In an interview with Stellar magazine, the 47-year-old describes how Sara nearly lost her life after developing a severe form of pre-eclampsia during her pregnancy with their daughter, Madison, now two.
‘I remember the doctor looking deeply concerned. Later, he said Sara was really ill and wouldn't have lasted another 24 hours,' Glenn said of the emergency birth.’
Her lungs were filling with fluid and she was struggling to breathe.
'Afterwards he told us Sara was one of the worst two cases he'd seen in his career,' the sports star went on to say.
Sara was forced to go into labour seven weeks earlier after waking one morning with a severe pain in her ear.
With her blood pressure taken, she was rushed to the hospital and diagnosed with life-threatening pre-eclampsia.
The condition saw doctors administering countless steroids to build up the unborn baby's lungs, however this only declined Sara's health, requiring emergency surgery.
Fortunately, Sara survived and gave birth to the couple's first child together.
Glenn tragically lost first wife Jane to breast cancer in 2008, after a decade-long battle.
The couple, who shared two children together, son James, 17, and daughter Holly, 16, created charity The McGrath Foundation in 2005, three years before Jane's death.
Glenn and Sara will be raising funds for breast cancer when they take part in the New York marathon this November.