Significantly more women in the fennel ( 73 % ) and LD-COC ( 81 % ) groups experienced menstrual bleeding compared to the placebo ( 19 % ) group [ relative risk ( RR ) 3.1 , 95 % confidence interval ( CI ) 1.6 to 6.2 ; RR 4.2 , 95 % CI 1.9 to 9.4 , respectively ] .