Background Mothers are encouraged to maximise close contact with their premature infants and to express breast milk. Prolactin is a key hormone of lactation but little is known of levels following premature delivery.

Aim To compare serum Prolactin levels for 6 weeks after birth in lactating full-term mothers with mothers expressing milk for babies of <32 weeks gestation.

Method Weekly samples were obtained from 9 full-term lactating mothers and 9 mothers of premature infants.

Results There was no significant difference in maternal levels post delivery. In all subjects the levels declined progressively over 6 weeks. From weeks 3-6 there was a significant difference between the two groups with lower levels in the preterm group (Term mean 1186mU/1 SD 737: Prem mean 492mU/1 SD 255 p = 0.02).

Conclusion Initial Prolactin levels are not significantly different after premature delivery despite the lack of the normal third trimester rise. A difference appears after three weeks post partum. Influences on this include physical separation of mother and baby and mechanical expression of milk rather than suckling.