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By Anita Shah, D.O.:

They want to do it, but many new mothers simply cannot breastfeed.

Some have trouble expressing breast milk, while others struggle to get the baby to latch on or have pain when they do. With the best of intentions, some moms resort to buying breast milk online, which, it turns out, can pose risks.

A study published today in the journal Pediatrics compared 100 samples of breast milk bought online with breast milk from a community "milk bank" where moms donate excess milk. The Internet breast milk contained more bacteria, including strains of staphylococcus and streptococcus. Twenty-one percent of the Internet-sourced samples even included cytomegalovirus, or CMV, a virus that can cause serious neurological effects, compared with 5 percent of the milk bank samples.

None of the samples studied tested positive for HIV.

Study author Sarah Keim, assistant professor of pediatrics at Nationwide Children's Hospital in Columbus, Ohio, said information about the risks and the quality of breast milk bought on the Internet has been limited until now.

"There is no real data," she said. "Just a small study in several countries about why women shared their breast milk."

Other experts agree that purchasing breast milk over the Internet can be very risky.

"Breast milk is a bodily fluid and has the potential to transmit bacterial and fungal infections to a baby who has an immature immune function," said ABC News' senior medical contributor and practicing OB/GYN Dr. Jennifer Ashton. "There is no standardization of the handling or screening. It's like playing Russian roulette with your baby's life."

The U.S. Food and Drug Administration warns against using the Internet as an option for breast milk and recommends "milk from a source that has screened its milk donors and taken other precautions to ensure the safety" of milk, but adds that there are no current regulations restricting the sale of human breast milk.

Doctor's Take

If you can't breastfeed but want your baby to have the benefits of breast milk, the best advice is to be sure your source is safe. If you don't know how the breast milk was collected, stored or shipped, it's probably not worth the risk. Purchasing breast milk over the Internet can harm your newborn, especially if the newborn is premature.

If you're having difficulty breastfeeding, speak to your pediatrician or a lactation consultant. Peer-to-peer support groups can help, too, according to Keim.