Researchers from the Center for Data and Knowledge Integration for Health (Cidacs/Fiocruz Bahia) conducted a study that analyzed more than 6.9 million live births in the country.

Arboviruses, diseases transmitted by the Aedes aegypti mosquito, such as dengue, Zika, and chikungunya, represent a growing concern for maternal and child health in Brazil. Selected as one of the 50 best articles recently published on public health in the journal Nature Communications, a study by Fiocruz analyzed more than 6.9 million live births in the country between 2015 and 2020 and revealed that infection with these viruses during pregnancy is associated with higher risks of complications during childbirth and for newborns, including premature birth, low birth weight, and even neonatal death.

The findings of the research, conducted by scientists from the Center for Data and Knowledge Integration for Health (Cidacs/Fiocruz Bahia), indicated that arbovirus infection during pregnancy increased the risk of premature birth, low Apgar score (a rapid assessment performed after birth to verify adaptation to life outside the womb), and neonatal death.

Regarding diseases, dengue fever, in addition to being linked to premature birth and low birth weight, has also shown an association with structural and functional alterations in fetal development, known as congenital anomalies. In the case of Zika, the adverse effects were even more extensive, especially congenital malformations, the risk of which was more than doubled among babies of infected mothers.

Research leader Thiago Cerqueira-Silva points out, however, that risk patterns vary depending on the virus and the period of infection. "The study provides robust and detailed evidence that debunks the idea that only Zika is a major threat during pregnancy." We have shown that chikungunya and dengue also have serious consequences, such as an increased risk of neonatal death and congenital anomalies. This information is crucial for directing clinical and public health attention,” he explains.

The researcher also points out that the study provides new evidence on the impacts of arbovirus infections during pregnancy, indicating periods of greater vulnerability in each trimester. The variation in risk suggests that different biological mechanisms are at play in each phase, which reinforces the importance of surveillance and prevention throughout pregnancy.

Complications during childbirth "Our study defines the 'critical windows' of vulnerability, showing in which quarter each infection presents the greatest risk." This allows healthcare professionals to better guide

pregnant women and intensify monitoring during periods of greatest risk. Finally, considering climate change, the study is relevant for regions beyond the tropics,” Thiago notes.

What motivated the group to focus on this topic was the limited number of studies investigating the clinical consequences of arbovirus infection during pregnancy, as well as the existence of conflicting conclusions in the scientific literature.

“Previous studies were mostly based on small cohorts, which limited the ability to accurately assess multiple outcomes. Furthermore, many contained significant methodological flaws, such as the ‘immortal time bias,’ which occurs when infection is not treated as an event that happens at a specific point during gestation, potentially underestimating the true risks. Our goal was to overcome these limitations,” the researcher emphasizes.

“By analyzing the infection as a time-varying event, we obtained more accurate risk estimates. If we had used the traditional approach (disregarding when the infection occurs), the risks of premature birth and low birth weight would have been underestimated or even masked. This shows that how we analyze the data is as important as the data itself,” he concludes.

The research used data from the Cidacs/Fiocruz Bahia Cohort of 100 million Brazilians and, to reinforce the consistency of the results, the researchers applied a "negative control": they analyzed arbovirus infections that occurred between 6 and 24 months before pregnancy. In this analysis, the effects of infections prior to pregnancies were minimal or nonexistent, reinforcing that the study's findings are robust.