A unified protocol is essential to ensure that fetal ultrasound measurements taken in multicentre research studies are accurate and reproducible. This paper describes the methodology used to take two-dimensional, ultrasound measurements in the longitudinal, fetal growth component of the INTERGROWTH-21st Project. These standardised methods should minimise the systematic errors associated with pooling data from different study sites. They represent a model for carrying out similar research studies in the future.

BJOG: Papageorghiou, A, Sarris, I, Ioannou, C, Todros, T, Carvalho, M, Pilu, G, Salomon, L, for the International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st). Ultrasound methodology used to construct the fetal growth standards in the INTERGROWTH-21st Project. BJOG 2013;120 (Suppl. 2): 27–32.