Dr. Susanna Huh of Children's Hospital in Boston and colleagues said the study involved 1,255 mother-and-child pairs who attended eight outpatient maternity services in eastern Massachusetts from 1999 to 2002.
The mothers joined the study before 22 weeks of pregnancy and their babies were measured and weighed at birth, at 6 months, and 3 years.
Out of the 1,255 deliveries, 22.6 percent were by Cesarean section and the remainder -- 77.4 percent -- were vaginal deliveries.
The study, published online in the Archives of Disease in Childhood, found mothers who delivered by Cesarean section tended to weigh more than those delivering vaginally and the birth weight for gestational age of their babies also tended to be higher. These mothers also breastfed their babies for a shorter period, Huh said.
A Cesarean section delivery was associated with a doubling in the odds of obesity by the time the child was age 3, irrespective of birth weight and after taking maternal weight and several other influential factors into account.
The study found about 16 percent of children delivered via Cesarean section were obese by age 3, compared with 7.5 percent of those born vaginally.