Prevalence
Mongolian spots are most prevalent among Mongols, Turks, and other Asian groups, such as the Chinese, Japanese, and especially the Koreans. Nearly all East Asian infants are born with one or more Mongolian spots. It is also common if only one of the parents is East Asian. Among East African infants it is found at rates between 90-95% and 85-90% of Native American infants.
The incidence among Caucasians, that is, the indigenous peoples of Europe, the Middle East, North Africa and the Indian subcontinent (Pakistan, north India, Bangladesh) is between 1-10%.
However, it has been found to be prominent among Europeans that have had extensive interaction with Hun cultures or a central asian origin, most notably the Hungarians who have a 22.6% occurrence rate among their population.
There is an incidence of 50-70% among the countries of the Americas, as a result of the Native American admixture found in mestizos (people of mixed European and Native American ancestry) that is an important racial group among some countries.
Examples:
Ava the Mongolian Baby:
You can't see them very well in the picture, but I assure you they are there. In fact, they were documented at her birth by the doctors and nurses due to the fact that they appear similar to bruises. Should some misinformed soul ever mistake them for abuse, we have all our bases covered.
Where on earth did they come from you ask? After some asking around and digging up family history and heritages, my mom told me I had one as well. She thinks it may have come from her father's side who had Native American Indian influences. Woo hoo!! Add that to the list of traits she's gotten from me so far.