Final answer:
A baby is considered pre-term if born before 37 weeks of gestation. By the 38th week, the fetus is considered fully developed and ready for birth.
Step-by-step explanation:
A baby is considered pre-term if they are born at less than 37 weeks of gestation. Full-term pregnancy is typically defined as 36-40 weeks, but by the 38th week, the fetus is fully developed and ready to be born. Infants born before reaching full term are usually smaller than full-term infants because they have had less time to grow inside the uterus. Pre-term birth is a significant cause of low birth weight, with babies weighing less than 2.5 kg (5.5 lb.) at increased risk for complications shortly after birth. It is essential to note that the fetal organs mature and the fetus gains significant weight in the last couple of months, particularly after the 38th week when they are primed for birth.