A handful of preliminary studies in recent years has raised hopes the epidemic of U.S. child obesity has stabilized or reversed. But new research finds continued growth in American children’s girth, suggesting that self-congratulation would be premature.

Among children from infancy through age 18, rates of obesity have increased steadily from 1999 to 2014, and the numbers of children with the severest forms of obesity have risen most dramatically, a new study finds.

About a third — 33.4 percent of American children in 2014 — were overweight, and just over half of those — 17.4 percent of all children — weighed in as obese.

While most obese children are classified as having Class I obesity, about a third of obese youths are thought to have severe obesity.

Recognizing weight problems or obesity in a child is complex, and parents are notoriously bad judges of whether their children’s weight is worrisome.

Rates of obesity among all American children have risen from 14.6 percent in 1999-2000 to 17.4 percent in 2013-14. The severely obese were a small slice of the population in 1999. But the percentage of children categorized with Class II and Class III obesity has risen steeply over the same period: from 4 percent to 6.3 percent for Class II-or-above obesity and from 0.9 percent to 2.4 percent for Class III obesity.

The new study, published Monday in the journal Obesity, dims optimism prompted by research published two years ago, when a similar population-wide study found a large drop in obesity rates among toddlers, ages 2 to 5. The decline was hailed as the possible leading edge of a reversal in U.S. child obesity.

The authors of the current study, researchers at Duke University, University of North Carolina and Wake Forest University, dashed even that small glimmer of hope. The reported decline, they wrote, “is not evident in our results, for girls or boys.”

Amid widespread efforts to improve children’s diets and boost their physical activity levels, other studies have documented stabilization or reversal of obesity rates in smaller segments of U.S. children, including in California, New York, Philadelphia and in some counties of Mississippi.

Those pockets of progress may still exist. But the current study suggests they are being washed out by continuing, surging growth in child obesity rates.