Lactation and reproduction in Western Australian women.

There has been an increase in the incidence of breast-feeding in industrial areas, particularly in Western Australia, where one in four infants is breast-fed into the second year of life. Most of this increase in the incidence of breast-feeding is found in the higher socio-economic groups, pointing to a need to collect data on milk yield in such women. The levels of milk yield in women with infants between 1 and 6 months ranged from a mean of 1.13-1.24 kg/24 h. This is a higher level of milk production than the generally accepted range of 0.7-0.9 kg/24 h. However, this difference is due, in part, to a failure of previous test weighing methods to correct for the evaporative water losses in either the infant or mother. There was no relationship between the introduction of solids and a return to fertility in 38 women breast-feeding on demand. The return of the ovulatory menstrual cycle in women resulted in two acute changes in milk composition. These changes were characterized by a rise in the concentration of sodium and chloride and a fall in the concentration of potassium, glucose and lactose in breast milk. The first change occurred five to six days before ovulation, and the second occurred six to seven days after it. Following the cessation of breast-feeding, the concentration of lactose in breast milk gradually declined, but the concentrations of anti-bacterial proteins (IgA and lactoferrin) gradually increased to high levels over a period of 30-40 days.(ABSTRACT TRUNCATED AT 250 WORDS)