A new 2025 study from the Japan Environment and Children’s Study (JECS) takes a closer look at how smoking during pregnancy affects young children’s development. While we often hear that smoking can lead to lower birth weight or exposure to harmful chemicals, this research wanted to understand something deeper: does smoking itself directly influence how a child grows, learns, and develops in the first few years of life? To answer this, the researchers followed nearly 4,800 mother–child pairs, tracking the mothers’ smoking habits and evaluating the children’s developmental skills at ages two and four.
The mothers in the study were grouped by their smoking behavior: those who never smoked during pregnancy, those who quit before pregnancy, those who quit after finding out they were pregnant, and those who continued smoking throughout. The children were later assessed on thinking skills, early language and communication, social behavior, and motor skills. The researchers also looked at factors like birth weight and cadmium levels in the mother’s blood, since cadmium is a toxic metal found in cigarette smoke and has been linked to developmental concerns.
The clearest finding was that boys whose mothers smoked while pregnant showed noticeable developmental delays at both ages two and four. Their scores in areas like problem-solving, communication, and social development tended to be lower compared to boys whose mothers did not smoke. Interestingly, the same pattern was not as strong or consistent in girls, suggesting that boys may be more sensitive to prenatal exposure to smoking. The study also showed that the developmental differences were not simply due to babies being born smaller or being exposed to cadmium—meaning the act of smoking itself likely plays a direct role in affecting early brain development.
For families and health professionals, these findings offer an important takeaway. Avoiding smoking during pregnancy is not only about protecting a baby’s physical health at birth—it also supports the child’s long-term developmental well-being. This research adds another layer to our understanding of prenatal health and reinforces why reducing smoking during pregnancy remains a critical public health priority.
If you want to read more, click here!
Erin Mulroy
UConn Kids Research Assistant