Hi, thanks for your question. If you mean the emergency contraceptive pill Plan B as the ‘ellaone pill’ your wife took, then this is very effective at preventing pregnancy. There should be a bleed like a period within 21 days of taking the emergency contraceptive pill. this should happen no matter when your wife’s period was expected. If she gets a bleed within 21 days then this means the pill has worked. If there is no bleeding like a period by 21 days, then your wife should take a pregnancy test then. Hope this helps. Health Nurse