According to He, four experts reviewed the consent form that He later gave to the participating couples. He recalled that for each couple, he, in the presence of other expert observers, spent about 70 minutes explaining to them what the consent form meant, to convince them to sign the form.

The meeting He spoke at was part of the Second International Summit on Human Genome Editing, which began Tuesday and ends Thursday in Hong Kong. Since Monday, when he announced the news of the twin girls, he has been widely condemned by scientific communities in China and abroad for his disregard of ethics.

Professor David Baltimore, chair of the summit’s organizing committee, said before He began taking questions, that it would be irresponsible to proceed with any clinical use of genome editing unless and until the safety issues have been dealt with and there is universal societal consensus.