1. Efficacy of threephase oral contraceptives;Schneider, W.H.F.; Spona, J.; Schmid, R.; Lachnit-Fixon, U.,1977
2. A randomized study of metabolic effects of four oral contraceptive preparations containing levonorgestrel plus ethinyloestradiol in different regimens;Briggs, M.; Briggs, M.,1980