Editing Preterm birth (section)

===Classification===
[[File:Prenatal development table.svg|center|thumb|800px|Stages in [[prenatal development]], with weeks and months numbered from last menstruation]]
In humans, the usual definition of preterm birth is birth before a [[Gestational age (obstetrics)|gestational age]] of 37 complete weeks.<ref name=Steer2005>
{{cite journal | vauthors = Steer P | title = The epidemiology of preterm labour | journal = BJOG | volume = 112 | issue = Suppl 1 | pages = 1–3 | date = March 2005 | pmid = 15715585 | doi = 10.1111/j.1471-0528.2005.00575.x | s2cid = 33738952 | doi-access = free }}</ref> In the normal human fetus, several organ systems mature between 34 and 37 weeks, and the fetus reaches adequate maturity by the end of this period. One of the main organs greatly affected by premature birth is the lungs. The lungs are one of the last organs to mature in the womb; because of this, many premature babies spend the first days and weeks of their lives on [[ventilator]]s. Therefore, a significant overlap exists between preterm birth and prematurity. Generally, preterm babies are premature and term babies are mature. Preterm babies born near 37 weeks often have no problems relating to prematurity if their lungs have developed adequate [[Pulmonary surfactant|surfactant]], which allows the lungs to remain expanded between breaths. Sequelae of prematurity can be reduced to a small extent by using drugs to accelerate maturation of the fetus, and to a greater extent by preventing preterm birth.