Sucking pressure and its relationship to milk transfer during breastfeeding in humans

Breast sucking pressure has been only partially characterized in humans and its quantitative relationships with milk transfer and endocrine maternal responses are unknown. A method to record sucking pressure and milk transfer during complete sucking episodes is described. A tubing connected at one end to a pressure transducer was attached to the nipple so that the baby sucked both the nipple and the catheter during breastfeeding. The transducer's signals were fed into a commercial computer system designed to digitize and analyse physiological signals. A total of 27 recordings, 13 of which were from a single breast and 14 from both breasts were evaluated. Average values for the mean and maximum sucking pressures were -50 and -197 mmHg, respectively; the median intersuck interval was 0.7 s; and duration of the sucking episode was 7 min. Diverse sucking pressure patterns were observed due to different mixes of sucking bursts with steady sucking and stable versus decreasing pressure and frequency throughout each sucking episode. The amount of milk transferred to the baby was estimated from the difference in body weight immediately before and after each episode. Milk transfer from the second breast was 58% lower than from the first; this was associated with a significant decrease in grams of milk transferred per suck or per minute without significant changes in sucking pressure. The data suggest that there is a change in the maternal physiological response to sucking between the first and second breast. This report shows the feasibility of measuring the sucking pressure developed by human babies during complete nursing episodes, and offers great potential to explore the relationships between the physical parameters of sucking and maternal physiological responses, such as hormonal changes, milk yield and duration of lactational amenorrhoea.