Cranial and crebral signs in the diagnosis of spina bifida between 18 and 22 weeks of gestation: a German multicentre study - Bahlmann, F; Reinhard, I; Schramm, T; Geipel, A; Gembruch, U; von Kaisenberg, C S; Schmitz, B; Stupin, J; Chaoui, R; Karl, K; Kalache, K; Faschingbauer, F; Ponnath, M; Rempen, A; Kozlowski, P (Prenat Diagn, 2015)