The 39-year-old singer planned to have baby Ethan at home last year, but had to opt for a Caesarean section in hospital after 20 hours of labour.
In her forthcoming biography, which is being serialised in the Mail on Sunday, she explained, 'Typically for me, nothing about the birth went according to plan. For a start, Ethan arrived ten days early, and then we discovered he wasn't in the correct position for a smooth delivery.
'So, after 20 hours of excruciating labour, my plans for a home birth went out of the window and I ended up having Ethan in hospital... But several hours into my labour my initial serenity had evaporated.
'Because Ethan was in a posterior position, meaning his back was in line with my back and his arms and legs were moving freely across my tummy, I was in absolute agony.
'(The midwives) have since told me how brave I was during those long hours of labour, but not having had a baby before I had no idea at the time whether it was bravery or delirium that saw me through... But when I held Ethan for the first time, the pain and worry melted away... It was wonderful.'