Growth of Breast-Fed Infants Deviates From Current Reference Data: A Pooled Analysis of US, Canadian, and European Data Sets

Abstract

The sample sizes of infants from the selected studies are shown in Tables 2-4, categorized by duration of breast-feeding, timing of introduction of solid foods, and use of infant formula or other milks. Table 5 shows the cross-tabulation by duration of breast-feeding and age of introduction of supplemental milk or formula. In total, 453 infants were included, of whom 226 were breast-fed for at least 12 months. Of these 226, 141 were not regularly given other milks or formula during the first year of life. Of the total sample, solid foods were introduced at 4 to 5 months to 42% (Table 3), at 6 to 7 months to 38%, at 8 to 9 months at 17%, and after 9 months to 2%. The samples were relatively homogeneous with respect to average maternal weight, height, and age. Mean pregnancy weight gain in the three studies reporting this ranged from 12.7 to 15.0 kg. Maternal educational levels were generally high: in the studies reporting this as a continuous variable, the overall mean was 15.4 ± 2.4 years of education. Mean birth weight ranged from 3414 to 3605 g. Characteristics of infants categorized by breast-feeding duration are shown in Table 6 (the group breast-fed for 4 to 5 month is not shown, because there were only 10 infants in this category). Mothers who breast-fed for 12 or more months were older and had higher parity and educational levels than mothers who breast-fed for less than 12 months, but birth weight did not differ significantly among groups.