Even though the baby, born at 26 weeks, had left mother Chelsea Phillip's womb, because he was inside the amniotic sac he continued receiving oxygen through the placenta, only taking his first 'proper' breath after doctors broke the sac.
The amniotic sac is a bag of clear liquid, in which the unborn child develops until their brith. The sac usually breaks at the beginning of child-birth, and is referred to as the mother's water breaking.
In the photograph, Silas's hand can be seen pressed against the sac with the rest of his body just visible through the delicate membrane still surrounding him.
Californian baby was delivered by C-Section almost 12 weeks ago.
Photo / YouTube
Ms Phillips was unaware her baby had caused an upset in the delivery room until hours afterwards when he mother showed her a photograph taken by one of the doctors present.
The new mother described her son, who is now home and reportedly doing well, as "a little fighter".
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."
Jessica's experience inspired Haven's name.
"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."
The amniotic sac: a mysterious membrane
The amniotic sac starts to form and fill with fluid within days of a woman conceiving.
Amniotic fluid is mainly water, but from about week 10 onwards, the baby passes small amounts of urine into the fluid.
The amount of amniotic fluid increases gradually during pregnancy until about week 38, when it reduces slightly until the baby is born.
Being born "en caul" is the term used when the child is born within an intact amniotic sac, which occurred in the story above. It is also known as a "veiled birth".
Most en caul births occur in premature babies.
Statistics relating to such births are sparse, but deliveries involving any form of caul are thought to occur in roughly one in 80,000 births.
Being born "with the caul", as it is known, occurs when a child is delivered with a portion of amniotic membrane on their face. "Caul" literally means "helmeted head" or "veil".
Being born with the caul in medieval times was interpreted as a sign of good luck and that the child was destined for greatness.
Saving the caul was considered an important tradition of childbirth. The midwife would rub a sheet of paper across the baby's head and face, pressing the material of the caul onto the paper.
It would then be presented to the mother, to be kept as an heirloom.
Other traditions have linked the caul to fertility and some say it protects a person from the forces of evil, such as witches and sorcerers.
