Important definitions for clarity in the discussion of premature baby

Premature baby birth is a significant cause of infant and child morbidity and mortality. In the United States, the premature birth rate, which had steadily increased during the 1990s and early 2000s, has decreased annually for four years and is now approximately 11.5%. Human viability, defined as gestational age at which the chance of survival is 50%, is currently approximately 23–24 weeks in developed countries.

Infant girls, on average, have better outcomes than infant boys. A relatively uncomplicated course in the intensive care nursery for an extremely premature baby infant results in a discharge date close to the prenatal EDC.

Several definitions are important for clarity in the discussion of premature baby birth outcomes. First, gestational age is defined as the age of the fetus in terms of pregnancy duration in weeks, measured from the first day of the last menstrual period and, by convention, gestation is recorded as completed weeks and never rounded up. For example, an infant who is born at 32 weeks and four days is defined as being 32 weeks.