The lives of a mother and her unborn son were saved in the first operation of its kind in the UK.
Polly Marshall, 38, was admitted to St George's Hospital in Tooting, south London after suffering severe abdominal pain during her pregnancy.
Doctors discovered a large swelling in the uterine artery supplying blood to her baby, which would have had devastating consequences if it had burst.
Ms Marshall, who was 29 weeks pregnant, underwent an emergency operation to close off the swelling - known as a pseudoaneurysm - in June.
She was able to give birth to son Gus by cesarean section on September 5.
The operation had never been carried out on a pregnant woman in the UK and there is only one other documented case in France, St George's Hospital said.
Dr Kevin Hayes, a consultant obstetrician and gynaecologist who led the team which diagnosed the condition, said it was "extremely rare" for women to develop pseudoaneurysms while pregnant.
He said: "Detailed scans showed that the swelling in Polly's artery was 5cm in diameter and also getting bigger.
"Blood flow through this artery is particularly strong during pregnancy, so we knew doing nothing was not an option."
Medics inserted a fine tube into a "pin-size" hole in Ms Marshall's groin to reach the aneurysm.
Metal coils were then inserted into the artery supplying the swelling to stop the blood flow.
Professor Anna-Maria Belli, a consultant interventional radiologist who carried out the procedure, said: "The fact she was able to undergo the procedure - and carry her baby to term - is a fantastic achievement and has positive implications for other women in her position."
Ms Marshall, from north west London, said it was "amazing" that she could carry Gus to full term.
She said: "I will always be grateful that the problem was identified so early."