HONG KONG—A Chinese scientist who claims to have engineered the world’s first gene-edited babies confronted his global peers at a conference as critics openly challenged him about the risks and ethics of his experiment.

He Jiankui—who stunned the medical world on Monday when news surfaced he had produced twin girls whose DNA had been edited to resist HIV—also told the Wednesday event a second woman had been implanted with a gene-edited embryo. He didn’t elaborate.

News...