When the first baby to be conceived using a technique that mixes genetic material from three people was born, in 2016, scientists worried that the procedure had not been studied to show it was safe. Now, scientists in China have conducted the first comprehensive study of the technique in early-stage human embryos, and report that it seems does not seem to affect their development. 

Techniques to create babies with genetic material from three people are designed to prevent mothers with defects in their mitochondria — the organelles that provide cells with energy — from passing them on to their children. Mitochondria contain their own DNA, and children inherit all of their mitochondria from their mother.

“Mitochondrial replacement therapy is a controversial field,” says study co-author Wei Shang, an obstetrician and gynecologist at the Chinese PLA General Hospital in Beijing. “With our research, we hope to provide a foundation for the development of the technique.”