Data from birth records with information on previously born children from three maternity hospitals in Norway have been used to study the trend in breast-feeding practice from 1860 to 1984. During the whole period, the percentage of women breast-feeding for at least 1 week was remarkably high, above 90%. The results show a fairly stable duration of breast-feeding up until 1920, at least 3 months in approximately 80% of the women. After that year, the distribution of the duration of breast-feeding changed dramatically. The shortest durations were found in the late 1960s, when only about 30% lactated for 3 months or more. The duration then increased quickly, so that at the beginning of the 1980s about 80% of the women were again breast-feeding for at least 3 months.
By multiple regression methods, the relationships of several independent variables to the duration of breast-feeding were investigated. Married women lactated for 1·5–3 months longer than unmarried, the difference being largest before 1920. First-born children were breast-fed for a little shorter time than second and later-born children. Until World War II women of lowest social strata had the longest durations of breast-feeding, and then the situation was reversed, women of highest social strata continuing the longest.