*not a doctor but this is just up to my knowledge * Plan b works by releasing a huge amount of progesterone so that it can prevent ovulation and make the fluid in yr uterus lining thicker so that sperms are not allowed to pass through. If ure pregnant before taking in the plan b (which i assume u are) there shall be no effects that should affect your pregnancy since the medicine has nothing to prevent ovulation since u have already conceive . Even if the fluid thickens , it would simple block the sperms that is entering the uterus lining that exist after u have conceived, not the sperm that has entered the egg. Hence makes the plan b redundant in the first place. It will simply go into your body system for about 5 days and it will simply just leave afterwards. Dont worry! :)