Cigarette smoking during pregnancy linked to ADHD risk in offspring

(Reuters Health) - Children born to women who smoke cigarettes during pregnancy, especially when mothers are heavy smokers, are at an increased risk for attention-deficit/hyperactivity disorder (ADHD), a new review of medical studies confirms.

Mothers who smoked during pregnancy had an overall 60 percent higher risk of having a child with ADHD compared to women who didn’t smoke. For mothers who smoked fewer than 10 cigarettes per day, the risk of having a child who developed ADHD was 54 percent higher than for nonsmoking mothers. For mothers who were heavier smokers, the risk was 75 percent higher than for nonsmokers.

An increased risk of ADHD for children of women who smoke while pregnant has been reported before. What’s new here, the authors say, is that the data have been pooled from studies in multiple countries and time periods, and also that as the daily tally of cigarettes went up, the risk of ADHD went up.

The findings “lend greater strength and credibility and statistical power to previous studies that likewise show that pregnant women who smoke have a greater likelihood of having a child with ADHD,” said Dr. Andrew Adesman, chief, developmental and behavioral pediatrics, Steven and Alexandra Cohen Children’s Medical Center of New York in New Hyde Park.

Adesman, who was not involved in the research, told Reuters Health by phone that the study ”has to be taken seriously. Women who smoke during pregnancy have one more reason to stop.”

According to 2011 Pregnancy Risk Assessment and Monitoring System (PRAMS) data from 24 states, approximately 10 percent of American women reported smoking during the last three months of pregnancy.

Eleven percent of U.S. children ages 4 to 17, or 6.4 million children, have been diagnosed with ADHD based on parent reports, according to the Centers for Disease Control and Prevention. ADHD can affect attention, hyperactivity and self-control, causing difficulty in school and socially.

As reported in Pediatrics, Dr. Dezhi Mu and colleagues at West China Second University Hospital in Chengdu, Sichuan, China, analyzed 20 studies published between 1998 and 2017 that looked at the potential role of smoking during pregnancy and the risk of ADHD in offspring. Altogether, the studies involved nearly 3 million people in Europe, Brazil, Japan, Australia and the U.S.

The team found lower risks for ADHD in children of mothers who smoked in the U.S. and Europe, where more smokers stop smoking when they get pregnant.

“It would be a big leap from that, but if you are a prior smoker and stop during pregnancy, the inference is that the risk of ADHD goes down,” Dr. Jeffrey Newcorn, director, The Center of Excellence in ADHD and Related Disorders, Icahn School of Medicine at Mount Sinai told Reuters Health in a phone interview.

Data from seven studies showed that while mothers’ smoking had a greater effect than fathers’ smoking on ADHD risk, there was still a 20 percent higher risk of ADHD in children born to fathers who smoked.

The new analysis can’t prove that smoking causes ADHD. Among other limitations of the new research are that different criteria were used to diagnose ADHD in the various studies, and tobacco use during pregnancy was self-reported by the mothers.

Newcorn, who was not involved in the research, would like to see more studies on the relationship between genetic and environmental factors in developing ADHD, as well as the role of nicotine exposure.