Four sheep have become pregnant after having their wombs removed and then reconnected, Swedish scientists say.
It is an important step towards successful womb transplants in humans.
Professor Mats Brannstrom and colleagues carried out an autologous transplant in the sheep - where the same womb is removed and reconnected.
There is still work to do before such transplants are safe as New Scientist reported that half the sheep in the study developed fatal complications.
Details of the research were also presented at the International Symposium on Uterine Transplantation, in Goteborg last week.
Earlier this year a team in New York announced their intention to carry out the first womb transplant in the US using a donor organ from a woman who had died.
The procedure would potentially allow women who have had their wombs damaged or removed to develop a pregnancy and give birth.
A womb transplant has been tried once before, in Saudi Arabia in 2000, but then the womb came from a live donor, and was rejected after three months.
One of the difficulties of a successful transplant is the complexity of the blood vessels that need to be reattached.
Pregnancy would put even more strain on these connections, with very dangerous consequences if something was to go wrong.
Animal model
Professor Brannstrom and colleagues at the Sahlgrenska Academy at Gothenburg University in Sweden carried out autologous transplants in 14 sheep, reconnecting the womb to different blood vessels.
Four have become pregnant. Professor Brannstrom said the pregnancies are now at about 120 days, and the pregnancies will last for another 20 days.
The team will deliver the lambs by Caesarean.
They also now plan to carry out a womb swap between two ewes.
The team had previously achieved successful pregnancies after womb transplants in mice.
When transferring a womb from one person to another, one of the biggest problems would be rejection, especially if that occurred during a pregnancy.
Peter Bowen-Simpkins, a spokesperson for the Royal College of Obstetrics and Gynaecology said it was very important that the proof of principle was tested in animals before being attempted in humans.
"They are going the right way about it, instead of racing off to do the work in humans."
He added that transplant technology in humans had progressed tremendously and it had been shown that certain drugs used to prevent rejection in renal transplants did not harm a baby during pregnancy.
"There are not a huge amount of women who will need this - either those born without wombs or those who have had to have a hysterectomy.
"It's quite exciting but I can't see it is something that will become normal procedure within the next 10 years," he said.
From BBC news
