Joseph Docherty accused his victim of trying to lose weight for a former partner and rowed with her over a ticket for a pub event after drinking celebratory New Year champagne.
Docherty plunged the weapon into Emma Louise Orr’s left leg below the knee with the handle touching her flesh as the tip almost went through the other side of her limb.
The victim said blood came out of her leg “like a rainbow” and she thought she would die after the attack at her home on January 1 this year.
A judge told Docherty (35): “Having carried out this appalling assault you then told her to ‘shut up’ and instructed those present that no one was calling an ambulance.”
Lord Mulholland said: “This was a cowardly and nasty attack on a defenceless, pregnant woman. This is serious domestic violence.”
The judge told Docherty at the High Court in Edinburgh that he would have jailed him for nine years for the crime, but for his early guilty plea.
Docherty earlier admitted assaulting his partner to her severe injury, permanent disfigurement and impairment and to the danger of her life at a house in Redwood Crescent, Viewpark, in Lanarkshire, by biting her on the face and striking her on the leg with the machete.
The victim was left severely scarred and with a limp and now requires lifelong treatment for circulation in the damaged limb.
Defence counsel Derek Ogg QC said Docherty was at a loss to explain his attack on Ms Orr. “It was a momentary loss of control and temper on his part,” he said.
He added: “There is not a long history of any domestic abuse in this case.”
Unemployed Docherty, who has previously been jailed for a disfiguring knife attack, had been in a relationship with his victim, who was about two months pregnant, for just over a year.
Before midnight on Hogmanay the couple were watching TV and drinking champagne to celebrate the New Year.
A friend later joined them but Docherty began asking Ms Orr (28) what she was doing obtaining a ticket for a pub in Bellshill. She asked him what he was talking about.
Advocate depute Blair Speed said: “The accused became argumentative and accused the victim of trying to lose weight for her ex-partner. The victim denied that this was the case and realised that the accused must have seen a Facebook ‘like’ that she had made about a female who had lost weight.”
As a row escalated Docherty bit her on the left cheek and held on to it with his teeth. Docherty later produced a knife and swung it at her left knee and initially missed before inflicting the damaging blow.
The friend lifted up the injured woman and took her to a car before she was driven to hospital. Ms Orr passed out during the journey but woke up to find Docherty screaming at her: “See what you made me do to you so you would tell the truth.”
The friend told Docherty that he had nearly killed her because of the amount of blood she had lost in the attack. Docherty replied: “I didn’t mean it. It was only a carry on with the knife. I didn’t mean to put it in so far.”
The attack victim was operated on and her was opened and surgeons found that main arteries and veins were completely severed along with muscle and nerve damage.
During surgery she was given 10 units of blood and eight plasma packs without which she would have succumbed to her injuries. She later required a skin graft.
Docherty was later detained by police and told them he had knives for hunting but denied stabbing anyone. He told police Ms Orr was pregnant and that was confirmed when she was in hospital