Study of 2 million newborns links skipping vitamin K injection at birth to higher bleeding risk

A large Swedish study involving more than 2 million newborns has found that infants who did not receive the routine vitamin K injection after birth were significantly more likely to experience serious bleeding during their first six months of life, including life-threatening bleeding in the brain.

The study, published in JAMA Pediatrics, analyzed health records of babies born in Sweden between 2003 and 2021 at 35 weeks' gestation or later. Researchers examined vitamin K prophylaxis at birth and tracked bleeding-related diagnoses during the first six months of life.

Although refusal of the vitamin K injection remained uncommon, the proportion of newborns who did not receive it more than doubled during the study period, increasing from 0.66% in 2006 to 1.50% in 2021.

Among more than 2 million infants included in the analysis, 24,089 did not receive the standard intramuscular vitamin K injection. These babies had approximately 1.5 times higher odds of being diagnosed with any type of bleeding during the first six months of life and were nearly three times more likely to develop intracranial hemorrhage than infants who received the injection.

Vitamin K is essential for activating clotting proteins that help stop bleeding. Newborns naturally have very low vitamin K levels because only small amounts are transferred during pregnancy, breast milk contains little vitamin K, and their intestinal bacteria have not yet matured enough to produce it.

When parents decline the injection or when infants have certain medical conditions, oral vitamin K drops may be used instead. However, the study found that babies who received oral vitamin K still had more than twice the risk of bleeding compared with those given the injection. The researchers suggest this may be because oral supplementation requires repeated doses over several weeks, increasing the likelihood of missed or inconsistent treatment.

The highest risk of intracranial bleeding was observed during the first 28 days after birth.

According to the researchers, the findings add to growing evidence supporting routine vitamin K injections for newborns and highlight the need to improve parental education about their benefits. They also call for further research into the reasons some parents decline vitamin K prophylaxis and whether this decision is associated with other health-related choices, including childhood vaccination.