[Truncated abstract] Mothers who deliver prematurely often have a delay in lactogenesis II and subsequent milk supply. Furthermore, due to the inability of their babies to breastfeed immediately after birth, these mothers are 'pump dependent' during both initiation and establishment of lactation. Apparently, there are no evidence based guidelines for the expression regime but some data suggesting that expression regimes for both breasts should be at least five times per day and at least 100 minutes expressing time per day. The project was set out to document the self selected current expression regimes of the preterm mothers from day 10 to 60 postpartum. It defined how various aspects of breast expression, such as frequency and interval, impact on the synthesis and production of milk. In addition, it determined the variations in the composition of preterm mother's milk. The collection of 24hr expression data and milk samples at each expression of each breast, each day, of 25 preterm mothers (<32 gestation age) from the neonatal intensive care unit in King Edward Memorial Hospital, Western Australia on day 10, 15-20, 30, 40, 50 and 60 postpartum showed that during the 'pump dependent' period (day 10 20), the frequency of expression for both breasts was 6, 6-7, 3-9 times per day (median, IQR, range) and total duration with the pump was 115, 80-160, 32-320 minute per day (median, IQR, range). Furthermore, during the 'transition from exclusively expressing to exclusively breastfeeding' period (day 30-60), frequency of expression/breastfeed and total duration of milk removal (both expressing and breastfeeding) for both breasts were 6, 5-7, 1-9 and 135, 75-170, 25-320, respectively (median, IQR, range). ... These nutrients make up the energy content of milk, thus the energy content of milk also varied greatly between mothers. Therefore, milk from individual preterm mothers varies greatly for individual values for fat, total protein, lactose and energy and this should be taken into account when calculating the level of fortification required for individual babies. The results suggest that when fortifying mother's milk, weekly measurement of fat and protein in milk would provide good estimates on which to base fortification requirements. The concentration of sIgA plus lactoferrin formed 32% of the total proteins in breastmilk. However there was large variations in the concentration of sIgA and lactoferrin (median, IQR, range: 0.82, 0.59-1.13, 0.05-2.93g/l and 2.41, 1.52-3.52, 0.04-8.82g/l, respectively) between mothers. Therefore the level of protection provided by these two proteins could differ greatly between babies. Further research on the relationship between the concentration of sIgA and lactoferrin in milk and the onset of infection would indicate the minimum amount of these proteins needed for the babies to benefit from the immune protection provided by their mother's milk. The hourly breast expression method and regression analysis of actual milk yield and interval since previous expression provides information that identifies the potential milk synthesis capacity of the breasts of the mothers and the impact of the interval between expressions on the milk production of the mothers. This information can be applied to individualize the interval between expression regimes to optimise milk production and minimize the demand on the mother. In addition, determining the changes in the milk composition of individual mothers would provide a more precise base to fortify their milk for their preterm babies.