Refusal of prophylactic vitamin K in newborns is increasing, and infants who do not receive vitamin K have a significantly elevated risk of bleeding during their first 6 months, according to a US cohort study.
Between 2017 and 2025, the proportion of newborns not receiving vitamin K increased from 3.1 percent to 6.8 percent (p<0.001). Similarly, the number of infants with bleeding increased across the study period, from 225.3 to 394 per 10,000 births among those who did not receive vitamin K and from 136.6 to 221.8 per 10,000 births among those who did receive vitamin K. [JAMA 2026;doi:10.1001/jama.2026.21764]
Compared with infants who received vitamin K, those who did not had significantly higher risk of bleeding within the first 6 months of life (288 vs 185.9 per 10,000; adjusted risk ratio [aRR], 1.47, 95 percent confidence interval [CI], 1.43–1.51).
Infants who did not receive vitamin K also had more than twofold higher risks of intracranial bleeding (33 vs 13.2 per 10,000; aRR, 2.43, 95 percent CI, 2.26–2.62) and mortality with concurrent bleeding during the birth hospitalization (2.9 vs 1.1 per 10,000; aRR, 2.69, 95 percent CI, 2.09–3.47).
The retrospective cohort study included 5,240,780 infants born at 35–43 weeks of gestation between 2017 and 2025 at hospitals and health systems across 50 states in the US. Of these infants, 234,825 (4.5 percent) did not receive vitamin K and 99,828 (1.9 percent) had infant bleeding.
Compared with infants who did receive vitamin K, those who did not had a higher mean gestational age (38.8 vs 38.6 weeks) and were more likely to be non-Hispanic White (60.1 percent vs 51.6 percent) and born to nulliparous individuals (45.1 percent vs 37.6 percent).
Bleeding within 6 months of birth was associated with male sex, lower gestational age, higher birth weight, non-Hispanic Native Hawaiian or Other Pacific Islander and non-Hispanic White race and ethnicity, private insurance, and the least social vulnerability.
“This study gives parents, paediatricians, nurses, and other healthcare professionals a foothold in the evidence by providing contemporary US data about the increased risk of bleeding associated with the declination of vitamin K,” wrote Dr Laura Kair from the University of California Davis School of Medicine, Sacramento, California, US, and colleagues in an accompanying editorial. [JAMA 2026;doi:10.1001/jama.2026.23146]
“As with all serious but rare outcomes, vitamin K deficiency bleeding risk is a difficult concept to communicate, and when presented as a percentage may seem purely theoretical,” Kair and colleagues continued.
“Based on the authors’ calculation of number needed to harm, one additional infant would have a bleeding event if just 114 infants did not receive vitamin K. This number needed to harm provides a powerful narrative that may be more readily accessible to parents, supporting more effective counselling and decision-making,” they said.
Kair and colleagues emphasized that paediatric clinicians could use the data presented in the study to communicate that intramuscular vitamin K prophylaxis confers protection against bleeding, helping prevent the moment when a parent reports, “If only I had known the risk.”