The Two and a Half Men star was worried his wife Brooke Mueller and their sons Bob and Max would die during the premature labour last month.
The 43-year-old actor told US TV show 'Entertainment Tonight': "She would have been in serious jeopardy had they stayed in longer. The boys were seven weeks early so things were still developing.
"Max has something called ejection fracture. It's the volume at which the heart pumps and how much blood the heart can pump. There wasn't anything that any other premature child, especially a twin, doesn't normally go through. Things are gradually going toward normal."
Bob and Max have now both been released from hospital but Brooke, 31 - who married Sheen in an intimate ceremony last May - hasn't recovered from the upset she felt when she first saw them.
She said: "It was scary. I went to the intensive care unit to see them and words can't express how amazing and shocking to see two human beings that came out of me. But I was scared.
"Our babies had so many tubes on them, it was frightening. I didn't have the easiest pregnancy. I had pre-eclampsia, gestational diabetes and cholestasis."
Brooke says her sons are now "doing great", but is disappointed they don't look more like her.
She joked: "They are completely Sheens. They don't have any Mueller genes. I'm like, 'Can I at least have an ear?!' Bob looks identical to Charlie. Everybody at the NICU called him Charlie. And Max looks like Charlie's dad Martin."
Charlie has three other children, daughters Sam, five, and Lola, three, with ex-wife Denise Richards and 24-year-old daughter Cassandra from another marriage.