The sooner a new mother goes back to work after giving birth, the less likely she is to breastfeed her baby, according to a U.S. study.

Mothers in the study, published in Pediatrics, who went back to work within six weeks were less likely than other women to start breastfeeding -- and when they did start, they were less likely to continue.

By contrast, mothers who stayed home for at least nine months, or even 13 weeks, were more likely to predominantly breastfeed their babies for three months or more.

Research has shown that breastfed babies have lower rates of a number of pediatric illnesses, including eczema, middle-ear infections, pneumonia and asthma.

"We would encourage all women to attempt to breastfeed and continue as long as they can," said study author Chinelo Ogbuanu at the Georgia Department of Health.

For example, she said, the more women breastfeed, the more milk they produce -- and when they are separated from their babies during the day, their milk supply may start to dwindle.

"No matter how effective a breast pump is, it's not as effective as an infant," Ogbuanu told Reuters Health.

She suggests that women try to take all their maternity leave at once, rather than breaking it up, and find ways to keep their baby close to the workplace during the day so they can breastfeed during work breaks. Failing that, regular pumping will ensure that their supply continues.

Currently, just seven of every 10 women in the United States breastfeed their babies at all, and just three of every 10 continue for a full six months, according to the Centers for Disease Control and Prevention.

Ogbuanu and her team reviewed information collected from 6,150 women who worked before giving birth. In interviews conducted nine months and two years after their babies were born, the women reported how long they had breastfed and when they returned to work.

The women who did not go back to work for at least nine months were more likely to have started breastfeeding that women who said they'd gone back in six weeks or less. About seven of every 10 mothers who were still home nine months later had tried to breastfeed, compared to six of 10 who went back to work within one to six weeks after delivery.

More than three out of 10 women who stayed home for at least 13 weeks said they predominantly breastfed their babies, compared to fewer than two of every 10 who went back to work within six weeks.

The authors did not find any relationship between breastfeeding and total allowed maternity leave, paid or unpaid, but instead focused on how long women took off before returning to work, concluding that the rate of breastfeeding in the United States might rise if new mothers delay their return.

But others said that the lack of a relationship between breastfeeding and total maternity leave made the data somewhat confusing, calling for a large-scale study based on the length of maternity leave.

"Based on their findings, I would not necessarily say going back to work causes some women to stop breastfeeding," said Hawley Montgomery-Downs of West Virginia University, who did not take part in the study.