Common Maternal Infections During Pregnancy: New Research Offers Reassurance
Extensive research, drawing upon nationwide data from Denmark, suggests that routine infections experienced by expectant mothers are unlikely to significantly impact their children’s cognitive abilities later in life. This comprehensive study, one of the largest of its kind, analysed the academic performance and intelligence quotient (IQ) scores of over 250,000 siblings. The findings revealed no consistent differences based on whether their mothers had been prescribed antibiotics or required hospitalisation for an infection during pregnancy.
While certain severe infections during pregnancy, such as rubella or toxoplasmosis, are known to present risks to the developing foetal brain, the wider implications of more common infections – for instance, urinary tract infections or respiratory illnesses – have remained less clear. Previous research had hinted at a potential influence of these everyday ailments on a child’s future cognitive performance. However, many of these earlier investigations struggled to fully account for shared family characteristics that could skew the results, such as parental intelligence, socioeconomic background, or inherited predispositions.
Addressing Previous Research Limitations
According to researchers, previous studies and anecdotal clinical observations have suggested a negative impact of common maternal infections on offspring cognitive outcomes. However, most prior studies were limited by their size and an inability to adequately adjust for the social factors associated with both the risk of maternal infection during pregnancy and the cognitive development of the offspring.
By leveraging data from a previous study on gestational age at birth and long-term cognitive outcomes, researchers were able to investigate the link between common maternal infections during pregnancy and long-term cognitive outcomes within a very large, nationwide cohort of full siblings. This sibling-based approach allowed researchers to compare siblings born to the same mother, with one experiencing an infection during pregnancy and the other not, thereby minimising the influence of confounding social factors.
Data and Methodology
The research data was sourced from multiple national Danish registries. Information was gathered on prescriptions for antimicrobial medications, serving as an indicator of mild infections, and inpatient hospital admissions, representing more severe cases. These records were then linked to standardised school grades in language and mathematics at ages 15-16, as well as intelligence test scores from mandatory military conscription assessments taken by adolescent boys.
The study cohort comprised over 274,000 children born between 1996 and 2003. Of these, nearly 81,000 had mothers who had filled at least one prescription for a systemic antimicrobial during pregnancy. A smaller group – approximately 5,600 children – had mothers who were hospitalised for infections during pregnancy. Intelligence scores were available for a subset of full brothers who had undergone testing for military service.
Key Findings: No Significant Impact on Cognitive Outcomes
The results indicated minimal to no difference in academic or cognitive performance based on maternal infection exposure. For example, among children whose mothers filled one prescription for antibiotics during pregnancy, the average difference in language or maths grades was negligible once shared family factors were considered. Similarly, the estimated IQ difference in adolescent males was only about 0.3 points on average – well within the margin of error.
Interestingly, when the researchers examined models that did not account for shared family factors, they found consistent and statistically significant associations between maternal infections and lower scores. This discrepancy underscores the potential for family-level confounding to influence results and highlights the importance of sibling-based analyses in mitigating such biases.
Specific Infections and Timing of Exposure
Even when analysing different types of antibiotics or the timing of exposure across pregnancy, the results revealed no consistent effects. The most commonly prescribed antibiotics – such as beta-lactams – showed no meaningful associations with lower academic performance or IQ. Furthermore, the timing of exposure appeared to be inconsequential: infections occurring during early gestation, late gestation, or any specific two-week period were not linked to poorer outcomes.
While there were a few minor exceptions, such as a slight reduction in mathematics scores among children whose mothers had filled one or two antibiotic prescriptions, these differences were minimal and deemed unlikely to be meaningful at the individual or population level.
The study also investigated whether more severe infections, indicated by hospitalisation, might have a stronger effect. One notable finding was a slight dip in school grades among children whose mothers had been hospitalised for an infection during weeks 24-25 of pregnancy. However, this effect disappeared when the analysis was restricted to children born at full term, suggesting that the initial association may have been influenced by gestational age rather than the infection itself.
Robustness of Findings
The researchers conducted several sensitivity analyses to assess the robustness of their findings. These included restricting the sample to term births, adjusting for maternal smoking, and imputing scores for children who did not participate in school exams. Across these variations, the results remained consistent: there was no evidence of significant cognitive harm associated with common infections during pregnancy.
Implications and Limitations
The study suggests that common maternal infections and the associated antimicrobial treatment during pregnancy are unlikely to significantly impair offspring cognitive outcomes, such as school grades or adolescent IQ. This offers reassuring evidence supporting the safety of commonly prescribed antimicrobials during gestation and suggests a minor role of common prenatal infections in cognitive deficits in offspring.
However, the study does have limitations. It lacked information on medications administered during hospital stays, which could potentially affect outcomes. Another limitation is that the researchers could not identify specific pathogens responsible for infections, nor could they account for maternal fever, which is often part of the body’s inflammatory response.
Future studies could potentially explore specific infections, an aspect that was not possible in the current study, which only identified infections through antibiotic prescriptions and diagnostic codes for infectious disease hospitalisations.
Cautions and Broader Methodological Implications
While the findings apply to common infections and antibiotic use, they do not negate the well-established effects of rare but serious prenatal infections. Such conditions can still cause significant developmental disabilities, and preventative measures remain crucial for managing those risks. The findings are mainly applicable to common maternal infections identified by maternal antibiotic prescriptions and common hospitalisations for infections, as it was where most statistical power to indicate a difference existed.
The research also carries broader methodological implications. The study highlights the potential for family-level confounding to play a larger role than previously appreciated in shaping observed outcomes. Earlier studies had suggested negative outcomes associated with prenatal infection, but these associations often vanished when sibling comparisons were employed. This underscores the importance of using study designs that can effectively address the impact of social biases.