Less than 10% of women continued to smoke at any point during pregnancy, and less than a quarter of those reported quitting later in the pregnancy, according to 2014 birth certificate data released by the CDC.
Overall, 8.4% of women said they smoked at any point during pregnancy, with 20.6% of women who smoked during the first or second trimesters quitting by the third trimester, reported Sally C. Curtin, MA, and T.J. Matthews, MS, both of the CDC.
In fact, the majority of women (72.0%) who did quit smoking during pregnancy did so between the first and second trimesters, they wrote in the National Vital Statistics Report.
"Smoking during pregnancy is considered to be one of the most modifiable risk factors associated with poor birth outcomes," they wrote. "A Healthy People 2020 goal is for the prenatal abstinence rate to improve by 10% by the year 2020, to 98.6%."
Not surprisingly, low socioeconomic status was linked with smoking during pregnancy. There were 14.1% of pregnant women with less than a high school education, 14.0% of those with Medicaid insurance, and 12.6% receiving WIC benefits who reported smoking. Unmarried women (14.7%) and younger women ages 20-24 (13.0%) had similar rates of smoking.
"Many of these demographic factors are interrelated; for example, the majority of women who give birth in their early 20s are unmarried," the authors wrote.
Demographically, the highest rates of smoking during pregnancy occurred among non-Hispanic American-Indian or Alaskan-native women (18.0%).
Early prenatal care also seemed to protect against smoking during pregnancy, with only 7.1% of women receiving prenatal care during the first and second trimester reporting smoking compared with 14.6% of patients who had no care or only had care in the third trimester.
Conversely, higher education and income was linked to the likelihood of women quitting smoking while they were pregnant. Over a third of women with a bachelor's degree or higher (36.4%) and 28.4% of women with private insurance stopped smoking during pregnancy. Demographically, pregnant women who were non-Hispanic Asian (36.3%) and Hispanic (32.3%) were the most likely to quit.
Interestingly, while teenagers had the second highest rate of maternal smoking during pregnancy (10.1%), they also had the highest rates of smoking cessation (27.2%).
Examining smoking rates in the pre-conception period, there were 10.9% of women who reported smoking in the 3 months prior to pregnancy, though about a quarter (24.2%) of these women did not smoke during pregnancy.
Researchers collected data based on the 2003 revision to the birth certificate for 46 states and the District of Columbia, which collects data on smoking before and during pregnancy. This represents 95% of all births in the U.S.
The authors note that despite improved reporting, prevalence of smoking during pregnancy may still be underestimated. In fact, one study showed that maternal smoking before and during pregnancy was 25% lower on the birth certificate compared to medical records, especially among more educated women with fewer children who were not WIC recipients.
"These women may perceive more of a stigma to admitting to smoking before and during pregnancy than their less-educated counterparts," the authors wrote.