Fetuses whose mothers had COVID-19 or were vaccinated during the first three months of pregnancy are not at increased risk of birth defects. This is the result of a large Nordic study published in the British Medical Journal.
In a collaboration between the Norwegian Institute of Public Health, the University of Copenhagen and Karolinska Institutet, researchers conducted a large Nordic registry study to investigate the risk of major birth defects after COVID-19 infection or vaccination with mRNA vaccine during the first trimester.
They looked at 11 different groups of major birth defects and found no increased risk for any of them.
This is the first comprehensive study on birth defects linked to infection or vaccination that has been possible to conduct as there has only now been sufficient follow-up time to capture both exposure in the first trimester and birth defects that can be detected in the first year of life.
Collaboration between several countries was also necessary to have a large enough study population and good registry data.
"Our study found that it was safe to be vaccinated with mRNA vaccines against COVID-19 during pregnancy. This is important as Covid-19 infection may lead to adverse pregnancy outcomes in both mother and child", says Olof Stephansson, Professor in Clinical Epidemiology at the Deparment of Medicine, Solna, Karolinska Institutet.
More about the study
The study included a total of 343 066 live births, of which 161 284 were in Sweden, 103 747 in Norway and 78 035 in Denmark. The pregnancies were between March 1, 2020, and February 14, 2022.
In total, 516 out of 10,000 babies had a major malformation according to the EUROCAT definitions and these were detected before 9 months of age. 3% of the babies had mothers who had a Covid-19 infection in the first trimester, while 19% had mothers who were vaccinated in the first trimester.
In those exposed to COVID-19 infection in the first trimester, the incidence of major birth defects was 483 per 10 000, compared to 517 per 10 000 among the unexposed.
In those vaccinated in the first trimester, the incidence of major malformations was 478 per 10 000 compared to 510 per 10 000 among the unexposed.
There were no differences in risk with different COVID-19 virus variants or different vaccine types. The researchers were only able to study the mRNA vaccines from Pfizer and Moderna as these two have been recommended for pregnant women in the three countries.
