A Large Study Highlights the Dangers of Smoking During Pregnancy

Research has long shown that smoking during pregnancy can greatly increase the risks of birth defects.A new study analyzing the outcomes of more than 9 million participants provides further evidence of the adverse outcomes associated with tobacco use during pregnancy.

The study, published in the Journal of Perinatal Medicine, examined the delivery outcomes in over 400,000 smokers and 8.6 million non-smokers in the United States between 2004 and 2014. 

Researchers found that pregnant people who smoked had a 130% increased risk of having a baby that was too small for its developmental stage—heightening the risk of intestinal and urinary disorders, lung problems, and adverse neurological outcomes in childhood.

They also discovered a 40% increased risk of premature birth and a 50% increased risk of rupturing the amniotic sac surrounding the fetus before labor begins.

“Smoking is also associated with congenital malformations and has a negative impact on fetal neurocognitive development,” Ido Feferkorn, MD, a researcher at the McGill University Health Care Center and a co-author of the study, tells Verywell. “Regarding complications to the mother, an increased risk of wound complications and the need for hysterectomy among the smokers was found.”

While many studies have shown that smoking during pregnancy can lead to a damaged placenta, undernourished baby, and even stillbirth, this new research examined complications that were only studied in smaller samples.

“The study is impressive because of its size,” Caitlin Dunne, MD, a fertility specialist and co-director of the Pacific Centre for Reproductive Medicine (PCRM), tells Verywell. “In a practical sense, this data matters to doctors because we know more about what to look out for as we care for pregnant patients.”

Smoking Reduced Certain Risks Slightly, But It Doesn’t Mean You Should Start

Interestingly enough, researchers found that smokers had reduced rates of preeclampsia—a pregnancy complication characterized by high blood pressure and liver or kidney damage. If left untreated, preeclampsia could lead to premature births or the need for C-section.

But researchers warned that the lower rate of preeclampsia could simply be related to lower birth weight of the babies among smokers.

The risks associated with smoking during pregnancy still far outweigh any perceived “benefits," Dunne explains.

“I should point out that this does not mean that the authors believe smoking is beneficial,” she says. “These findings may just be a consequence of doing a very large database study without having detailed information about the context of each pregnancy.” 

Dunne also points out that large association studies like this one don't necessarily infer causation, but they can help guide future research that will hone in on the finer details of cause and effect.

Both Feferkorn and Dunne say that while quitting smoking is undeniably difficult, it’s an essential step in ensuring your baby’s well-being.

“I tell my patients: Do your best to quit or cut down on cigarette smoking or vaping. I know that quitting is hard and it often takes many attempts to kick the habit. Don’t be too hard on yourself—just keep trying,” Dunne says. “Quitting smoking is one of the best things you can do for the baby’s health. It’s worth the effort.”