It depends kung kelan mo ininom.. usually nagtetake ng pills 1st day ng period mo.. kung meron ka pa and ginawa niyo.. wala pong chance mabuntis.. pero kung ininom niyo yung pills ng hindi pa nagkakaroon.. may chance po na mabuntis.. since around 3 days bago magtake effect yung pills.. kaya po inaadvise ng OB to use other contraceptive kung kakastart pa lang uminom ng pills😊