A sizable share of the U.S. organizations recruiting egg donors online don't adhere to ethical guidelines, including failing to warn of the risks of the procedure and offering extra payment for traits like good looks, according to a U.S. study.

Women are recruited to donate eggs to fulfill a growing demand by couples seeking in-vitro fertilization (IVF), but a number of websites seeking to recruit them ignore standards set by the American Society for Reproductive Medicine (ASRM).

"I would argue that there needs to be more attention from ASRM about these agencies, because you don't want these women exploited," said Robert Klitzman, a professor of clinical psychiatry at Columbia University and lead author of the study that appeared in the journal Fertility & Sterility.

Ethical standards set forth by the ASRM specify that donors should be at least 21 years old, and those between ages 18 and 20 should receive a psychiatric evaluation first.

Also, women are not to be paid for their eggs but compensated, equally, for their time. Donor traits such as college grades or previous successful donations should not result in higher payment.

But abiding by the recommendations is voluntary, and the guidelines carry no legal authority, though ASRM will sanction members who do not adhere to the guidelines. But that doesn't cover non-member organizations.

"Our ability to influence the behavior of non-members is pretty limited," said Sean Tipton, a spokesperson for ASRM.

To see how well recruiters follow the guidelines, Klitzman and his colleagues visited 102 websites recruiting egg donors. Some represented IVF clinics run by a physician, and others were agencies that connect women with clinics but don't actually provide any of the medical services.

Some 34 percent of the websites offered higher payment for certain traits, most commonly having previously donated successfully. Some also offered higher payments for educational achievement, athletic skills and good looks.

More than 40 percent of the sites also recruited women between the ages of 18 and 20.

Klitzman told Reuters Health the findings are a concern.

"We're not paying for the eggs... but we're compensating people for their time and effort. So, therefore, we shouldn't pay for the quality of eggs," said Klitzman, who directs Columbia's Masters in Bioethics program.

About 26 percent of ASRM approved agencies or clinics paid more for certain traits, versus 63 percent of non-approved sites. Clinics, which have a physician on staff, were more likely to adhere to the recommendations than egg-donor agencies.

"There's no question that there are some agencies that don't seem particularly interested in what our guidelines are, and we don't know how to impact their behavior," said Tipton.

He said the best way to avoid ethical problems is for both potential donors and patients seeking donor eggs to be aware of the ASRM recommendations, and ask if the clinic or agency follows them.

Klitzman said potential donors also need to be aware of the potential risks of donating eggs.

"To donate eggs is not an entirely benign procedure. It's not high, high risk, but you're taking very high doses of hormones, having needles stuck in your ovaries.

"The idea is to help people. The problem is, you want to make sure it's done appropriately and that people are not being exploited or taken advantage of."

The study was published in journal Fertility and Sterility.