A large US cohort study shows how smoking during pregnancy may affect children’s mental health, increasing overall symptom burden while pushing toward externalizing patterns of behavior in childhood and adolescence.
Study: Association of prenatal smoking and child psychopathology by age and sex in the ECHO cohort.. Image Credit: Bernardo Emanuel/Shutterstock.com
A study published in development and psychopathology Investigates how maternal smoking during pregnancy (MSDP) is related to children’s mental health, focusing on both overall symptom severity and the balance between internalizing and externalizing problems during development.
MSDP and mental health
Mothers share common genetic and environmental influences with their offspring. This explains to some extent the external symptoms associated with MSDP. However, internalizing and externalizing symptoms are often highly correlated, especially in adolescence.
MSDP may not be specifically associated with external symptoms; Rather, MSDP may cause mental ill health, or contribute to both externalizing and internalizing symptoms. A single sibling study suggests that externalizing symptoms are more common with MSDP.
externalizing vs internalizing symptoms
External and internal symptoms reflect manifestations of mental illness. The former includes externally directed behaviors such as aggression, hyperactivity, and rule-breaking. Internalizing behaviors are introverted, such as anxiety, depression, or social isolation.
These symptom types appear at different ages. External symptoms appear earlier and occur more frequently in boys. Internalizing symptoms usually appear more in adolescence and affect girls more than boys. However, no consistent developmental pattern has been observed for any type or all sexes.
Additionally, several studies suggest that male fetuses are more likely to have adverse effects of MSDP throughout development. MSDP is also associated with higher externalizing behavior within the same child over time. This prompted the authors to search for an MSDP-sensitive developmental window.
Resolving mental health symptoms associated with MSDP
To better understand how prenatal smoking is related to a variety of mental health problems, researchers applied the severity-directionality model of psychopathology, a framework designed to disentangle overall symptom burden from the balance of symptom types.
In this model, severity reflects the total level of psychosis in both internalizing and externalizing domains, capturing the extent of comorbidity, as higher severity scores generally indicate the simultaneous presence of both types of symptoms. In contrast, directionality captures the relative predominance of one trait type over another, indicating whether an individual’s profile leans more toward internalizing problems, such as anxiety or depression, or toward externalizing behavior, such as aggression or hyperactivity, regardless of total trait load.
This approach allows researchers to move beyond traditional analyzes that examine internalizing and externalizing symptoms separately, making it possible to more accurately assess whether MSDP is associated with general mental health risk, domain-specific effects, or both.
MSDP predicts more severe symptoms
The study included 16,335 children aged 1–18, who were mostly white. These were collected from 55 groups within the Environmental Effects on Child Health Outcomes (ECHO) consortium. The sample was socio-demographically diverse, although the majority of participants were White.
Across all age groups examined over a two-year period, maternal smoking during pregnancy was consistently associated with higher overall symptom severity, indicating greater concomitant mental health burden among exposed children. Importantly, these associations remained statistically significant even after adjustment for a wide range of potential confounders, including sociodemographic factors, family psychiatric history, other prenatal substance use, and postpartum smoking exposure.
When examining gender differences, the findings were largely similar for boys and girls. An exception emerged in the 13–14 year age group, where the association with symptom severity appeared stronger in boys, although this pattern was not seen in other age groups and should therefore be interpreted with caution, especially given the variability in sample size.
no age or gender difference
Overall, the findings showed consistency across developmental stages, with similar patterns of engagement observed from early childhood through adolescence. While the study was designed to explore potential age- or gender-specific effects, there was little evidence of strong or systematic differences across age groups or between boys and girls.
Although some analyzes indicated potential variation, such as slightly stronger effects in early childhood or early adolescence, these patterns were not robust and were often attenuated when additional covariates were included or when the sample size was reduced. As a result, the findings do not provide strong evidence for clearly defined sensitive developmental periods during which MSDP exerts a uniquely enhancing effect.
Instead, the results suggest that prenatal smoking may have an impact on mental health. Widely distributed throughout development, reinforcing the importance of prevention efforts aimed at reducing maternal smoking during pregnancy rather than targeting specific postpartum intervention windows.
Strengths and limitations
The study has some limitations, such as self-reported MSDP data and lack of data on timing and frequency of smoking in the prenatal period. The psychopathology scoring system used here could not be confirmed as measurement-invariant across age groups, limiting direct comparisons across age and gender categories.
Again, symptom severity is more strongly linked to the transmission of psychosis between generations rather than the actual type of symptom: externalizing versus internalizing. Thus, this study may have underestimated the risk of symptom severity from MSDP alone by not including risk due to life stress and genetic factors, suggesting that the findings should not be interpreted strictly as causal.
Nevertheless, this study used a large, socio-demographically diverse sample, improving its generalizability and allowing the detection of smaller associations.
intent
These findings suggest that MSDP is associated with increased severity of a variety of mental health symptoms in offspring.
They also indicate a greater tendency to externalize problems across multiple developmental periods rather than within a single age group. However, there were much smaller sample sizes in other age categories, suggesting that although some patterns may indicate differences in developmental stages, there is no strong or consistent evidence for clear MSDP-sensitive periods. Rather, it is important to discourage MSDP and thus prevent prenatal exposure.
Furthermore, interventions should broadly target at-risk children until adulthood rather than being implemented at critical periods.
The occurrence of internalizing symptoms may primarily reflect higher risk of comorbidity with MSDP, whereas externalizing problems may reflect both general severity and, to a lesser extent, domain-specific risk. “This indicates that there are multiple pathways from MSDP to psychiatric symptoms in childhood and adolescence.”
Offering a new perspective on pediatric neurodevelopment, it suggests the importance of reducing MSDP to reduce the risk of related mental health disorders in children.
