The scientist, He Jiankui, spoke to hundreds of colleagues and journalists on Wednesday at the International Human Genome Editing Summit at the University of Hong Kong.
The second potential pregnancy is in a very early stage and needs more time to be monitored to see if it will last, Dr He said.
He, a former Stanford University postdoctoral fellow who is based at China's Southern University of Science and Technology, said that his team first worked on mice and monkey embryos using a cutting-edge gene-editing technology known as CRISPR to disable a gene that allows the HIV virus to penetrate cells.
On Monday, more than 100 mostly Chinese scientists signed a petition calling for greater oversight by their country on gene-editing experiments, while Southern University said it planned to investigate He's claim, saying the work "seriously violated academic ethics and standards". The US-trained scientist said the twins were born earlier this month. He said the twin girls were conceived to try to help them resist possible future infection with the AIDS virus. "I think it's a puzzling choice and a poor choice", Musunuru says of targeting the CCR5 gene.
But He's speech at the conference was met with anger. "I think there has been a failure of the scientific community because of a lack of transparency".
He Jiankui said he engineered a project that led to the birth of twin girls whose DNA he altered.
Gene editing is a potential fix for heritable diseases but it is extremely controversial because the changes would be passed down to future generations and could eventually affect the entire gene pool.
Liverpool, Chelsea Target Pulisic Could Leave Dortmund
Chelsea are ready to do a £ 70m deal in January for Christian Pulisic - but he will not arrive until next summer. A move in the summer could be on the cards.
He has spoken at the Human Genome Editing Summit at the University of Hong Kong for the first time about his work since the uproar.
"Pandora's box has been opened", they said.
The Crispr gene editing tool he claims to have used is not new to the scientific world, and was first discovered in 2012. Both cause tremendous suffering, are hard to treat effectively, and in rare cases are certain to be passed to any biological children, says Harvard Medical School Dean George Daley, a stem cell scientist.
Daley spoke Wednesday at an global conference in Hong Kong, where the Chinese scientist, He Jiankui (HEH JEE-ahn-qway) of Shenzhen, also is scheduled to speak. He says it is totally inappropriate to use gene editing to select hair or eye color, or to boost IQ; such a use, he says in the video, "is not what a loving parent does".
Facing a packed auditorium of scientists and members of the media, He also acknowledged that he had not made his university in China aware of the research he was doing. Other scientists pointed to now available prophylactic treatments and antiretroviral drugs that can be effective in preventing HIV transmission and infection, saying the procedure was unnecessary.
In 2017, the U.S. National Academies of Science, Engineering and Medicine said lab-only research to learn how to alter embryos is ethical - but said it's not ready for pregnancies yet. "I knew where he was heading", Hurlbut said.
He, who said his work was self-funded, shrugged off concerns that the research was conducted in secrecy, explaining that he had engaged the scientific community over the past three years.
In the United Kingdom and many other countries it is illegal to create genetically modified babies, and scientists in the field have reached a broad consensus that it would be deeply unethical to try.