The world’s second three-parent baby has been conceived using a controversial technique

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The world has another three-parent baby, according to The Times. A Ukrainian doctor has treated an “infertile” woman with a controversial in-vitro fertilization technique, resulting in the birth of a healthy baby girl with DNA from three adults. The announcement comes less than a year after an American doctor helped a couple use a slightly different version of the technique to give birth to a three-parent baby boy.

The 34-year-old woman had approached Valery Zukin in his clinic in Kiev after trying to have a baby for more than a decade, including four failed in-vitro fertilization (IVF) attempts. Her embryos were being fertilized successfully, but then stopped growing before one could be implanted in the womb. Such an “embryo arrest” can occur in a small proportion of embryos created via any IVF treatment, but one in 150 women suffer this fate with most of their embryos.

One reason an embryo may stop growing is if it doesn’t have fully functioning mitochondria, the “power plants” inside most biological cells. Mitochondria contain a small amount of DNA—37 of the 20,000 human genes—which children inherit only from their mothers, unlike DNA in the embryo’s nucleus, which comes from both parents. Faulty mitochondria may occur because of faulty DNA or other functional defects. It’s not clear what was the exact problem with Zukin’s patient.

The controversial fix for this is to make a hybrid embryo that combines the parents’ nuclear DNA with healthy mitochondria from another woman—a donor. The technique Zukin used, called pronuclear transfer, involves first creating an embryo using the parents’ egg and sperm. Then, before embryo arrest can happen, the nucleus is extracted and transferred to a donor woman’s egg that has had its own nucleus removed. That egg becomes a healthy embryo, and if all goes well, a healthy child.

Some 30 or so children have been born via a similar method before. However, in 2002, citing ethical and scientific concerns, the US Food and Drug Administration banned its use. After a decade of research and tweaking, however, scientists have carefully started reconsidering the use of new variants of the old technique.

The technique Zukin used was recently legalized in the UK, but only for certain cases, such as for people suffering from genetic conditions called mitochondrial diseases. A patient like Zukin’s wouldn’t qualify. “Pronuclear transfer is highly experimental and has not been properly evaluated or scientifically proven,” Adam Balen, chairman of the British Fertility Society, told the BBC. “We would be extremely cautious about adopting this approach to improve IVF outcomes.”

That doesn’t stop people from trying. Less than six months ago a US doctor used a modified version of the technique in Mexico to help a woman give birth to a healthy three-parent baby boy. The mother suffers from a mitochondrial disease and two of her babies had died at a young age because they inherited the disease from her. The pressure to make it available to such “infertile” women is likely to grow.