A large U.S. cohort study reveals how smoking during pregnancy affects children’s mental health, increasing overall symptom burden while potentially leading to externalizing patterns of behavior from childhood to adolescence.
Study: Association between prenatal smoking and child psychopathology by age and gender in the ECHO cohort. Image credit: Bernardo Emanuelle/Shutterstock.com
Research published in Development and psychopathology We investigate how maternal smoking during pregnancy (MSDP) relates to children’s mental health, focusing on both overall symptom severity and the balance of internalizing and externalizing problems across development.
MSDP and mental health
Mothers share common genetic and environmental influences with their offspring. This explains some of the externalizing symptoms associated with MSDP. However, internalizing and externalizing symptoms are often highly correlated, especially in adolescence.
MSDP may not be specifically associated with externalizing symptoms. Rather, MSDP may predispose to mental illness or contribute to both externalizing and internalizing symptoms. Single sibling studies suggest that externalizing symptoms are more common in MSDP.
Externalizing and internalizing symptoms
Externalizing and internalizing symptoms refer to manifestations of mental ill health. The former includes outward behaviors such as aggression, hyperactivity, and rule-breaking. Internalizing behaviors are behaviors that are turned inward, such as anxiety, depression, and social withdrawal.
These types of symptoms appear at different ages. Externalizing symptoms tend to appear early and are more common in boys. Internalizing symptoms are more common during adolescence and affect more girls than boys. However, no consistent developmental pattern has been observed between either type or gender.
Furthermore, studies suggest that boys are more likely to be negatively affected by MSDP throughout their development. MSDP is also associated with higher levels of externalizing behavior within the same child over time. This motivated the authors to look for development windows that are sensitive to MSDP.
Disentangling mental health symptoms associated with MSDP
To better understand how prenatal smoking is associated with different types of mental health problems, researchers applied the severity-direction model of psychopathology, a framework designed to separate overall symptom burden from the balance of symptom types.
In this model, severity reflects the total level of psychopathology across both internalizing and externalizing domains and captures the extent of comorbidity, as higher severity scores typically indicate the simultaneous presence of both types of symptoms. In contrast, orientation captures the relative predominance of one symptom type over another and indicates whether an individual’s profile leans toward internalizing problems, such as anxiety and depression, or toward externalizing behaviors, such as aggression and hyperactivity, regardless of total symptom load.
This approach allows researchers to go beyond traditional analyzes that examine internalizing and externalizing symptoms separately to more accurately assess whether MSDP is associated with general mental health risks, domain-specific effects, or both.
MSDP predicts more severe symptoms
The study involved 16,335 children, mostly white, between the ages of 1 and 18. These were collated from 55 cohorts within the Environmental Impact on Child Health (ECHO) consortium. Although the majority of participants were Caucasian, the sample was sociodemographically diverse.
Across all age groups examined at 2-year intervals, maternal smoking during pregnancy was consistently associated with increased overall symptom severity, indicating a greater co-morbid burden on the mental health of exposed children. Importantly, these associations remained statistically significant even after adjusting for a wide range of potential confounders, including sociodemographic factors, family psychiatric history, other prenatal drug use, and postnatal smoking exposure.
When examining gender differences, the results were similar for boys and girls. One exception appeared in the 13- to 14-year age group, where the association with symptom severity appeared stronger in boys, but this pattern was not observed in other age groups and should be interpreted with caution, especially given the variation in sample size.
There is no difference in age or gender
Overall, this finding showed consistency across developmental stages, with similar patterns of association observed from infancy to adolescence. Although this study was designed to detect potential age- or gender-specific effects, there was little evidence of strong or systematic differences between age groups or between boys and girls.
Although certain analyzes suggested possible variation, such as slightly stronger effects in childhood and early adolescence, these patterns were not robust and often attenuated when additional covariates were included or sample size was reduced. As a result, the results of this study do not provide strong evidence for a well-defined sensitive developmental period during which MSDP exerts uniquely enhanced effects.
Rather, the results suggest that the effects of prenatal smoking on mental health may be: This reinforces the importance of prevention efforts aimed at reducing maternal smoking during pregnancy, rather than targeting a specific postnatal intervention period.
strengths and limitations
This study has several limitations, including the lack of self-reported MSDP data and data on the timing and frequency of prenatal smoking. The psychopathology scoring system used here does not demonstrate measurement invariance across age groups, limiting direct comparisons across age and gender categories.
Again, symptom severity is more strongly associated with the transmission of psychopathology across generations than with the actual type of symptoms (externalizing vs. internalizing). Therefore, this study may have overestimated the risk of symptom severity from MSDP alone, as it did not incorporate risks due to life stress or genetic factors, suggesting that the results should not be interpreted as strictly causal.
Still, this study used a large, sociodemographically diverse sample, which increases generalizability and allows detection of small associations.
what it means
These findings suggest that MSDP is associated with increased severity of multiple types of mental health symptoms in offspring.
It also shows that problems are more likely to manifest across multiple developmental periods rather than a single age group. However, sample sizes for other age categories were much smaller, suggesting that although some patterns may suggest differences across developmental stages, there is no strong or consistent evidence for distinct MSDP-susceptible periods. Rather, it is important to suppress MSDP and prevent prenatal exposure.
Furthermore, interventions should be broadly targeted to at-risk children into adulthood, rather than being applied during critical periods.
The occurrence of internalizing symptoms may primarily reflect a higher risk of comorbidity with MSDP, whereas externalizing problems may reflect both general severity and some domain-specific risk. “This indicates that there are multiple pathways from MSDP to psychopathological symptoms in childhood and adolescence.”
This paper provides a new perspective on pediatric neurodevelopment while suggesting the importance of reducing MSDP to minimize the risks associated with mental health disorders in children.
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