Baby Silas Philips was born in 2015, at the Cedars-Sinai Medical Center in California three months premature and still inside his amniotic sac, attached to the umbilical cord.
The video of the delivery was posted to Facebook by Spanish user Jasmine Perez in February 2016 and has been viewed more than 20,000,000 times.
‘Babies born encased within the entire amniotic sac, known as an en-caul birth, is rare and occurs in less than one in 80,000 cases.’
Touched Facebook users commented on the incredible moment.
Noelia Capuani wrote: "I was born this way" while Gerson Mora posted: "This is amazing, I've never seen this."
The amniotic sac is a thin but resilient membrane which encases the baby in fluid to keep it safe during pregnancy. The expectant mum will usually give birth shortly after the casing is split, often referred to as a woman's 'waters breaking'.
Babies being born still encased within the entire amniotic sac, known as an en-caul birth, are rare.
It generally occurs in fewer than one in 80,000 cases.
Dr William Binder, who was present at the birth, said: "Even though it sounds clichéd, we caught our breath.
"It really felt like a moment of awe ... and one that will stick in my moment for some time."