Runners at the Chicago Marathon, Credit: Getty Images

When a 27-year old woman gave birth just hours after completing the Chicago marathon on Sunday, her labor and delivery made national news.

Some of the coverage simply reported the birth of a healthy, 7 pound 9 ounce girl to the mother Amber Miller, who was almost 39 weeks pregnant when she ran her eighth marathon over the weekend. Many of the stories marveled at her athleticism and perseverance.

NEWS: Marathon Running Made Easy, Sort Of

"The race was definitely easier than labor," she said in a news conference the next day.

But the accomplishment also led many people to ask: Is that safe?

Just a decade ago, vigorous exercise during pregnancy was seen as dangerous to the baby. Pregnant women were told to keep their heart rates below 140 beats per minute. With no evidence to support them, those guidelines have been dropped, and doctor's groups are increasingly pushing pregnant women to get moving.

The American College of Obstetricians and Gynecologists advises at least 30 minutes of exercise on most, if not all, days of the week. Among other benefits, physical activity can reduce backaches and constipation, improve mood, energy and sleep, and help women endure and recover better from labor.

VIDEO: How Safe Is It For Marathon Runners To Push Themselves?

After suggesting activities like swimming, cycling and aerobics, ACOG’s official guidelines address running with this advice: "If you were a runner before you became pregnant, you often can keep running during pregnancy, although you may have to modify your routine."

So, how far is too far? It's all relative, suggests a package on pregnancy and running that ran last fall in Runner’s World magazine.

The magazine featured an interview with elite runners Paula Radcliffe and Kara Goucher, who both continued to train throughout their pregnancies.

Goucher said she was still running up to 80 miles a week in her fifth month of pregnancy, was working out twice a day and could still maintain a 4:55 mile pace on some of her runs. Radcliffe had cut back to about 50 percent of her normal training.

Both women were running less distance and with less intensely than they normally do, but they were still doing far more than most amateur runners ever do. And both runners went on, not just to have healthy babies, but also to win or come close to winning marathons within a year after giving birth.

NEWS: Humans Would Beat Neanderthals in a Marathon

While not a professional runner, Miller held way back for her recent marathon. She finished it in six and a half hours instead of her usual three and a half. And she walked about half of it.

Whether women plan to run during pregnancy or not, expecting moms should avoid exercising to exhaustion, recommends the Mayo Clinic. Pregnant exercisers should also make sure to drink enough water, eat enough calories to cover their extra activity, avoid overheating, and stop if they feel any concerning symptoms.

Many experts advise a level of exertion that still allows conversation. And when there's a baby on board, women should always talk to their doctors before starting anything new – like a marathon-training program.