Aston Robinson, 18, lashed out at 16-year-old Kayleigh - who was 24 weeks pregnant - after getting into an argument about her speaking to other boys, it was claimed.
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He repeatedly punched the pregnant schoolgirl before pulling her own tartan scarf tightly around her neck for up to 30 seconds at his parents home in Cheltenham.
After the attack, Robinson fled the scene on his BMX bike, visiting a bookies to check the status of a £20 bet he had placed.
Kayleigh was found unconscious by Robinson's sister and take to Gloucestershire Royal Hospital, where medics attempted to save the life of the teenager and her unborn baby girl.
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Tragically, the baby died a day later - and the teenager herself died three days after the incident, Bristol crown court heard.
A pathologist found 20 injuries to the girl’s body, from bruising to her cheek and arms and legs to ligature marks on her neck.
Prosecutor Christopher Quinlan QC told a jury of six men and six women: "He said he used her scarf and he did it because he was jealous and, in his words, wanted her to 'be quiet'."
He also revealed that this was not the first instance of violence, revealing to the jury that Robinson had punched Kayleigh when she first informed him she might be pregnant, telling her: “This will stop you having a baby”.
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On the day before her death Robinson, also from Cheltenham, sent Kayleigh a text messages in which he told her: “Make sure my name is not on your kid’s birth certificate.”
It was also revealed that Robinson had written to Kayleigh's mother, Helen Bage, from prison, expressing sorrow for her loss.
He reportedly wrote: “I didn’t want that to happen … God took her away in peace, away from my accusations and my controlling behaviour.”
The trial, expected to last two weeks, continues.
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