There's a new warning from parents who think soccer is a safe alternative to other contact sports. A new study, published in the journal Pediatrics, confirms that while concussion rates in many sports are down, girls who play soccer are at nearly the same risk for traumatic brain injuries as boys who play football.

The trend is so alarming that some of women soccer's top pros — Megan Rapinoe, Abby Wambach, Michelle Akers and Brandi Chastain — have pledged to donate their brains to science.

"I smashed into the back of her head. So I broke, orbital fracture and broke my nose and my teeth," Akers told CBS News in June.

The new study looks at head trauma in high school sports. Boys' football had the highest rate of concussion, at 10 per every 10,000 practices or games. Girls' soccer was second, at a rate of eight per 10,000. Boys had a much lower rate. In the 20 sports studied, girls had more than twice the rate of concussions compared to boys.

Olivia Hans, 12, got a concussion in October during a soccer game when she collided with another player and hit the ground. "I've had really bad headaches and I've just been sleeping a lot," she said.

For girls, heading the ball or colliding with another player were the main causes of concussions.

"We're still working with proper diagnosing and management of the concussions. But we're also really trying to promote awareness and prevention," said Dr. Jason Krystofiak, a team doctor for the women's professional team.

There are some theories for the disparity in concussions between boys and girls. It may have something to do with differences in hormones between the sexes, or maybe differences in the anatomy of the neck. Another possibility is that girls may be more likely to report symptoms of a concussion than boys. So maybe concussions in boys are actually more frequent than we realize.