Family Planning Plus

If your girlfriend was on the pill for at least one full week before the encounter occurred and as long as she has not missed any of her pills, there is no need to take Plan B.  It will probably just make her nauseous (since she will be overloading her system with hormones) and cause her next period to be irregular.  The pill is close to 99% effective with perfect use (provided she is taking her pills at the same time every single day and as long as she is not using any medication that would lower the pill’s effectiveness). 

A woman is most fertile around the time of ovulation.  Ovulation typically occurs about two weeks prior to the beginning of the menstrual period.  A woman’s monthly cycle is measured from the first day of her menstrual period (Day 1) until the first day of her next period. On average, a woman’s cycle normally is between 28-32 days, but some women may have shorter or longer cycles.  Each woman is different.  Most women ovulate anywhere between Day 11 – Day 21 of their cycle, counting from the first day of the LMP.  This is what many refer to as the “fertile time” of a woman’s cycle, because sexual intercourse during this time increases the chance of pregnancy.   There are tools available to chart the time of ovulation.  Google CM-BBT.