 The INTRGIWTH 21st project was designed to develop accurate growth standards for children around the world. This research focused specifically on preterm babies, who often experience different growth patterns than full-term babies. The results of this study found that preterm babies follow similar growth patterns as full-term babies up to 64 weeks postmenstrual age, but that their size at birth does not accurately predict their postnatal growth. Therefore, the INTRGIWTH 21st project developed new growth standards for preterm babies up to 64 weeks postmenstrual age, which can be used instead of size at birth charts. This article was authored by Professor Jose Villa, MD, Francesca Giuliani, MD, Professors Ulfaca A. Butter, PhD and others.