The longer a woman smokes during pregnancy, the more likely she is to have a low birth weight baby, a study by a St. Louis University epidemiologist has found.
The link between smoking and low birth weight babies has been well-established. But the study published in the Maternal and Child Health Journal is one of the first clear indications that quitting smoking during pregnancy can have health benefits for a developing fetus throughout the third trimester, said Pam Xaverius, an assistant professor of epidemiology at SLU.
“So a pregnant mom should not say, ‘Oh well, I’ve already been smoking; it’s not going to do any good now to quit,’” said Xaverius, who serves as director of the school’s maternal and child health program.
The study examined birth data from more than 183,000 Missourians who gave birth between 2010 and 2012. Unlike other previous studies, Xaverius discarded data from premature births, which frequently result in smaller babies.
Newborns who weigh less than 5 and a half pounds are more likely to have trouble gaining weight and fighting off infections, according to the March of Dimes. They’re also more likely to have long-term health problems such as diabetes or high blood pressure than those who weigh over 5 and a half pounds.
Xaverius found patients who quit smoking in the first trimester are less likely to have low birth weight babies than those who quit in the second trimester. Similarly, patients who quit in the second trimester are less likely to have low birth weight babies than those who quit in the third trimester.
That’s because the nicotine in tobacco constricts blood vessels, she said. That in turn restricts the flow of nutrients and oxygen to the placenta and the fetus. After a patient quits, that flow can be restored, she said.
The findings are particularly relevant to Missourians, Xaverius said. The state has one of the highest smoking rates among pregnant women in the country, according to the Centers for Disease Control and Prevention. More than 15% of pregnant women smoked in Missouri in 2016, a rate more than twice the national average. The state also has one of the highest maternal mortality rates in the nation, and a higher-than-average infant mortality rate.
Missouri’s low taxes on tobacco may also contribute to the number of women who smoke, Xaverius said.
“Where does Missouri fall in tobacco taxes? Dead bottom. I believe that translates into higher smoking rates,” she said. If we want to have a real impact collectively as a community, we need to decide that it’s something important.”
People who quit before becoming pregnant have the same chance of having a low birth weight baby as those who have never smoked, the study found. That's why it is important for women to receive health care before they conceive, Xaverius said.
Close to half of pregnancies are unplanned, she said. Sometimes women keep smoking after they learn they’re pregnant because they figure the damage has already been done.
“We were able to show that the earlier you quit, the better,” Xaverius said. “It’s never too late!”
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