Females involved in hanky-panky last May and June may have forgotten about it when they crawled into their winter den. Eggs fertilized at that time remained dormant until the start of hibernation when they are finally implanted in the uterus and start to grow. The fetus is still less than an inch long in December and at birth cubs are nine inches long.
In northern climes, birth may occur during the sows sleep. It is interesting to speculate about their reaction, awakening to find newborn cubs beside them, born toothless and blind.
They require lots of mothering in the first few months including protecting them from danger. Wild Mammals of Missouri cites an example of a mother moving her den over two miles, carrying each cub in her mouth. It is no wonder that a mother bear can become a danger to humans when we come too near to the cubs.
Bear encounters are becoming more common in the Ozarks. Ten years ago a bear sighting was big news. Last year, a few miles from Bull Creek, one neighbor identified nine different bears in a season. The population seems to be growing as campers leave food remains in their campfire and people even feed the bears to get pictures.
This really represents the return of bears to their native territory. Henry Rowe Schoolcraft toured southern Missouri in 1818 and his journal is full of references to bear sightings. Schoolcraft's complete journal is available on line and regularly describes bear hunting, eating bear bacon and the high regard hunters held for bears as trade goods. Francis Skalicky's News-Leader article discusses the decline in Missouri bear population to near extinction in the 19th century and its recent recovery.
There is a lot of good information on preventing bear nuisance problems at this MDC web site.