This
list at goodreads, although including many modern diaries, should help you get off to a good start.
A brief search suggests that maternal mortality before the mid 1800s was around 5 per 1,000 births. That's about 50 times higher than the current rate.
The interventions of doctors in the 1800s and early 1900s actually increased the maternal mortality rate, due to lack of hygiene resulting in more deaths from sepsis.