I was doing some reading recently and came across some stories of women who had experienced failure of emergency contraception i.e. they still got pregnant despite taking the contraceptive pill within 72hours of unprotected intercourse.

I decided to do some extra digging and got to find out that there is actually a time frame during which Plan B a.k.a Morning after pills fail. This time frame is when a woman is most fertile which is when she is ovulating.

It turns out that emergency contraception often works by delaying ovulation, therefore if a woman just started or just finished ovulating the pill would be rendered ineffective. Although these pills sometimes work by preventing fertilization or implantation of an egg, they are most effective at preventing ovulation.

The importance of this article is to enlighten women, and point out that morning after pills are not a reliable method of contraception and in a situation where one has to fall back on it, its very important to be aware of your ovulation date and avoid intercourse on those fertile days because the pills are likely to fail.

https://www.bustle.com/p/does-the-morning-after-pill-always-work-theres-one-time-of-month-when-it-doesnt-9069768