The events of episode 17 eventually lead to the revelation that
Kokoro is pregnant with Mitsuru's child
In episode 22 New Nana states that this diagnosis was obtained primarily from old-world information regarding hormone levels. New Nana then goes on to state that pregnancy inhibits a Pistil's ability to pilot a Franxx, with the two courses of actions being:
- Stay out of the action until the child is born, or
- Abort the foetus
Which begs the question, was this the first recorded instance of a Pistil becoming pregnant? From Original Nana's flashback in episode 18 we know that
Neither Kokoro and Mitsuru, nor Hiro and Zero Two are the first Parasite pairing to fall in love
But how is it known that pregnancy interferes with the ability to pilot a Franxx if she is the first of her kind to be affected?