Population and study sample
The children enrolled on this study are part of a cohort
that began in April 2004, comprising of all live births at
all ten maternity units in the municipal district.The following
exclusion criteria were used in this study: mothers
who were separated from their children by the justice system
(for example, imprisoned); children with diseases that
contraindicate breastfeeding; those who live in locations
that present a risk to the safety of the interviewer (for example,
due to drug trade, prostitution).The sample size
calculation for this study was based on a 6.0% estimated
prevalence of overweight among children under 5 years
old in the Northeast of Brazil [21], a level of precision of
around 1.25% and 95% confidence, which resulted in an
estimated sample of 526 children. This figure was increased
by 30% to cover predicted losses, resulting in a final sample
size calculation of 684 children. However, data from 672
children followed in the cohort from birth to 72 months
were actually analyzed.