On Nov. 15, 2024, a team led by researchers from Sweden’s Karolinska Institutet reported study results that showed exposure to tetracycline antibiotics during the first trimester of pregnancy is not tied to increased risks of major congenital malformations (MCMs). The study was published in JAMA Network Open.

The findings were from a population-based cohort study that used data from Swedish health and population registries on children born from July 1, 2006, to December 31, 2018. The study compared MCMs—such as heart defects, cleft lip, cleft palate, and neural tube defects—among children who were exposed to tetracyclines during the first trimester and those who weren’t.

Analysis of secondary outcomes found no increased risk in 10 of 12 major malformation organ system subgroups and none of 16 individual malformations. An observed higher risk for nervous system anomalies and eye anomalies did not hold up in a sensitivity analysis with follow-up extended to age 3 years.