Smoking during pregnancy is known to raise the risk of preterm delivery, low birth weight, and restricted growth of the fetus. But can light smoking during pregnancy, just one or two cigarettes, still harm the newborn?

A study published in Journal of Epidemiology and Community Health suggests "that there is no safe period and no safe level of cigarette smoking shortly before or during pregnancy." The new study provides further evidence of the harmful effects of smoking during pregnancy, emphasizing the need to completely quit the habit for the baby's health.

The research team utilized data from the US National Vital Statistics System (NVSS) that has recorded a total of 15,379,982 live births between 2016 and 2019. After filtering out factors such as multiple births, high blood pressure or diabetes before pregnancy, and lack of information on the smoking status 3 months before and during their pregnancy, the researchers narrowed it down to 12,150,535 mother-infant pairs.

The study noted that over 9% of them reported smoking cigarettes before pregnancy, 7% during the first trimester, 6% in the second trimester, and around 6% in the third trimester. The intensity of smoking was measured based on the number of cigarettes smoked per day: 0, 1–2, 3–5, 6–9, 10–19, and 20 or more.

"The women who smoked had more risk factors for neonatal health issues: they tended to be younger, non-Hispanic White, unmarried, and obese, and to have low educational attainment, more previous births, and fewer attendances for prenatal care," the news release stated.

The estimated prevalence of neonatal health issues was around 9.5%. Neonatal health issues included cases where newborns required immediate assisted ventilation, ventilation for more than 6 hours, NICU admission for continuous mechanical ventilation, surfactant replacement therapy, as well as cases of suspected sepsis, seizures, or serious neurological problems.

"Smoking either before pregnancy or in each of the 3 trimesters of pregnancy was associated with an increased risk of major neonatal health issues, either separately or combined, after adjusting for potentially influential factors, including age, ethnicity, and weight (BMI) before pregnancy," the news release stated.

In cases where expectant mothers smoked before pregnancy, there was more 27% higher risk of having more than one major neonatal health issue. The risk was 31-32% higher if she smoked at any time during her pregnancy.

When compared to expectant mothers who did not smoke at all, both smoking before pregnancy and during any point of pregnancy puts newborns at higher risk of having more than one health issue.

"Even light smoking—1–2 cigarettes a day—was associated with a heightened risk of major neonatal health issues. For example, among mothers who smoked 1–2 cigarettes a day before pregnancy, the risk was 16% higher, rising to 31% higher if they smoked 20 or more a day," the news release stated.

When an expectant mother smokes just one or two cigarettes a day, the newborn's risk of admission to intensive care is 13% higher. This risk increases to 29% for those who smoke 20 or more cigarettes daily.

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