Effectiveness of Plan B during ovulation

Dear Ask The Doctor: I'm a little worried that the Plan B One-Step may not work. Recently during intercourse (july17 at 1am) the condom broke. My last period began on July 5 and ended on July 9. I took plan b within 45 Min after intercourse but keep reading that if I was already ovulating Plan B will not work. My prior period was around June 9and also lasted 5 days. Based on my calculations I may have been ovulation on July 17. Any advice to potentially ease my mind or help me prepare would be great.

Dear Kelly: Plan B works through different mechanisms including,

- delaying or preventing ovulation,

- interfering with fertilization (inhibiting the movement of the egg or the sperm through the fallopian tube) and

- may inhibit implantation by altering the lining of the uterus.

Thus Plan B may be effective irrespective of ovulation, however if the process of implantation has already begun, this contraception may not be effective.