Defining gender as a condition determined strictly by a person’s genitals is based on a notion that doctors and scientists abandoned long ago as oversimplified and often medically meaningless.

Researchers who have studied gender issues and provided health care to people who do not fit the typical M/F pigeonholes said that the Trump administration’s latest plan to define gender goes beyond the limits of scientific knowledge.

“The idea that a person’s sex is determined by their anatomy at birth is not true, and we’ve known that it’s not true for decades,” said Dr. Joshua D. Safer, an endocrinologist and executive director of the Center for Transgender Medicine and Surgery at Mount Sinai Health System in New York. He is also president of the United States Professional Association of Transgender Health.

But exactly what does determine gender identity — a person’s powerful, core knowledge of who they are — is not so clear.