Breast-feeding and infant mortality in Norway 1860-1930

Using medical records from maternity clinics in the two Norwegian cities Oslo and Bergen, the effect of lactation on infant mortality during the period 1860-1930 is examined, comparing those who were and were not breast-fed in a total of about 6900 live born infants. The mortality of children not breast-fed was nearly three times that of those who were breast-fed. In a Cox regression analysis the infant's year of birth and the mother's marital status were found to influence mortality in addition to lactation. Children born to unmarried mothers experienced a mortality about twice that of those born to married mothers, both during on-going lactation and in the absence of lactation, up to about 1915. Children born in Oslo had a slightly higher mortality than those born in Bergen. The duration of lactation was found to have a continuing protective effect on infant survival after weaning--the longer the duration, the lower the mortality after cessation of lactation.