smoking before pregnancy

The new research, the first to be done in conjunction with Microsoft data scientists who volunteer their time as part of the Aaron Matthew SIDS Research Guild, was also the first to look at the impact of smoking before pregnancy.

It wasn't good news for women who smoke and suddenly find out that they are pregnant.

"If you smoke in the three months before pregnancy and quit by the end of the first trimester, you have more than a 50% greater risk of SUID compared to nonsmokers," Anderson said.

That risk is still lower than if you smoked throughout pregnancy, she explained, but the overall risk is greater than for those who smoked only before pregnancy or never smoked at all.

"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."

For Rutland, the pulmonologist, that makes sense.

"What it tells you is that when you smoke a cigarette, the physiologic consequences don't stop just because you quit for several weeks," he said. "It just shows you how powerful something like smoking is and the lasting effects it can have on your body."

Reducing risk

Many women who want to stop smoking for the baby's health find it's harder than they thought it would be, said Laurie Adams, founder and executive director of Baby & Me Tobacco Free Program, a smoking cessation program.

"What we find nowadays is that there are fewer women who are casual or social smokers," Adams said. "The level of nicotine in most cigarettes really has hooked them. And so most of the women that we serve that are daily smokers, smoking anywhere from a half to a pack of cigarettes a day. They're definitely hooked."

Women who want to use FDA-approved smoking cessation products should be aware that most are safe during pregnancy, Rutland said.

"The only one that we say is not safe during pregnancy is Chantix, and that's just because it hasn't been studied, " Rutland said. "Wellbutrin [bupropion] and the nicotine replacement strategies such as the nicotine-replacement gum and patch are safe."

For women who want to use non-medical approaches, evidence-based counseling and support techniques are available through the CDC's Office on Smoking and Health. There are smoking quit-line services in all 50 states that can be accessed via a toll-free national portal provided by the National Cancer Institute at 1-800-QUIT NOW.

A counseling-based program, like Baby and Me, will often focus on a positive approach, offering information and support to prepare a woman for what she will experience during nicotine withdrawal, Adams said.

"We'll help her set up a quit plan," she said. "We'll give her things to do instead of smoking when the urge hits, such as deep breathing, drinking water to flush out toxins and reaching out to a support system. We'll teach her how to reduce stress and avoid triggers."

The important thing for women in this situation is to reach out and get help, Adams stressed.

"They can break free from this nicotine addiction," Adams said. "Not only can they have a healthy baby born on time, they can continue their recovery and not go back to smoking so that the risk of SUID is dramatically reduced."