OBJECTIVE:

To examine the associations of upward crossing of major percentiles in weight-for-length in the first 24 months of life with the prevalence of obesity at ages 5 and 10 years.

DESIGN:

Longitudinal study.

SETTING:

Multisite clinical practice.

PARTICIPANTS:

We included 44 622 children aged from 1 month to less than 11 years with 122 214 length/height and weight measurements from January 1, 1980, through December 31, 2008.

MAIN EXPOSURE:

The number of major weight-for-length percentiles crossed during each of four 6-month intervals, that is, 1 to 6 months, 6 to 12 months, 12 to 18 months, and 18 to 24 months.

MAIN OUTCOME MEASURES:

Odds and observed prevalence of obesity (body mass index [calculated as weight in kilograms divided by height in meters squared] ≥95th percentile) at ages 5 and 10 years.

RESULTS:

Crossing upwards 2 or more weight-for-length percentiles was common in the first 6 months of life (43%) and less common during later age intervals. Crossing upwards 2 or more weight-for-length percentiles in the first 24 months was associated with elevated odds of obesity at ages 5 years (odds ratio, 2.08; 95% CI, 1.84-2.34) and 10 years (1.75; 1.53-2.00) compared with crossing less than 2 major percentiles. Obesity prevalence at ages 5 and 10 was highest among children who crossed upwards 2 or more weight-for-length percentiles in the first 6 months of life.

CONCLUSIONS:

Crossing upwards 2 or more major weight-for-length percentiles in the first 24 months of life is associated with later obesity. Upward crossing of 2 weight-for-length percentiles in the first 6 months is associated with the highest prevalence of obesity 5 and 10 years later. Efforts to curb excess weight gain in infancy may be useful in preventing later obesity.