CASE-CONTROL STUDIES OF RELATION BETWEEN CHILDHOOD-CANCER AND NEONATAL VITAMIN-K ADMINISTRATION

Objective: To investigate the possible link between neonatal administr ation of intramuscular vitamin K and childhood cancer. Design: Matched case-control study. Setting: Selected large maternity units in Englan d and Wales. Subjects: Children with cancer born 1968-85, diagnosed 19 69-86; 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 car e baby unit. Results: After exclusion of cases with missing notes or u nknown hospital vitamin K policy, 597 cases and matched controls were studied. Written records on the use of vitamin K were available for on ly about 40% of these, and to avoid possible bias from selective recor ding it tvas 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 associatio n was strongest for leukaemia. There was, however, also an effect of a bnormal delivery, which could explain some of the findings. Conclusion s: The lack of consistency between the various studies so far publishe d, including this one, and the low relative risks found in most of the m 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 polic ies 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 th ose at risk.