- Design
- nationwide register-linked cohort study with logistic regression, Sweden 2003–2021
- Population
- 2,020,302 live births at ≥35 weeks' gestation followed to 6 months; 24,089 with no record of intramuscular vitamin K
- Primary outcome
- bleeding diagnosis within the first 6 months of life
- Effect
- any bleeding adjusted OR 1.52 (95% CI 1.27–1.81); intracranial bleeding adjusted OR 2.91 (2.13–3.96); non-receipt rose from 0.66% in 2006 to 1.50% in 2021
Intramuscular vitamin K at birth prevents vitamin K deficiency bleeding, and refusal of it is rising internationally. This national cohort took every live birth in Sweden at 35 weeks or more between 2003 and 2021 — 2,020,302 infants — and followed them to six months through linked national registers.
The trend is the first finding. Non-receipt fell from 1.32% in 2003 to 0.66% in 2006, then climbed steadily and more than doubled, reaching 1.50% by 2021. That is 1,619 newborns in one year in one country with a well-functioning maternity system.
The outcome is the second. Infants without intramuscular vitamin K had adjusted odds of a bleeding diagnosis in the first six months of 1.52 (95% CI 1.27–1.81), and of an intracranial bleeding episode of 2.91 (2.13–3.96). Intracranial haemorrhage in a previously well infant is the presentation of late vitamin K deficiency bleeding, and it carries a high rate of death and permanent disability. This is a single injection, given once, with no serious adverse effect established in sixty years of use, and the conversation with parents who hesitate needs these numbers in it.
- Record vitamin K administration or refusal explicitly in the notes and in the child health record — this cohort found infants with no record at all.
- Where parents decline the injection, offer the oral schedule and be clear it requires three correctly timed doses and is less effective, particularly in cholestasis.
- Consider late vitamin K deficiency bleeding in any infant under six months with unexplained bruising, bleeding or an intracranial haemorrhage, and ask directly whether vitamin K was given.
- Exclusively breastfed infants are at higher risk — breast milk is low in vitamin K — and these are often the families most likely to decline.
- India's newborn care guidelines include vitamin K at birth, but home and unsupervised deliveries remain a real gap; ask about place of birth when the history does not fit.
Why it matters
Refusal is climbing in a country where it had almost disappeared, and the harm it produces is catastrophic and entirely preventable.
Don't overread it
This was an observational register study — families who decline vitamin K differ in other ways, and the association is not proof of the mechanism, though the pattern of bleeding fits it closely.
The statistics, in plain English
These odds ratios are adjusted, but families who decline vitamin K differ from those who accept in ways registers cannot fully capture — home birth, other declined interventions, later presentation to care — so some of the excess may not be the vitamin K itself. Two features argue the association is real: the effect is far larger for intracranial bleeding (2.91) than for bleeding generally (1.52), which is the specific pattern vitamin K deficiency produces, and the confidence intervals are tight because the denominator is two million births.
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