Prenatal diagnosis of classic hemophilia - Firschein, S I; Hoyer, L W; Lazarchick, J; Forget, B G; Hobbins, J C; Clyne, J C; Clyne, L P; Pitlick, F A; Muir, W A; Merkatz, I R; Mahoney, M J (N Eng J Med, 1979)