Postpartum haemorrhage in high-resource settings: variations in clinical management and future research directions based on a comparative study of national guidelines by de Vries, PLM, Deneux-Tharaux, C, Baud, D, Chen, K, Donati, S, Goffinet, F, Knight, M, McLintock, C, D'Souza, R, Sueters, M, van den Akker, T