Scientists have claimed they have found a way for women to have babies without men by creating artificial sperm.
The team from China claim they have created healthy mouse babies by injecting laboratory-made sperm into eggs to produce mouse offspring.
The scientists claim their stem cell technique could pave the way for new treatments for male fertility.
But British experts have called for the results to be independently verified and pointed out that any practical application is likely to be a long way off.
The mouse cells produced were technically “spermatids” – undeveloped sperm that lack tails and cannot swim.
Yet when they were injected into mouse eggs, mimicking a common IVF technique called Icsi (intracytoplasmic sperm injection), they delivered viable embryos and healthy, fertile babies.
In the UK, using spermatids in the same way to produce a pregnancy would be illegal.
Dr Jiahao Sha, from Nanjing Medical University, who co-led the research, published the results in the peer-reviewed journal Cell Stem Cell.
He said: “If proven to be safe and effective in humans, our platform could potentially generate fully functional sperm for artificial insemination or in-vitro fertilisation techniques.
“Because currently available treatments do not work for many couples, we hope that our approach could substantially improve success rates for male infertility.”
The scientists began with stem cells taken from mouse embryos which were exposed to a carefully mixed cocktail of chemicals.
This triggered their transformation into primordial germ cells, the first step on the developmental path to becoming sperm.
Next, the germ cells were exposed to testicular cells and testosterone in an attempt to mimic the natural environment of the testes.