Effectiveness and cost-effectiveness of routine third trimester ultrasound screening for intrauterine growth restriction: study protocol of a nationwide stepped wedge cluster-rando... by Henrichs, J, Verfaille, V, Viester, L, Westerneng, M, Molewijk, B, Franx, A, van der Horst, H, Bosmans, J, de Jonge, A, Jellema, P