A pregnant woman and her unborn baby remain in a stable condition in hospital after she was allegedly stabbed in the chest by her boyfriend's ex-girlfriend.

The woman, aged in her 20s, was taken to Middlemore Hospital in a serious condition after the incident in south Auckland on Tuesday night.

The incident unfolded about 10.30pm in Weymouth when a 20-year-old woman arrived at an address, where a group of people were drinking.

On her arrival there was an altercation between her and the pregnant woman - her ex-boyfriend's new partner, said Detective Inspector Mark Gutry.


The ex-girlfriend allegedly used a small knife to stab the woman.

"The pregnant woman did receive a stab wound to the side of the chest. It hasn't impacted on the child at all," Mr Gutry said.

The 20-year-old woman has been charged with assault.