Pediatricians and other breastfeeding advocates often encourage new mothers to breastfeed their babies for at least the first six months of their infants' lives based on the purported health benefits to both mothers and children. Many breastfeeding proponents also argue that breastfeeding has financial advantages over formula-feeding - breastfeeding is free, they say. But, according to a new study, the notion that there's no cost associated with breastfeeding for the recommended amount of time is patently untrue.

"Breastfeeding for six months or longer is only free if a mother's time is worth absolutely nothing," said Mary C. Noonan, an Associate Professor of Sociology at the University of Iowa, and coauthor of the study, "Is Breastfeeding Truly Cost Free? Income Consequences of Breastfeeding for Women," which appears in the April issue of the American Sociological Review.

The study relies on a nationally representative sample of 1,313 first-time mothers in the United States, who were in their 20s or 30s when they gave birth between 1980 and 1993 and who were employed in the year before their first children were born. Noonan and Phyllis L. F. Rippeyoung, an Assistant Professor of Sociology at Canada's Acadia University, found that formula-feeders (i.e., mothers who never breastfed), short-duration breastfeeders (i.e., mothers who breastfed for fewer than six months), and long-duration breastfeeders (i.e., mothers who breastfed for six months or longer) all experienced earnings losses after giving birth. However, on average, long-duration breastfeeders experienced much steeper and more prolonged earnings losses than did mothers who breastfed for shorter durations or not at all.

"When people say breastfeeding is free, I think their perspective is that one doesn't have to buy anything to breastfeed whereas one needs to purchase formula and bottles to formula-feed," Rippeyoung said. "But, this simplistic view doesn't take into consideration the hidden cost: the substantial income women often lose when they breastfeed for a long duration. To me, I see it as being highly related to how women's unpaid work has always been undervalued."

According to the study, long-duration breastfeeders sacrificed considerable income after giving birth compared to short-duration breastfeeders and formula-feeders, largely because long-duration breastfeeders were more likely to switch to part-time work or to leave the workforce entirely.

"We see that the ability to intensively mother via long-duration breastfeeding is class-biased," Noonan said. "Women who breastfeed tend to be white, college educated, and married. Additionally, on average, women who breastfeed are more likely to be married to college-educated men, men who can financially facilitate women taking time out of the labor force."

The authors noted that there are extremely few datasets that consider both breastfeeding and women's work behaviors. "There are some longitudinal datasets that look at breastfeeding and parenting, but we needed longitudinal data that included information on both breastfeeding and women's work behaviors," Rippeyoung said. "Very recent data with that type of information proved difficult to come by. We hope this study will encourage people to collect newer data looking at breastfeeding and work behaviors, so that we can determine whether the trends we see from mothers who gave birth in the 1980s and early 90s still hold true today. However, there is little to make us believe the trends would be very different."

As for the study's policy implications, Rippeyoung and Noonan said their research highlights the need to consider federal legislation that would more broadly protect the rights of all mothers to breastfeed at the workplace and compensate them for the unpaid labor associated with this type of infant feeding, especially if the government is going to continue to push for women to breastfeed. Until 2010, the authors said, no federal legislation existed in this arena, which meant that employers were not bound by federal law to accommodate or not discriminate against breastfeeding mothers. The Patient Protection and Affordable Care Act of 2010 includes limited protections for breastfeeding that simply ensure women get breaks to express their breast milk during the work day and have non-bathroom space where this activity can take place.

"Currently, breastfeeding promotion focuses almost exclusively on encouraging women to breastfeed - without providing adequate economic and social supports to facilitate the practice - a reality that helps reproduce gender, class, and racial inequality," Rippeyoung said. "Legislation more supportive of breastfeeding would include paid parental leave and onsite daycares. Unless these or other policies are put in place, formula-feeding will continue to be the only realistic option for many women in the United States."