In Sweden, infants who were born under 2500g receive Niferex, an iron supplement. The idea is that this supplement helps those children grow faster.
Is there any evidence that Niferex helps "catch up" growth?
According to this source, very small children grow very quickly without Niferex. However, oral food is too low in iron to sustain such a growth rate and there is a risk of iron deficiency. That is why Niferex is given to those children.
"Babies that are born prematurely or have a low birth weight (under 2,500 g) will not have been able to obtain sufficient iron while in the mother's womb. Because of the rapid growth rate of very small children, there is a risk of iron deficiency occurring." – From site Niferex.se
Also see Iron Therapy for Preterm Infants for an independent source (thanks to commenter "nobody")
Edit: From this french medical TV show children born prematurely will usually have a normal height within 2-3 years. Sometimes they do not and are medicated with growth hormone.
"Pour la taille, les enfants prématurés rattrapent peu à peu leur retard. Ils croisent les courbes et généralement avant l'âge de deux ou trois ans, les enfants prématurés rattrapent totalement leur retard. De temps en temps, ils ne rattrapent pas leur retard. Dans ce cas, on leur donne de l'hormone de croissance." – Dr Annie Maurel, neuropediatrist – Allô Docteurs, 23/04/2013, France 5.