Mothers with more social and financial resources may breast-feed longer than women with less support, a German study suggests.

Pediatricians recommend that infants be exclusively breast-fed until at least 6 months of age because it can reduce their risk of ear and respiratory infections, sudden infant death syndrome, allergies, childhood obesity and diabetes.

Researchers followed two groups of mothers who gave birth in Germany about a decade apart and found that, over time, women became more likely to continue breast-feeding for 4 to 6 months. But these gains were limited to more educated women.

Among less educated mothers, the researchers only saw gains in breast-feeding after accounting for several factors that can get in the way of nursing babies, including a ceasarean delivery or smoking.

"Lower educated women were less likely to overcome these barriers as easily as those with higher education," said study co-author Dr. Dietrich Rothenbacher of Ulm University in Germany.

"If these barriers did not exist, we would have observed a similar improvement in breast-feeding patterns in the lower educated strata" Rothenbacher added by email.

As reported in Pediatrics, Rothenbacher and colleagues analyzed data from one maternity ward for 989 women who gave birth in 2000-2001 and 856 women who had babies in 2012-2013.

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Compared to the earlier group, women in the later group were 21 percent less likely to have stopped predominantly breast-feeding by 4 months and 29 percent less likely to have stopped total breast-feeding by 6 months.

Women with less than 12 years of education had fewer gains in breast-feeding over time, however. By the end of the study period, women with less education were just 8 percent less likely to stop predominantly breast-feeding by 4 months, compared with 24 percent lower odds for women with more education.

One limitation of the study is that researchers lacked data on family attitudes about breast-feeding and any medical conditions that might have influenced how long women nursed, the authors note.

The disparities might look different in the U.S., where a lack of paid family medical leave and differences in access to flexible work schedules might leave poor women with less support for breast-feeding than more affluent mothers, said Jennifer Pitonyak, a researcher at the University of Washington in Seattle who wasn't involved in the study.

"Continuing to breast-feed an infant is challenging when there is a lack of support - particularly for women with lower levels of education and income who may need to return to work as soon as possible after giving birth in order to financially support their family," Pitonyak said by email.

Shifts in public policy or social norms in Germany also might not mirror what's happened in other countries, noted Ruth Newby, a researcher at the University of the Sunshine Coast in Queensland, Australia, who wasn't involved in the study.

What happened in Germany "might be due to shifts in the German economy or in government policy with impacts on things like family income and women's work," Newby said by email.

At the same time, a growing body of research suggests that women's self-confidence and determination may also play a role in neutralizing some of the negative impact of financial or social pressures that deter women from breast-feeding, said Melanie Lutenbacher, a researcher at the Vanderbilt University School of Nursing in Nashville who wasn't involved in the study.

"The take-home message for women if they're thinking about breast-feeding is do your homework," Lutenbacher said by email. "At this point, the burden is still really on the woman for breast-feeding to be successful. She needs to build a breast-feeding support system while still pregnant, identify people from her family and friend circle who are supportive, and learn as much as she can about breast-feeding."