Effects Of Secondhand Smoke On Pregnancy: Women Of Childbearing Age May Risk Poor Fetal Brain Development Even Before Conception

Women are advised to quit smoking once they become pregnant to protect their health, and their baby's health. Quitting smoking may not be enough to reduce risks associated with cigarettes, such as miscarriage, low birth weight, and even Sudden Infant Death Syndrome (SIDS). Researchers at Duke University found exposure to secondhand smoke can lead to fetal brain development impairment, even before a woman gets pregnant.

"This finding has important implications for public health, because it reinforces the need to avoid secondhand smoke exposure not only during pregnancy, but also in the period prior to conception, or generally for women of childbearing age," said Theodore A. Slotkin, Ph.D., professor in Duke's Department Pharmacology & Cancer Biology, in a statement.

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Secondhand smoking refers to the product released into the air whenever someone who is smoking exhales. This can also come from the end of tobacco products. There are approximately 4,000 chemicals in secondhand smoke, in which many have been determined to be related to cancer, according to the The American Pregnancy Association.

In a 2014 study, published in Tobacco Control, researchers investigated the effects of secondhand smoke using quantified, lifetime exposure levels. They found pregnant women exposed to high levels of secondhand smoke had a higher rate of miscarriages, stillbirths, and fetal deaths. They concluded the pregnancy risks associated with women's secondhand smoke exposure were almost as high as the risks related to their own cigarette smoking.

Secondhand smoking can directly affect a fetus even before a woman becomes pregnant. Slotkin and his colleagues saw the smoke damaged areas of the brain involved in learning, memory, and emotional responses, in the new study published in Toxicological Sciences . Although the most severe impacts occurred during late gestation, the negative effects of secondhand smoke on the fetuses' brain development happened even when mothers were only exposed before conception.

Woman with cigarette in hand Women exposed to secondhand smoke risk poor fetal brain development, even before conception. Photo courtesy of Pexels, Public Domain

It's not yet known how smoke exposure damages fetal brain development prior to pregnancy. The researchers do suspect the lingering effects of smoke of the smoke components can remain in the body for several days after exposure. They also hypothesized that the chemicals might change the mother's metabolism or hormonal status, or the chemical could be causing an epigenetic alteration in the egg, affecting the gene activity that control brain function.

"Our study clearly shows there is no stage in which tobacco smoke is innocuous to the developing fetus," said Slotkin.

Slotkin and his colleagues simulated secondhand smoke exposure by capturing and extracting the chemical compounds of tobacco smoke, and administering the solution through pumps in the lab with groups of female rats. They received the tobacco smoke extract during one of the three periods: prior to mating, early gestation or late gestation. Offspring was studied starting in early adolescence and into adulthood, with a focus on brain regions known to be negatively affected by nicotine and tobacco smoke.

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The tobacco smoke extract in all three periods led the offspring to experience impaired function of the cholinergic brain circuits that govern learning and memory, and of the serotonin circuits that affect mood and emotion behavior, according to the researchers.

They emphasize the public health implications of secondhand smoke should be obvious to ll.

Bottomline: Exposure to secondhand smoke is especially dangerous to women of childbearing age, and the future fetus, even before pregnancy begins.

Sources: Slotkin TA, Stadler A, Skavicus S et al. Is There a Critical Period for the Developmental Neurotoxicity of Low-Level Tobacco Smoke Exposure? Toxicological Sciences. 2017.

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