Experiencing severe respiratory infections during the first trimester of pregnancy triples the risk of some cardiovascular defects at birth, a UNSW Sydney study has found. 

The findings have prompted UNSW researchers to recommend women take precautions against contracting respiratory infection during pregnancy including influenza vaccination, not smoking or undergoing x-rays where possible.

“There is limited evidence around this issue, but our study supports that there is an association between severe respiratory infections during pregnancy and selected cardiovascular anomalies in babies,” said lead author Dr Abrar Chughtai, from UNSW Medicine & Health.

In previous studies, the link between respiratory infections and congenital anomalies has been difficult to prove. The studies often involved asking new mothers, whose babies were healthy or had congenital issues, whether they had experienced a respiratory infection when pregnant.

In this research, the researchers analysed data from almost 1.5 million births in NSW from 2001-2016, linking health records for mothers and babies. The health data included hospital admissions during pregnancy for severe respiratory infections, births, and congenital issues.

Controlling for other factors like age, smoking and other illnesses, the researchers analysed the association between respiratory infections during pregnancy and various congenital abnormalities.

The researchers found that there was a link between severe respiratory infections and some types of cardiovascular abnormalities. For the 1,547 mothers who were hospitalised for respiratory infections during the first trimester of pregnancy, seven (0.45%) had babies with these heart and circulation issues. Whereas for the other 1,441,327 mothers in the study, 1,724 (0.12%) had babies with these cardiovascular abnormalities.

“After controlling for other factors, still respiratory infections were associated with selected cardiovascular defects,” Dr Chughtai said.

“The risk is three times higher if the mother had an infection during the first trimester of pregnancy.”

Rates of selected major cardiovascular anomalies were also higher in babies if the mother had influenza during the first trimester of pregnancy, but this was not statistically significant.

Respiratory infections may harm foetal development

The researchers hypothesise several reasons for a link between respiratory infections early in pregnancy and cardiac defects.

“For example, some infectious diseases may pass directly to the baby across the placenta, leading to problems in development,” Dr Chughtai said.

“Another reason is use of medications. The mother may need to take antibiotics or some other drugs to treat infections. These may indirectly affect the baby.”

“Moreover, if the mother has a fever due to infection, there are metabolic changes in the body, and these metabolites may cross the placenta which may affect the baby. High fever may also impair protein synthesis and causes cell death, resulting in congenital anomalies.”

The impacts of COVID-19 were not analysed, which emerged after the study period of 2001-2016. The researchers plan to investigate in a follow-up study.

“So far from other studies there is no evidence that COVID-19 increases the risk of congenital abnormalities. But this is only initial research,” Dr Chughtai said.

Implications for pregnancy

The researchers recommend avoiding respiratory infections during pregnancy as much as possible, to protect against congenital abnormalities.

“There are well-established risk factors, for example, x-rays and smoking, but infection is also a risk.

“One of the important methods of prevention is influenza vaccination, which is available and effective and very safe in pregnant women,” Dr Chughtai said.

The research is published in published in BMC Pregnancy and Childbirth.