The court decision ended Ms. Serrano’s long struggle to obtain damages for the nurse’s negligence. It also helped her, she said, silence neighbors and others who accused her of lacking maternal instinct and criticized her inability to identify with her own child.

“After four days, how can you not recognize your baby?” Sophie Chas, the lawyer for the clinic, told the newspaper Le Figaro. “We can believe in it when it’s a second, a day, two days. But 10 years? The mothers may have been involved in creating the damage.”

Ms. Serrano answers such disbelief by pointing out that she was 18 at the time and that Manon, now 20, was her first child. “I could never have imagined such a scenario,” she said.

When Ms. Serrano gave birth, the baby developed neonatal jaundice and was almost immediately placed in an incubator. Because of a shortage of cradles, a nurse put the naked baby in the same cradle as another naked baby.

Daniel Verstraete, the lawyer for the other family, which refused to speak publicly about the case, said that only one of the two babies was wearing an identification tag, which “may have fallen off.”

When Manon was handed over to Ms. Serrano after the treatment, mother and child had spent very little time together. Ms. Serrano noticed that the baby’s hair was thicker, but she said she was persuaded to put it out of her mind.