Maxxzandra Ford's son Avery is the heaviest ever baby to be born at St Joseph's Women's Hospital in Tampa, Florida.
The mum didn't even know she was pregnant until about 35 weeks in, according to media reports in the US.
She told reporters that after she rapidly gained weight last autumn, doctors confirmed she was pregnant.
Her baby bump grew so big she was convinced she was having twins.
Avery was delivered naturally after an 18 hour labour, but Debbie Moore, a registered nurse at the hospital, said they would 'definitely not' have recommended a natural birth if they had known how much Avery weighed.
Avery's dad, Allen Denton, said: "I got a linebacker now instead of a fullback."
Avery is in neonatal intensive care after his birth on January 29, but he is already eating double the amount of an average-sized newborn and is expected to go home soon.Maxxzandra, who already has a one-year-old son and a five-year-old daughter, said she 'just melted' when she finally held Avery.
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