Chrissy Bernal was six months into her pregnancy when she realised she was having twins - baby Sienna was so small that she had not been picked up on previous scans.
But it was not until six years after her birth that Sienna was diagnosed with primordial dwarfism, a disorder which means she has had a smaller body size than others her age since before she was born.
The sisters were born three months prematurely, with Sienna weighing slightly more than a pound.
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