NEW YORK — Can a genetic test identify newborns at risk of becoming severely obese by middle age? Researchers say they have come up with one, and that it might allow interventions in childhood.

The test examines more than 2 million spots in a person’s genetic code, seeking variants that individually nudge a person’s obesity risk up by a tiny amount. The researchers drew on previously published data to create a risk score.

A high score didn’t guarantee obesity, nor a low score rule it out. But middle-aged people with scores in the top 10 percent were 25 times as likely to be severely obese as those in the bottom 10 percent, scientists reported in a paper released Thursday by the journal Cell.

Those two groups were separated by an average weight difference of about 29 pounds, researchers said.

Analysis showed the genetic propensity to obesity began having an effect on weight around age 3. Up to about age 8, “you might be able to make a difference in the kids who are born susceptible to obesity,” said one author of the study, Dr. Sekar Kathiresan of Massachusetts General Hospital in Boston and the Broad Institute of MIT and Harvard.

But it will take further research to see whether intervening would work, Kathiresan said.