Even babies under 6 months old are more likely to be overweight today compared with those 20 years ago, a study of Massachusetts children found.

Fewer than 1 in 10 babies was found to be too fat, but the rate was still up substantially from two decades ago. That's worrisome because research has shown that accelerated weight gain in a child's early months can predict weight problems and higher blood pressure later in life, said senior author Dr. Matthew Gillman, associate professor at Harvard Medical School.

"The results of this study point out very clearly that the origins of overweight are at the origins of human life, even at birth," he said. The study was published this week in the journal Obesity.

The researchers looked at medical records of more than 120,000 children who visited doctors from 1980-2001. All were enrolled in a health maintenance organization that used an electronic medical record system and most came from middle-class families.

Among children 6 months and younger, a group seldom included in weight studies, the percentage of overweight babies jumped from a little over 3 percent in 1980 to nearly 6 percent.

Whether a baby was overweight was determined mostly by change in weight over those first crucial months, especially weight gain out of proportion with length rather than the infant's weight at a specific age, Gillman said.

For the group overall, the prevalence of overweight children increased from 6 percent to 10 percent.

Researchers didn't study why there is a higher rate of fat babies today, but Gillman pointed to previous studies that have connected higher birth weights to mothers who were overweight before or during pregnancy and to those who had diabetes during pregnancy.

"Good habits need to begin at the very beginning of life," said Dr. Louis Aronne, director of the Obesity Center at New York-Presbyterian Hospital/Weill Cornell Medical Center, who was not involved with the study.

Laura Riley, a doctor of obstetrics and gynecology at Massachusetts General Hospital in Boston who was not connected with the research, said she hoped it would give doctors more ammunition in the push to get mothers to make healthier choices before, during and immediately after pregnancy.

"Pregnant women need to be much more aware of what the implications are of what they do," she said. "Yeah, it's cute to be a nice, healthy, chubby baby, but the question is whether there's a point when it's really over the top."

Sara Keng, a 29-year-old stay-at-home mother of three from Woonsocket, R.I., said she wasn't surprised by the study's results. She blames the increase on "super-sized" foods and harried parents who rely on fast foods to feed their families.

Keng said she got a wake-up call when her oldest son, now 4, became overweight when he was a toddler, forcing her and her husband to change family eating habits. She thinks the new study shouldn't drive parents to obsess over their newborn's weight.

But she believes the new data could be more evidence for parents and especially pregnant women that their actions can cause future problems. Holding her 8-month-old son, Brycen, while her other children played in Boston Common, Keng said she sees it firsthand at the playground sometimes.

"Some kids are really big, and that's really scary," she said.