Studies in human lactation: milk volumes in lactating women during the onset of lactation and full lactation.

After validation of test-weighing procedures milk volumes produced by 13 multiparous US Caucasian women were followed longitudinally through the 1st year of lactation. All practiced exclusive breastfeeding for at least 5 months. Milk transfer to the infant was low on days 1 and 2 and increased rapidly to 498 +or- 129 g/d (approximately equal to x +or- standard deviation) on day 5 and then more slowly to 753 +or- 89 g/d during months 3-5. There was a characteristic milk volume for each mother-infant pair that was significantly related neither to milk yield on days 4-6 nor to birthweight. It was however strongly related to infant weight at 1 month suggesting that infant and/or maternal factors coming into play during the 1st month of life are strong determinants of subsequent milk transfer to the infant. The subjects in the study were all nonsmokers who planned to continue breastfeeding for at least 1 year. None used hormonal contraception during the study. Mean age at the birth of the study infant was 31.9 +or- 4.4 standard deviation (range 25-39 years). Median family income was US$35000/year. All mothers were high school graduates and all but 2 had college degrees. The data in this study differ in no significant respect from milk-volume data obtained in larger cross-sectional studies from a variety of populations throughout the world. Future studies focusing on the infant factors that influence the demand for breast milk in the 1st month postpartum may be of considerable importance in understanding the growth of the breastfed infant. (authors modified)