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Jan. 19, 2000 (Los Angeles) -- Mothers who breast-feed the longest are those who plan ahead, according to a study of women in New Zealand in the journal Acta Paediatrica. Researchers found that, of the factors that had the greatest impact on duration of nursing, planning to stop after more than six months was the most significant, followed, surprisingly, by the tendency to develop mastitis, or inflammation of the breast.
"Most of what we found confirmed previous reports in the literature about effects on the duration of breast-feeding," senior author Ed A. Mitchell, MD, tells WebMD. "But we were surprised that mastitis, which is often given as a reason for stopping, here was associated with a longer duration, which is the opposite of what we would have predicted."
To identify factors associated with breast-feeding duration, Mitchell, who is associate professor of pediatrics at the University of Auckland, and his colleagues studied about 330 women delivering healthy, full-term infants at North Shore Hospital in Auckland in 1996. They were able to follow the infants and mothers for one year. During the study period, the mothers were interviewed by telephone about feeding plans, breastfeeding problems, and frequency and duration of nursing.
In the study, 70% of the mothers stopped breastfeeding before their child was 12 months of age. Most breastfed for an average of seven months. The most common reason given for stopping breastfeeding was believed insufficient milk. Other reasons given for stopping included mother's desire to stop and the baby refusing to nurse.
In looking at factors that shorten duration of breastfeeding, researchers found that mothers being under age 25 and returning to full-time work were most strongly associated with shorter duration of nursing.
Inverted nipples, the early introduction of a pacifier, and the use of a bottle in the first month were also associated with a briefer nursing period. "A large number of mothers in our study used formula in the first month of the baby's life, although only a very small number stated that this was their plan at the time of delivery," the authors write.
"Breastfeeding plans described by the mother at the time of delivery were significantly associated with the duration of breastfeeding," the investigators write. Mothers who either had no plans or planned to breast-feed for six months or less, breast-fed for significantly less time than those planning to cease breast-feeding at a specified time after six months.
Mothers who shared their beds or their rooms with their infants for more than three months also had a tendency to breast-feed longer.
The association of mastitis with a longer duration of breast-feeding remains a mystery, but Mitchell offers this hypothesis: "Most mastitis is associated with blocked milk ducts and a stale milk supply, and most women who develop mastitis are abundant producers of milk. It could be that if a woman has a lot of milk, she will breast-feed longer." However, he warns that other studies must confirm this finding before any definite conclusions can be drawn.
"From a practical point of view, the influence of what people plan to do is very important," Mitchell says. Countless studies have proven that breastfeeding significantly promotes development of a baby's brain and improves learning throughout childhood. He adds that prenatal care classes should encourage women to plan to breast-feed for 12 months, and "women should discuss the advantages and disadvantages of breast-feeding for up to 12 months with their partners and health care providers." Babies can thrive on nothing but breast milk for the first four to six months "unless the baby is big and healthy and thirsty -- then the mother may need to supplement the diet." After the first year, he says, "there is minimal evidence to suggest that, in developed countries, continuing to breast-feed adds value."