I would say that is because Marie-Ann, the farm girl, has not been pregnant. You can get a couple of scenes where you drink breast milk from Heloise and/or Enid. Both of them can get pregnant and give birth within the time frame of the story. There is also a dream sequence where you drink from an imaginary Adeline's breasts, it is a figment of Heloise's power. That scene doesn't have art, but you get the worded descriptions.