"This is the peer reviewed version of the following article: Marlin, N. and Allotey, J. (2019), Baseline 101 – who is who?. BJOG: Int J Obstet Gy. doi:10.1111/1471-0528.15498. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions."