The human gestation usually ends at 40 weeks of gestation, or 9 months.

Prematurity is what we call to all births before 37 weeks of gestation. It represents around 10% of the total life births.

“Ultra”-prematurity represents all births under 6 months of gestation (from week 22 to week 25)

At six months, the organs of the fetus are not prepared to function outside the womb; they are extremely fragile and immature. 

If a baby were to be born at this time, its brain would be easily damaged, its lungs would be unable to breathe, its intestines would not absorb food, and its skin would not retain heat.