A man who weighed 558 pounds when a Missouri judge prevented him from adopting a child he and his wife had taken into their home underwent gastric bypass surgery Friday in a bid to win the child back.

Gary Stocklaufer, a 34-year-old truck driver, and his wife claim a judge unfairly discriminated against them because of his weight in deciding to give 4-month-old Max to another couple for possible adoption. The infant from Arlington, who is related to the Stocklaufers, had lived with them since he was a week old.

This is considered the first case where a couple seeking to adopt has resorted to surgery in the increasingly prevalent practice of denying parents adoptions because they are obese, several adoption experts said.

Missouri officials would not confirm the reason Max was removed from the Stocklaufers' home, citing the confidentiality of ongoing court proceedings in adoption cases.

Stocklaufer, of Independence, Mo., dieted before the surgery and weighed 480 pounds when he entered the Renaissance Hospital in Dallas for the pro bono operation that could help him shed more than half his bulk.

"They have legally kidnapped this child," Cindy Stocklaufer said Friday as her husband recovered from surgery. "There's no guarantee losing the weight will change anything, but we have to try."

The Jackson County (Mo.) court is required "to consider the welfare and best interests of the child" which is a "complicated determination," court spokeswoman Kelley Carpenter said in an e-mail.

An adoptive parent's health is one of the factors considered by investigators at the Missouri Department of Social Services, said the department's communications director, Ana Margarita Compain-Romero. She could not comment on the specifics of the case.

James Waits, a lawyer for the couple taking care of Max, declined to comment. Max is in adoptive placement with the couple, Cindy Stocklaufer said.

The Stocklaufers have been married 15 years and are licensed by the state of Missouri as foster parents and cared for children. In November 2000, they adopted another relative, 8-year-old Robert. The same judge who denied their petition to adopt Max approved Robert's adoption after multiple house visits and background checks, Cindy Stocklaufer said.

Even then, her husband weighed more than 500 pounds. "They never even mentioned it when we adopted Bobby, and he was the same size," she said.

Lee Allen, vice president of the National Council for Adoption, said he believes the court has forgotten the best interest of the child in this case, considering the Stocklaufers are the boy's relatives chosen as parents by the birth mother with a previous successful adoption.

"What I'm really, really impressed with is the fact that this man is willing to go to whatever lengths to adopt Max and raise him," he said.

More and more American agencies have started considering the weight of adoption applicants as they place children, said Gloria Hochman, spokeswoman for the National Adoption Center, though definitions of dangerous obesity vary by state agency.

The regulations are designed to insure permanency for the child, she said.

In May, the Chinese government began considering the body mass index of American parents when screening couples' eligibility for international adoption.