Smoking even one or two cigarettes a day before or during pregnancy is linked to health problems in newborns, warns a study that highlights the importance of quitting tobacco before conception to protect the baby.
Smoking is one of the no-nos for pregnant women, as it is associated with an increased risk of premature birth, low birth weight and restricted growth in the womb. However, what is less known is whether the timing and intensity of a mother’s smoking can affect her newborn. This is important because many women believe that it is safe to smoke before conception or in the first three months of pregnancy, or that light smoking is not harmful.
Now, new research published in the Journal of Epidemiology and Community Health has found that smoking even one or two cigarettes a day, both before conception and at any time during pregnancy, is significantly associated with major health problems in newborns. The authors say their findings reinforce the evidence that women who want to become pregnant or who are already pregnant should stop smoking to protect the health of their babies.
Although deaths and serious health problems among newborns have declined significantly, largely due to improvements in maternal care, admission to a neonatal intensive care unit remains common. Moreover, any neurodevelopmental deficits may persist into adulthood, the researchers warn.
Increased risk of serious neonatal health problems if the mother smoked
To explore this further, we analyzed national birth certificate data from the U.S. National Vital Statistics System (NVSS) from 2016 to 2019, which included a total of 15,379,982 recorded live births. After excluding multiple births, women with high blood pressure or diabetes before pregnancy, or no information on cigarette smoking in the three months prior to and during pregnancy, 12,150,535 mother-child pairs were analyzed.
Of these pairs, just over 9%, 7%, 6%, and just under 6% of mothers reported having smoked cigarettes before pregnancy, and in the first, second, and third trimesters, respectively. Smoking intensity was categorized as 0, 1-2, 3-5, 6-9, 10-19, and 20 or more cigarettes per day.
Women who smoked had more risk factors for neonatal health problems: they tended to be younger, non-Hispanic white, single, obese, less educated, had more previous births, and had fewer prenatal visits. Serious neonatal health problems were defined as need for assisted ventilation immediately after delivery; assisted ventilation for more than six hours; admission to the neonatal intensive care unit for continuous mechanical ventilation; surfactant replacement therapy; suspected sepsis; and seizures or serious neurologic problems. The prevalence of all these problems was just under 9.5%.
Smoking before pregnancy or in each of the three trimesters was associated with an increased risk of serious neonatal health problems, either separately or in combination, after adjusting for potentially influential factors such as age, ethnicity, and body mass index (BMI) before conception.
“There is no safe period or safe level of cigarette consumption shortly before or during pregnancy”
The risk of more than one serious neonatal health problem if the mother smoked before pregnancy was 27% higher, and increased by 31% to 32% if she smoked at any time during her pregnancy. And for individual components, the risk of admission to neonatal intensive care, for example, was 24% higher if the mother smoked before pregnancy, and 30% to 32% higher if she smoked during her pregnancy.
In terms of timing, women who smoked only before pregnancy or only during the first, second, or third trimester were more likely to have their newborn experience more than one serious health problem compared with women who did not smoke at any time. After adjusting for potentially influencing factors, these odds were, respectively, 12%, 23%, 40%, and 21% higher.
Even light smoking, meaning 1-2 cigarettes a day, was associated with an increased risk of serious neonatal health problems. 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. And the risk of admission to intensive care for their newborn was 13% higher with a daily consumption of 1-2 cigarettes, rising to 29% higher for 20 or more cigarettes.
The researchers acknowledge that because this was an observational study, firm conclusions about cause and effect cannot be drawn. In addition, the pre-pregnancy data did not differentiate between those who smoked at some point in the previous three months and those who smoked throughout that period. There was also no information available on exposure to secondhand tobacco smoke.
However, they conclude that their findings suggest “that there is no safe period or safe level of cigarette smoking shortly before or during pregnancy” and “reiterate the need to prevent smoking initiation in non-smokers and to promote cessation in smokers.”
