When I read about corsets, I always wonder what pregnant women did. Were they expected to wear corsets as well? If so, were they still laced tightly or was it a special maternity corset? Wouldn't this be dangerous? I'm thinking mainly of U.S. and North America during the Victorian-era, but I would also be interested in hearing about other time periods.
Yes and no. Pregnancy was a very private thing and the idea of confinement (staying home) was a real thing in the latter months of pregnancy. Maternity corsets were a thing, with lacing on the sides to be loosened as the belly grew. They weren't for support either, but mostly structured to minimize the appearance. Women who had worn corsets since they were young needed them for support. Lower status women did not wear the same type of corsets as those worn by richer women, their corsets were looser and many ditched them during pregnancy.
My answer focuses mostly on English practices at the time, so the practice in the new world may be slightly different.
Sources:
Corsets and Conception: Fashion and Demographic Trends in the Nineteenth Century
There were maternity corsets, and they were less tightly laced. Victorian corsetry (and 18th century stays) was more about achieving a smooth silhouette than cranking down the waist, necessarily - this blog post shows a costumer in the same dress with and without a corset, where her waist measurement is the same in and out of the corset, and you can see that it makes a big difference to the overall silhouette even without waist reduction. Some of that is - as described in the post - the optical illusion a rounder waist creates, but a lot of it is bust support. Before the brassiere, apart from bust reducers worn by very buxom women, there was no form of bust support other than the corset.
So a pregnant woman would still need that support, and she would wear a corset to get it. A maternity corset would need to be adjustable, so they had laceable slits either down the entire side of the corset, as in this example from the Victoria & Albert Museum, or just up from the lower edge to the waist, as in this one. (The example from the V&A also is also made for nursing, as these would generally be worn after the child was born as well.) "Maternity waists" were a softer alternative (example shown in this blog post on a mannequin), unboned and often buttoning down the front instead of lacing. Both maternity corsets and waists were made specifically to curve around the body, rather than to press the fetus inward and hide it.
You can find advertisements for them in the 1910s and 1920s; by this time the brassiere was fairly common, and the maternity corsets were more about supporting the belly from below.
In the 18th century, there were similar stays made with a curved center front seam and lacing slits up the sides to allow for the wearer's changing shape - I can't find a picture online, but a drawing from Diderot's encyclopedia is shown in What Clothes Reveal, by Linda Baumgarten. The book has a section on women's clothing and lives during pregnancy, pp. 146-156. (ETA: Here is some of the relevant text from that section.)