Reproduction

"Cycle" - a hidden variable counting cycle day. Resets to 1 on birth (or termination of pregnancy), and counts as high as 59 (although numbers above 30 are largely meaningless) (source: starting a female character - well, ish. Unfortunately, I had to implement it as a hidden variable for all characters so that male characters don't end up potentially able to see a cycle tracker once they pass time in-game)

"Pregnant" - a simple true/false state
"Pregnancy day" - a hidden day counter which counts down. When it hits zero, birth will happen. Upon reaching a low number, a warning should give the player time to get somewhere safe to birth

Regardless of whether or not players enjoy pregnancy content, with a multi-year in-game time campaign, it is a necessity to consider. Female player characters should thus have warning text leading up to heterosexual sexual encounters reminding them that pregnancy is a risk in event of vaginal intercourse.