Childhood vaccinations like those for measles– mumps–rubella carry a small risk of seizures. Some parents postpone their children’s vaccinations because they believe the delay decreases the risk. But a new study finds the opposite may be true.

The analysis, published online in Pediatrics, involved 5,496 children born from 2004 to 2008 who had seizures in the first two years of life.

For children who received any of their shots as recommended from ages 12 to 15 months, there was no difference in the incidence of seizure in the 10 days after vaccination compared with the period before vaccination. But compared with giving it at 12 to 15 months, giving the measles-mumps-rubella vaccine at 16 months or later doubled the incidence of seizure, and giving the measles-mumps-rubella-varicella vaccine at that age increased it almost six times.

The risk of seizure after these vaccinations at any age is small — about 1 in 3,000 doses for the M.M.R. and 1 in 1,250 for the M.M.R.V.

“Our study demonstrates a low rate of febrile seizure after the M.M.R. and M.M.R.V. vaccines, and that this rate is increased if the vaccines are received at an older age,” said the lead author, Dr. Simon J. Hambidge, a researcher at the Kaiser Permanente Colorado Institute for Health Research. But, he added, “it is far riskier to delay or avoid vaccination than it is to vaccinate our children.”