Technically it was planned though it wasn't initially!
The way things go down is Malleus eventually having to find a doctor from the castle that both he and Lilia trust to keep quiet about this since they initially hide the pregnancy from others, especially Maleficia, and then after realizing it's twins they definitely keep quiet on it for safety reasons. But as Lilia gets bigger and since he's so small, it's decided he'll need a C-Section. I headcanon that most non Dragon fae pregnancies go on for around a year so that helps plan things out, though it is still a difficult process because of a fae natural instinct to recoil from their own blood being spilled.