The researcher, He Jiankui of Shenzhen, revealed the pregnancy Wednesday while making his first public comments about his controversial work at an worldwide conference in Hong Kong.
He Jiankui told a packed Hong Kong biomedical conference he was "proud" to have successfully altered the DNA of twin girls born to an HIV-positive father, an apparent medical breakthrough. The work has yet to be published in any medical journal, or publicly verified by evidence.
He was elusive at first when asked if there were other genetically modified pregnancies in progress, saying the trial was "paused due to [the] current situation". But she notes, "one of the dangers of this kind of-I feel premature-study is that it muddies the waters and tarnishes the technology in this area at a time when we should be celebrating it and working together carefully to ensure that it's used safely". "There is another one, another potential pregnancy", he said on stage.
On Tuesday, 140 Chinese AIDS researchers released a joint statement saying the experiment had "ignored a scientific and ethical boundary". He claims to have used CRISPR to manipulate CCR5, a receptor gene linked to the contraction of AIDS, in the two human embryos.
"The volunteers were informed of the risk posed by the existence of one potential off-target and they chose to implant", He said Wednesday, as he was bombarded with questions about the trial.
In a statement on Monday, American biochemist Jennifer Doudna, another co-inventor of the CRISPR/Cas9 technology, called on the scientists responsible for the work to explain "their break from the global consensus that application of CRISPR/Cas9 for human germ line editing should not proceed at the present time".
"This is an example of an approach that was not sufficiently careful and cautious and proportionate", he said.
"Clearly however it is a point in history".
Summit chair David Baltimore, a Nobel laureate, said there had been "a failure of self-regulation by the scientific community because of a lack of transparency". "Should such epic scientific misadventures proceed, a technology with enormous promise for prevention and treatment of disease will be overshadowed by justifiable public outrage, fear and disgust", he said.More news: Porsche 911 S and 4S: The All-New 992-Generation Is Here
CRISPR-Cas9 is a technology that allows scientists to essentially cut and paste DNA, raising hope of genetic fixes for disease, but there are concerns about safety and ethics.
But the co-inventor of CRISPR condemned He's trial as risky and unnecessary.
But critics warned that altering genes could leave the girls susceptible to influenza and West Nile fever, with the danger of gene mutation resulting in more severe complications as well as the artificial changes passing onto future generations of the twins hard to be ruled out.
Gene editing is banned in Britain, the United States many other parts of the world, largely because its long-term effects on mental and physical health are poorly understood.
Sohnee Ahmed, president of the Canadian Association of Genetic Counsellors, said that if the Chinese scientist's claim is true, the birth of the word's first genetically altered babies has run way ahead of both scientific maturity and ethical considerations.
China's National Health Commission ordered an "immediate investigation" into the case on Monday, the official Xinhua news agency reported, while the Shenzhen hospital meant to have approved the research programme denied its involvement. Aside from the lack of verifiable evidence for this non-peer-reviewed claim, this research is premature, unsafe and irresponsible.
There is also a history of fraud within China's academic community - including a scandal a year ago that led to the withdrawal of 100 "compromised" academic papers.
"I think we still need to understand the motivation for the study and what the process was for informed consent", said Jennifer Doudna, a co-inventor of the CRISPR gene-editing tool, who watched He speak.
"But University of Massachusetts Lowell assistant professor Nicholas Evans tweeted: "(D) on't get me wrong, privacy is vital here.