Either during pregnancy or after surgery last September to repair a ruptured tibial tendon - an injury that forced her out of the Glasgow Commonwealth Games - Smith had developed large pulmonary emboli on the lungs.
"Halfway through [my pregnancy] I started feeling bad," Smith said.
"I ran every day until three days before I gave birth, but I was really tired-I would run and then I would have to sit on the couch all day. I just thought it was harder to breathe because I was pregnant. Looking back, I had a lot of the signs that I was developing these clots in my lungs."
Smith told the website that in July she developed a cough and felt breathless, called her doctor who sent her straight to an emergency room.
A CT scan showed many large clots in her lungs. She was transferred to a hospital for surgery.
"They actually put a catheter into your lungs through your neck and exploded the large clots with medicine," Smith said.
"I Googled it before I was getting it and saw that Serena Williams had had that same procedure and was back playing at Wimbledon three months later."
It is the second time Smith has survived a pulmonary embolism, having suffered through one 10 years ago.
She will now be on blood-thinning drugs for the rest of her life, but still hopes to represent New Zealand in Rio next year.
"It's basically rat poison," she said of the drug Warfarin.
"So it's definitely not a good thing [to be on], but it doesn't seem to devastate me too much."
Smith was placed 15th in the marathon at London, but doesn't think she'll have time to meet the New Zealand Olympic Committee's standard of 2h 27m, recover, then run well again over that distance in Rio. Instead she aims to focus again on the track in the 10,000m.
She finished ninth over that distance at the Beijing Olympics. At Athens four years earlier, the Ray Treacy-coached athlete finished 11th in the 5000m.
