Ovral Emergency: Is Only one dose enough?

Patient: Hi, I started my period the evening of Feb 21st and it ended on Thursday Feb 22nd. I had unprotected sex today and there was ejaculation in my vagina. Could I get pregnant? I had only one dose of Ovral Emergency contraception so I took only one pill a few hours after and will take the other one 12 hours later. Do i absolutely need to have 2 pills at each time? Thank you

Doctor: I understand your concern about possible pregnancy.  According the first day of your last menses, the day you had unprot tected sex will be the 11th, this could be considered one of the dangerous days because of its proximity to ovulation, especially if you are regular.The problem with taking only half the dose is that the hormone concentration might not be enough, 2 pills taken 12 hours after the other 2 pills is necessary.If you are still within 72 hours of conception, you might want to try emergency contraception again, remember to do it correctly this time to ensure better efficacy. I wish you the best.