First, to describe the prevalence of both full and partial breast-feeding during the first 6 months; second, to study the associations between selected health service-related factors and cessation of full breast-feeding at three time intervals.

Retrospective questionnaires, 6 months after birth.

The Norwegian Mother and Child Cohort Study (MoBa).

In total, 29 621 women.

While 96·6 %, 94·0 %, 90·8 %, 86·9 %, 83·8 % and 80·0 % of the infants were breast-fed at 1, 2, 3, 4, 5 and 6 months, respectively, the corresponding proportions for full breast-feeding were 84·6 %, 79·1 %, 70·9 %, 44·0 %, 16·7 % and 2·1 %. An increased risk of cessation of full breast-feeding during the first month was associated with supplementation during the first week of life with water (relative risk (RR) 1·77; 95 % CI 1·52, 2·06), sugar water (RR 1·73; 95 % CI 1·49, 2·00) or formula (RR 5·99; 95 % CI 5·58, 6·42). An increased risk was also associated with Caesarean delivery (RR 1·08; 95 % CI 1·00, 1·16) and breast-feeding problems (RR 1·56; 95 % CI 1·45, 1·67). Between months 1 and 3, the risk of cessation of full breast-feeding remained elevated in the case of supplementation during the first week of life with water (RR 1·29; 95 % CI 1·14, 1·45), sugar water (RR 1·48; 95 % CI 1·34, 1·64) or formula (RR 1·18; 95 % CI 1·07, 1·29). The same applied to Caesarean delivery (RR 1·15; 95 % CI 1·06, 1·25).

Supplementation during the first week, breast-feeding problems and Caesarean delivery are associated with early cessation of full breast-feeding. The results support a cautious approach to supplementation during the first week of life.