Ex told to cover eyes before attack: court

A pregnant Sydney woman repeatedly stabbed her ex-husband after telling him to cover his eyes because their young son had a "surprise", a court has heard.

The woman, who cannot be named for legal reasons, is accused of trying to murder her former partner when he came to pick up their four-year-old son from her Neutral Bay home in September 2015.

The Crown alleges the woman said the pre-schooler was playing hide and seek and told the man to close his eyes numerous times.

It's alleged she said "he's got a surprise for you" before putting a tea towel over the man's eyes.

"A short time later (the man) ... felt the sensation of a warm liquid flowing from his chin area," prosecutor Glen Porter said in the Downing Centre District Court on Thursday.

"He saw the accused bring the knife down ... at least once, maybe more."

The Crown alleges the attack was unprovoked and the woman screamed "you're never going to take (our son) from me".

Defence barrister John Korn called the man's version of events "ludicrous" and said the pair had argued after he entered the house.

Mr Korn said the woman was blinded when her glasses fell off as they pushed and shoved, and she was also punched in the head during the fight.

In a panic, she allegedly grabbed a 25-centimetre knife from where she had been making a cheese and avocado sandwich and, unable to see, wielded it in front of her, the court heard.

Mr Korn said she did not know she had injured her former partner until he said words to the effect of "what have you done?"

He also said the jury will hear evidence the former husband was a "controlling, manipulative individual" with a history of lying to suit himself.

"His carefully constructed facade went out the window the moment he punched a six-month pregnant woman in the face," Mr Korn said on Thursday.

"He knew he was in trouble."

The man had surgery after suffering wounds to his chin, collar bone and neck.

The woman was also taken to hospital with two golf-ball sized lumps on her head, the court heard.

The trial will continue on Monday.