Silas was delivered three months prematurely at the Cedars-Sinai Medical Center in California. And doctors performing the Caesarean section on his mother, Chelsea, were astonished to see his amniotic sac was still intact. Pictures show Silas curled up inside with the placenta and umbilical cord, his tiny hands and a leg clearly visible.
The fluid helps to cushion the baby from bumps and injury, as well as providing it with fluids it can breathe and swallow. It also maintains a constant temperature for the baby.
Typically the amniotic sac breaks on its own during birth, which is commonly referred to as a mother's 'water breaking'.
Or during a C-section, the surgeon cuts through it to deliver the baby.
Doctors say the chance of the amniotic sac remaining completely intact after birth is 'ultra rare'.
It was a moment that mesmerised Dr William Binder, who delivered Silas.
'Even though it sounds cliched, we caught our breath,' he said. 'It really felt like a moment of awe... and one that will stick in my moment for some time.
After taking a few seconds to snap the incredible sight in front of him, Dr Binder set to work removing Silas out of his amniotic sac and getting him breathing.
'It was definitely like a clear film where you could definitely make out his head and his hair,' she told CBS News.
'He was kind of in a foetal position and you could see like his arms and his legs curled up.
'It was actually really cool to see. And when I heard that was actually really rare I was like "oh my gosh you're a special little baby".'
Despite being born at just 26 weeks, Silas is doing so well that doctors hope he will go home within the next month.
Actress Jessica Alba has spoken out about her daughter Haven who was born inside the amniotic sac in 2011.
She said at the time: 'The doctor had never seen anything like it before. He grabbed the nurse and said: 'Look at this!'.
'I was in the middle of pushing and he told me to hold on a minute and not to push.
'He was wearing basketball shorts and a T-shirt and said: 'Oh I have to get my scrubs on for this!' The sac burst on its own after she came out. It was a trip.'
In fact Jessica's experience inspired Haven's name.
She explained: 'When I was in recovery we still hadn't chosen her name. [Her father Cash Warren] picked her up and said she came into the world in her 'safe haven' and [her name] clicked right then for both of us.'
Culled from UK Daily Mail