6/6/13 - After a 10-mile training run, Trish Staine was in pain. Not post-training-run pain. Real, excruciating pain. "I was yelling and screaming -- I thought I was dying," says Staine, who was in training for Grandma's Half Marathon in her hometown of Duluth, Minn. at the end of the month. Her family called an ambulance, and when they got to the hospital, they expected a diagnosis of a pinched nerve, a kidney stone, maybe a burst appendix, they told the Duluth News Tribune. But what the nurse treating Staine found was a fetal heartbeat. "And I'm, like, looking around, like, no, I don't believe it," Staine told TODAY on Thursday. She says hadn't missed any periods, she didn't have a "baby belly" -- and her husband, John, had had a vasectomy. But despite all that, Staine soon delivered a healthy girl weighing 6 pounds, 6 ounces. The Staines already have two biological children, ages 7 and 11, and two foster children, plus John's three boys who are 17, 19 and 20. They haven't yet decided on a name, but Trish has an idea. "I wouldn't mind just naming her Miracle, and calling her Mira for short," she told TODAY. This is the kind of story that makes you say, as TODAY anchor Savannah Guthrie did after the interview aired, "REALLY?! Can this really happen?" It can and it does, says Dr. Nancy Snyderman, chief medical editor for NBC News. In the medical literature it's called "denial of pregnancy," and Snyderman cites a British Medical Journal study done in Germany that found 1 out of 475 women who delivered a baby did not realize they were pregnant. There seem to be three general reasons this can happen: One, the woman is very obese, and so does not notice the growing baby belly. Two, the woman is very thin or anorexic, and because of that perhaps already has irregular or skipped periods. Or three -- denial, denial, denial. In obese mothers who didn't know they were pregnant, there can be problems with high blood pressure or blood sugar issues that can put mom or baby at risk. But despite lack of prenatal care, Snyderman believes the Staines' surprise baby will be fine, although she has not treated the infant herself. The story sounds unbelievable, but Snyderman has seen it herself: Early in her medical career, she was treating an obese woman who came into the emergency room complaining of what she thought was a stomach flu. "Guess what, I held a baby," Snyderman says. "I've seen it in person!"