Nursing assistant Sarah Bradbury from Portland, Dorset, was in the middle of an Advent confession with her priest when she fell ill last Tuesday.
Despite frantic efforts from a doctor in the church, she died later in hospital from a gastro-intestinal bleed.
Her 36-year-old husband Scott said: "All Sarah wanted to do was to become a mother. The one thing keeping me going is Joseph. He can sense something is wrong because his mum isn't around."
The couple had been trying for a baby for 10 years before Sarah became pregnant with Joseph in March 2010. Little Joseph was born at just 23 weeks and given only a 10% chance of survival. Sarah said at the time he was a "complete miracle."
Scott said his wife had gone into the confession room at St Augustine's Church in Weymouth, Dorset when she collapsed.
He told The Mirror: "As she went into confession, she gave me a cheeky smile. She'd told Father Stephen about Joseph and how well he was doing and then during confession she fell to the floor. It was all very sudden."
Sarah's parents Marion and Stephen Woolrich issued a statement saying: "Sarah was a wonderful and caring daughter and our best friend. She was finally loving life so very much as a mummy – we will miss her more than words can express."
Our thoughts are with the family - what a tragedy.