Dear Sue, Here is a citation regarding the difference between pumped and expressed breastmilk. Lang S, Lawrence C, Orme R. Sodium in hand and pump expressed human breast milk. Early human development 1994; 38:131-8. For anyone who is interested, the abstract is as follows: Sodium content was analysed in the expressed breast milk from 30 mothers. Measurements were taken up to 24 days postpartum, during which time the mothers expressed manually or by means of a pump. Statistical analysis has confirmed not only the known decline in sodium levels postpartum but has also shown a significantly higher sodium content in manually expressed milk compared to that from pump expressed milk. This finding suggests that the method of expression may alter the sodium concentration in human breast milk, thus potentially reducing the amount of sodium supplementation required by some preterm infants. Shirley Gross M.D.,C.M., C.C.F.P. Edmonton Breastfeeding Clinic