Since the 1990s, rates of sudden infant death syndrome (SIDS) have halved. Parents were widely encouraged to put their babies to bed on their backs and to clear cribs of potentially suffocating materials, and the efforts worked. But as those accidental deaths dropped out of the statistics, another factor became increasingly important: smoking.
Severalstudies in the intervening years have concluded that smoking is the biggest preventable risk factor for SIDS. Many of these studies have quantified how much more likely a baby is to die of SIDS if their parent smoked while pregnant—it ranges from roughly 1.5- to 6.5-fold higher—but they mostly look across broad groups. Nine months is a long time. Could quitting halfway through help, or is the damage already done in the first trimester? Researchers at the Seattle Children’s Research Institute decided to look in more detail, and recently published their results in the journal Pediatrics.
In looking at more than 12 million births between 2007 and 2011, the researchers found that every cigarette mattered. The difference between not smoking at all and smoking one a day was a twofold increase in SIDS risk, and every cigarette after that added another 0.07 to that risk. (Though it's important to note that the overall risk of SIDS is low, at just 0.83 per 1,000 live births, so even a doubled risk is less than 2 in 1,000). Those who smoked all the way through—about nine percent of the study subjects—had offspring with a 2.52-fold higher risk of SIDS. Half of those patients didn’t reduce their smoking at all, but those who did helped their baby with each cigarette they avoided. People who were able to smoke less by the third trimester could decrease their risk elevation by 12 percent, while quitting entirely in that period resulted in a 23 percent risk reduction.
The curve plateaued after 20 cigarettes a day, so people who smoke more than a pack daily aren't seeing a huge benefit if they merely get themselves down to a pack. People who smoke less than one pack per day are the ones most likely to see a significant change in SIDS risk by reducing their habit.
Researchers still aren’t entirely sure how smoking increases SIDS risk. The study notes that evidence so far points to changes in serotonin and other neurotransmitters in the brainstem of a growing fetus, which smoking has been linked to. Nicotine seems to influence serotonin release in animal studies, supporting that claim. But even without a solid mechanism, this study and others show that smoking is a huge risk factor for SIDS. These researchers estimate that 22 percent of all SIDS cases could be caused by smoking during pregnancy. It's impossible to prove that without knowing the mechanism behind those deaths, but that figure represents 800 infant mortalities a year.
Although the number of women who smoke before getting pregnant is low, at just 11.6 percent in the U.S., three-quarters of them continue to smoke during pregnancy. And unfortunately, even those in the recent study who quit smoking before getting pregnant had a 1.47-times higher risk of their baby developing SIDS than did subjects who never smoked. One study estimated a similar rise in risk simply from inhaling smoke secondhand. In fact, the Centers for Disease Control notes that inhaling any tobacco smoke makes offspring more likely to weigh less at birth, to have ear infections, and to have more frequent asthma attacks.
Pregnant people tend to get a lot of grief for indulging in habits that are unhealthy for all of us, which is far from fair. But babies aside, smoking puts you at much higher risk of heart disease, stroke, chronic obstructive pulmonary disease, and at least a dozen types of cancer—if no one smoked in America, one in three cancer deaths wouldn’t happen. You have plenty of reasons to quit smoking that have nothing to do with the health of any hypothetical children you might carry one day. But if you're pregnant or trying to become pregnant and need some motivation, know that any effort you can make to cut down on your habit could pay off.