Case-control studies of relation between childhood cancer and neonatal vitamin K administration.

OBJECTIVE: To investigate the possible link between neonatal administration of intramuscular vitamin K and childhood cancer.
DESIGN: Matched case-control study.
SETTING: Selected large maternity units in England and Wales.
SUBJECTS: Children with cancer born 1968-85, diagnosed 1969-86; controls matched for sex, month of birth, and hospital of birth. MAIN EXPOSURE MEASURES: Neonatal administration of vitamin K, length of gestation, birth weight, type of delivery, admission to special care baby unit.
RESULTS: After exclusion of cases with missing notes or unknown hospital vitamin K policy, 597 cases and matched controls were studied. Written records on the use of vitamin K were available for only about 40% of these, and to avoid possible bias from selective recording it was assumed that the stated hospital policy was followed. The association between cancer generally and intramuscular vitamin K was of borderline significance (odds ratio 1.44, P = 0.05); the association was strongest for leukaemia. There was, however, also an effect of abnormal delivery, which could explain some of the findings.
CONCLUSIONS: The lack of consistency between the various studies so far published, including this one, and the low relative risks found in most of them suggest that the risk, if any, attributable to the use of vitamin K cannot be large, but the possibility that there is some risk cannot be excluded. A comparison of the predicted consequences of various policies shows that even a 10% increase would imply that prophylaxis using the commonly recommended 1 mg intramuscular dose should be restricted to babies at particularly high risk of vitamin K deficiency bleeding; alternatively a lower dose might be given to a larger proportion of those at risk.