A teenage father accused of murdering his seven-week-old baby pushed his partner to the ground, injuring her face, while she was still pregnant, a court has heard.
The defendant, who was 16 at the time, is accused of killing the boy by biting his nose and "violently swinging or shaking" him at the mother's flat in Southampton, Hampshire, on February 11.
The baby suffered fatal injuries, including a skull fracture, broken leg and rib fractures, in the "deliberate" attack, Winchester Crown Court has heard.
The baby's mother, aged 18 at the time, is on trial for child cruelty for failing to protect her baby or seek help for him.
The trial has heard that residents from a neighbouring block of flats heard "blood-curdling screams" at the time of the alleged attack, which happened in the early hours.
The child's mother, who is now 19, suffered injuries to her face and hands when she was pushed to the ground by the father while pregnant, following an argument in October 2017, the mother's sister told the court.
The sister said: "She said he pushed her with some force and she fell to the floor."
The jury was shown a photograph taken by the sister of the mother's face, which received grazes in the alleged incident.
She added that the mother forgave the father for this.
She added: "She told me he phoned her, he called her a slut, called her a slag and said the child she was carrying wasn't his."
The sister said that she and her partner visited the defendants on the evening before the baby died and said the child was "asleep and calm".
She said: "Everyone was calm, happy. He was asleep the whole time I was there."
The sister added that the mother had been happy to have a baby, and added: "It was like she was born to be a mum."
She said that the death of the child had affected her whole family, and added: "It destroyed us."
A neighbour said that the defendants attended a gathering at another flat in the block where they lived, and said the mother drank vodka and the father, who is now 17, drank Budweiser lager.
She said that during the party she changed the baby's nappy but did not see any injuries on the child.
She added: "He was fine, making funny faces."
The defendants, who cannot be named for legal reasons, deny the charges and the trial continues.