Responding to a report of a flooded bathroom, cleaners at New York Methodist Hospital in Park Slope found a fetus clogging a toilet in a first-floor restroom Wednesday night, police said.

A doctor at the hospital determined that the fetus was about 20 weeks old, a hospital spokeswoman, Lyn Hill, said. Because the fetus appeared to be intact, she said, it was probably a miscarriage. She could not say why the mother had apparently attempted to flush it down the toilet at about 8 p.m.

The medical examiner’s office has not yet identified the exact age of the fetus, its gender, and how it died, and won’t be able to for another week. The police, meanwhile, are investigating.

New York law permits abortions until the fetus has reached 24 weeks, unless the mother’s life is in danger, the director of the reproductive rights project at the American Civil Liberties Union, Elisabeth Benjamin, said.

Despite an abundance of security cameras at the hospital, the mother has not been identified, police said.

“I’ve been here 18 years and this has never happened in that time,” Ms. Hill said.

Workers at the hospital said the mother chose the bathroom farthest away from the emergency room, in an area near a health clinic that is closed at night.

“If you feel it’s a miscarriage, the emergency room is right there,” one hospital worker, Joanni Cintron, said. “Why do you have to go to the bathroom?”

Ms. Cintron, who works as a cleaner, said the incident had shaken the members of the night housekeeping staff who found the fetus.

Another hospital worker, Juan Romero, was shocked to hear of the incident as he rode the elevator at the start of his day shift early yesterday. He thought, as did others, that the mother had intentionally aborted the fetus.

“It’s sad,” he said. “Some people can’t have babies and here someone kills their baby, and in a hospital no less.”

Whether the aborted fetus is indeed a homicide depends on several answers police and medical investigators were unable to provide yesterday.

If the fetus were found to be older than 24 weeks and alive before being left in the toilet, the mother could be prosecuted, Ms. Benjamin said. Though unusual, young pregnant women sometimes abort their babies in a panic after carrying them past the normal 12-week limit, after which most doctors will not normally perform abortions. Such incidents highlight the need to provide young pregnant women with better information about their options, all of which are confidential, she said.

“Whether you want to carry to term or terminate a pregnancy, there are lots of ways to do both,” Ms. Benjamin said. “We haven’t, as a society, made people aware of the health care options available.”