A court in Germany has denied a request by a transgender man to be registered as the father of a child he conceived in 2013.

The Federal Court of Justice (BGH) ruled that whomever gives birth is considered a child's mother, claiming "the roles of father and mother are not interchangeable."

Oscar Müller legally transitioned in 2011, the same year the Federal Constitutional Court ruled it was possible to change legal gender without surgery. In 2012, Müller became pregnant via artificial insemination, using sperm from a donor who forfeited his parental rights.

His son was born in March 2013.

But the birth registry refused to list Müller as the child's father, entering him as "mother" and using his female birth name. Appeals to district courts in Schöneberg and Berlin failed, so he took his case to federal court.

Although Müller is not considered a woman in the legal sense, German civil code states that "the mother of a child is the woman who gives birth." The BGH maintained that, according to Transsexuals Act of 1980, a person's gender assigned at birth is relevant in regards to any children they have—whether conceived before or after transition.

The provision saves the child from "embarrassing situations," the court ruled, and will allow Müller's son to later register his sperm donor as his biological father if he chooses. The German Society for Trans Identity and Intersexuality (DGTI) condemned the ruling, and hopes it will be overturned by the Constitutional Court.

There are approximately 100,000 transgender people living in Germany, with 1,600 applications to change legal gender filed each year.