The victim, 29, was being treated for serious injuries with doctors monitoring her unborn baby.
Police said her injuries were “not believed to be life threatening”.
It is understood the woman, 37 weeks pregnant, turned “to protect the baby” and was knifed twice in the back.
Armed police raced to the scene yesterday after the mum was found in a pool of blood on a pavement in Aberfan, South Wales. Neighbours ran into the street with blankets while emergency services arrived.
The knifeman fled and three schools and a community centre were locked down.
A 28-year-old from Merthyr was later arrested.
Locals said the victim had moved to the village recently from England.
Villager Gareth Jones, 64, said: “This man came out of nowhere and stabbed her.”
Police said the suspect was known to the victim.
The attack was near the scene of the 1966 disaster when 116 children and 28 adults died when a colliery tip fell on Aberfan’s school.
