I’ve heard the term “wasp waist,” but never really understood it until I came upon an unaltered dress that once belonged to the Empress Elisabeth, known as “Sisi” in Austria. She was a celebrated beauty, married at 16 to her cousin the Emperor Franz Joseph. She pretty much invented anorexia in her age, dieting obsessively and exercising for hours every day. Even after dutifully giving birth to four children, including the required male heir, her waist measured 20 inches for her entire life. Amazingly, her waist was actually had a larger diameter front to back than side to side. I can only guess how it must have felt to be corseted into this dress.
castlesandcoffeehouses.com 
In all probability Sisi had worn a corset from being a toddler – there are examples of baby bodices in mail order catalogues. At this time it was thought that if a small waist was beautiful, then a very small waist was very beautiful. With this logic most 19 century women pulled the stay laces tighter for special occasions. For Sisi, everyday was a special occasion at court. 19 century women did complain about their corsets, but they did want to be beautiful too. And today we complain about high heels, wonderbras, tight jeans etc.
The natural waist of an adult woman today is oval, wider left to right than the front to back measure. It’s difficult to measure your own waist in this way, try measuring someone else! A tight (or very tight) corset tends to make the waist circular. I think that there were ideas that you could make the waist LOOK small from the front if you pushed it into an oval in the other sense – narrower left to right than front to back. I’m not sure how to construct a corset to do this!
Betty
Thank you for this insight! I’m glad baby corsets have gone out of fashion–and wasp waist adult corsets too!