The study aimed to evaluate the association between maternal infection during pregnancy and childhood leukaemia among offspring. The researchers used data from 7 Danish national registries. The study included more than 2.2 million children. The results showed that children born to mothers with infections during pregnancy had a 35% increased risk of leukaemia compared with children born to mothers without infections. Maternal genital and urinary tract infections were associated with a 142% and 65% increased risk of childhood leukaemia, respectively.

This large population-based cohort study adds to the growing body of evidence suggesting that maternal infection during pregnancy may be associated with an increased risk of childhood leukaemia. The use of national registries and the validation of findings in a separate cohort strengthen the study's validity. The adjustment for potential confounders and the sibling analysis to account for unmeasured familial confounding also increase the study's reliability.

The study's findings have important implications for understanding the aetiology of childhood leukaemia and developing preventive measures. However, several limitations must be considered. Firstly, the study relied on registry data, which may not have captured all relevant information, such as specific types of infections or the severity of the infections. Secondly, the study did not differentiate between bacterial and viral infections, which may have different effects on foetal development. Thirdly, the study did not investigate potential mechanisms underlying the association between maternal infection and childhood leukaemia. It must also be pointed out that childhood leukaemia, the most common childhood cancer, is a rare condition. The increase in risk, while statistically significant, translates into only a very small increase in the number of children who may develop the disease.

The study by Dr He and colleagues suggests children born to mothers who had certain maternal infections during pregnancy had a higher chance of developing leukaemia than those born to mothers who did not have an infection. However, the absolute risk of developing leukaemia was small since it is a rare condition. Childhood leukaemia, which is the most common childhood cancer, affects around 250 Australian children a year.
 
This was a well conducted study using data from Denmark, which is well known for its high-quality population- level health information. The findings of this study add to what it known about the origins of the disease. As leukaemia mainly occurs in children aged under five years, it is thought that it may be triggered by events before birth or in early life.

While exciting, the findings of this study need to be verified by research in other populations and about possible mechanisms.