Could you clarify your question? Because in my personal study of history I have never seen any kind of taboo against pregnancy other than out of wedlock

Regarding pregnancy corsets, I would suggest a previous answer of mine here. You may also be interested in the corrections to another poster's answers I gave elsewhere in the thread.

The origin of the pregnancy taboo of the 19th and early 20th century (at least in the Anglosphere - I can't speak to other contexts) appears to be the indelicacy of referring to reproductive organs in general. Books dealing with the subject, for instance, would describe how a woman could detect her own pregnancy through signs like nausea, enlarged breasts, the halting of menstruation, and eventually an increase in girth - some of which would take months to actually develop - even though it was known from the early 19th century that an intimate medical examination by a doctor could discover pregnancy very soon after conception. The idea of a doctor inspecting a woman's vagina was simply too much to be accepted as a regular practice, and there was a certain amount of resistance to the fact that doctors were edging out midwives at this time due to this discomfort.

Childbirth was referred to euphemistically as "the confinement", spurring much modern-day confusion about women being literally confined to their rooms for months as a matter of course, and works of fiction hinted at pregnant characters by noting that they were sewing baby clothes, or by referring to their "condition" (without specifying what sort of condition they were in, except perhaps an "interesting" one). The Victorian Family: Structures and Stresses has a number of excellent examples of novelists talking around the issue.