Premature birth occurs when a baby is born before the 37th week of pregnancy. The greater the health risks to the baby, the sooner the birth. To help them grow and thrive outside of the mother's womb, preterm newborns require close monitoring and particular care. A preterm, premature, or "preemie" baby is one who is born three weeks before his or her due date. A normal pregnancy lasts about 40 weeks (foetal development). Preterm birth occurs when a woman is 37 weeks or less pregnant. The mother and infant may face major health risks as a result of the premature or early birth. Premature babies frequently require specialised medical attention in a neonatal intensive care unit (NICU). This is a section of the hospital reserved for very ill newborns. Neonatologists are doctors who specialise in the care of newborns. Some babies spend weeks or months in the NICU.