Smoking during pregnancy gives a child smaller brains ten years later

Children of mothers who continue to smoke during pregnancy have measurably smaller brains by age 10. This is the conclusion of Erasmus MC researchers in a study published last week. The study emphasizes that smoking during pregnancy can have negative consequences for the child until long after birth.

“This provides new insights,” says Corine Verhoeven, professor of obstetrics at the University of Nottingham. “It is known that smoking during pregnancy poses a risk of long-term reduced health in children, but to my knowledge this is the first time that effects on brain development at this age have been demonstrated in this way.”

In 2021, eight percent of pregnant women in the Netherlands smoked at some point during their pregnancy, according to figures collected by the Trimbos Institute. 4.8 percent smoked during the entire pregnancy. That percentage has fluctuated around the same value for five years. Women with low income and low education continue to smoke more often during pregnancy than women with a higher socio-economic status.

Difficult to investigate

The risks of smoking for unborn and newborn children are often studied and widely known. For example, pregnant women who smoke have a higher risk of miscarriage or premature birth. Newborns of smoking mothers have a smaller head circumference and a lower birth weight at birth.

But the consequences of smoking during pregnancy later in the child’s life are more difficult to investigate. The Rotterdam brain size study is part of the Generation R study. It follows the development and health of growing children in Rotterdam over several years.

Researchers analyzed data from 2,704 women and their children. Participating women who were pregnant between 2002 and 2006 were asked if they smoked during their pregnancy. 364 women in this group (13.5 percent) continued to smoke during pregnancy. 238 women (8.8 percent) gave up as soon as they found out they were pregnant. With an MRI scan, the researchers determined brain size and structure in children when they were between 9 and 11 years old.

Children of mothers who smoked not only had a smaller total brain volume, but also less white matter (for signal transmission between brain cells) and gray matter (where most brain cells are located) and smaller deep convolutions (gyri) than mothers who never smoked or after smoking was discontinued in the first trimester. In this study, the Rotterdammers did not investigate whether children of smoking mothers also experienced cognitive disadvantages. “But in general, you can say that children with smaller brains have a lower IQ and more behavioral problems,” says Runyu Zou, epidemiologist and lead author of the paper.

Also read: babies easier at birth due to proximity to the chemical industry

The development of the brain

The researchers emphasize that there was no difference between children of mothers who never smoked and mothers who quit early in pregnancy. Only later in pregnancy does the growth and development of the brain really begin. “Even if a woman has smoked in the first 10 weeks of pregnancy, it still makes sense to quit,” says Zou.

“So young men and women would rather stop before they try to get pregnant,” says Corine Verhoeven. “It is precisely at the beginning of pregnancy that all the important organs are formed. In short, if you want to have children: stop smoking first, then use contraception.”

Do differences in brain size persist throughout life? “We can’t say that based on this research,” says Zou. “Perhaps differences will improve later in life. The brain is a plastic organ.” Zou and his colleagues plan to repeat the study when the Generation R participants are teenagers and young adults.

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