CHICAGO — Keri Christensen spots an empty soda can on the side of the road in McHenry County, and in a flash she is back at the helm of a heavy-equipment transporter maneuvering along Iraq's treacherous highways.

Her two children are strapped into seats in her minivan, but Christensen finds herself scrutinizing roadside trash for signs of a makeshift bomb.

"Everything is weird," said Christensen, 33, a Wisconsin National Guard soldier who returned in November to the Chicago area after serving 10 months in Iraq. "I went from a stay-at-home mom to a soldier instantly."

Traveling that path in reverse has been equally tough for Christensen and an increasing number of other female veterans. Since 2003, the number of former soldiers seeking help for combat-related posttraumatic stress disorder has grown so much that the North Chicago Veterans Affairs Medical Center has shifted its women's mental health program to respond to combat stress disorders.

Formed in 2001, the program was originally geared to help women suffering trauma from sexual harassment to rape. The program still helps women with what the armed forces calls "military sexual trauma." But therapists now are seeing female vets who exhibit the same signs of posttraumatic stress disorder as men who served in infantry units.

"Flashbacks, hypervigilance, sleep disorders. They're always on edge," said Katherine Dong, manager of the Women Veterans Health Care Program at the North Chicago facility, who helped form the mental health program. "If somebody drops a book, they hit the floor."

No one knows the number of vets suffering from wartime stress. But a report released this month by the Government Accountability Office found that at least one in 20 returning vets surveyed were at risk for developing posttraumatic stress disorder; an earlier report by the Journal of the American Medical Association put the number at nearly one in five.

Some data suggest women either experience posttrauma disorders more often than men or are more willing to admit it.

Since women constitute roughly 15 percent of the armed forces and the lines of combat in Iraq are blurred, more of them are being exposed to the life-and-death situations that often trigger stress disorders, experts say.

"There are all these roadside bombs," said Barb Wisott, a former social worker at the North Chicago hospital who recently moved to the VA's Eastern Colorado Health Care System in Denver. "Women driving in convoys and delivering supplies are experiencing more combat exposure."

Though the symptoms are similar in both men and women — nightmares, flashbacks, a fear of crowds, irritability — more women than men are coming home to fulfill the role of primary nurturer. A growing number are finding the transition from soldier to mom difficult, vets and veterans administrators say.

"Women are often trying to reintegrate into a family with young children," Dong said. "They're expected to go back to being with the kids."

For Christensen, that part of her homecoming was especially hard. Sobbing at silly things like patriotic songs on a country radio station was frustrating enough. It was worse to do it in front of her children, Madison, 7, and Olivia, 4.

"I'd try to hold it together in front of the kids," she said.

Between 2002 and 2006, about 20,000 men and 6,000 women were diagnosed with mental health issues, including 2,500 women assessed specifically with posttrauma stress, according to VA data.

But officials caution that the numbers likely represent a fraction of those who suffer from the stress disorder since only about 10 percent of veterans seek medical help at VA hospitals. Some go to private clinics; others may not seek help at all.