If a newborn is born before the 36th week of pregnancy or weighs less than five and one-half pounds, what is this condition called?

The condition described, where a newborn is born prior to the 36th week of pregnancy, is classified as premature. Prematurity is defined by the gestational age of the infant, and any baby born before 37 weeks is considered premature. This classification is crucial as premature infants are at a higher risk for various health complications due to their underdeveloped organs and systems.

While low birth weight often coincides with prematurity, the defining factor in this case is the gestational age rather than the weight. Infants weighing less than five and one-half pounds could be classified as low birth weight, but that term does not specifically encompass the timing of the birth. Additionally, "underweight" and "post-term" are not applicable in this context. Underweight is a general term not specific to gestational age, and post-term refers to infants born after 42 weeks of pregnancy. Therefore, when considering the gestational age, the most accurate term for a baby born before the 36th week is indeed that the baby is premature.