Preterm and premature birth refer to the same basic principle – when a baby is born before the 37th or 38th week of pregnancy, depending on who you ask. The difference is that premature and preterm are typically used to reference different aspects of a baby born early. Pregnancy in humans has a gestational period of 40 week, with 37 weeks being the common marker for when a baby has fully developed all of their internal organs necessary for their body to function properly. Babies born before that are considered to be premature babies, born through the process of a preterm birth, which is where the difference lies between preterm and premature. Premature babies can be classified in different levels of prematurity, dependent on how early they were born. These classifications are extremely premature for babies born between 25 and 28 weeks or any point before 25 weeks, very premature for babies born before 32 weeks and moderate to late premature in the case of babies born between 32 and 37 weeks. At each level there are different risks and complications associated with babies being born that early, including the likelihood of survival.