Why do jurists consider two years to be the maximum duration of a pregnancy?

The maximum gestation period according to the Maliki, Shafi'i, and Hanbali schools is four years. The Maliki school also has an opinion of five years. The Hanafiyya school, and a narration from the Hanabila, state it is two years. Scholars based this on an inductive study of women's conditions, as it was narrated from Malik, may Allah have mercy on him, that the neighbor of Muhammad ibn Ajlan conceived three pregnancies in twelve years, each pregnancy lasting four years.