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Children whose mothers used snus — a type of powdered, smokeless tobacco popular in Sweden — during pregnancy had higher blood pressure by age 6 than children whose mothers did not use it, new research says.

Snus is placed between the gums and upper lip, but unlike American chewing tobacco, it does not involve spitting. The European Union banned its sale in 1992 after a World Health Organization study concluded it caused cancer. It is available in the U.S., where the Food and Drug Administration is reviewing it.

Previous studies have linked smoking during pregnancy to preterm birth, low birth weight and stillbirth. Studies also have found children exposed to smoking while in utero have higher blood pressure.

But those studies could not separate the effect of nicotine from the effect of other smoking-related byproducts. They also could not control for the secondhand smoke many children of tobacco smokers are exposed to.

The new study, published Wednesday in the , isolated nicotine's effects by studying women who used only Swedish snus.

Researchers compared blood pressure and heart rate in 21 children ages 5 to 6 whose mothers used snus during pregnancy with 19 children whose mothers used no tobacco products.

The systolic blood pressure — the top number in a blood pressure reading — of the children exposed to snus was 4.2 millimeters of mercury higher than the children with no nicotine exposure.  

Nicotine easily passes through the placenta and reaches the developing fetus, the study's lead author, Dr. Felicia Nordenstam, said in a news release. She's senior consultant in pediatric cardiology at Karolinska Institutet University Hospital in Stockholm.

"Although the increase in blood pressure is not clinically significant for an individual child, because blood pressure generally follows an upward trajectory throughout an individual's life, it may increase more quickly to a point of clinical significance during adulthood, especially if paired with other risk factors such as obesity or inactivity," she said.

Women should avoid all tobacco products during pregnancy, Nordenstam said.

"Nicotine use during pregnancy, regardless of whether it is in snus, cigarettes, smoked tobacco or vaped tobacco products, is not safe and may have a negative impact on the future health of the child."

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