Treatment to prevent sexually transmitted infection is available, and there are resources available to provide emotional support. To make an informed decision regarding the need for emergency contraception, it helps to have an understanding of the normal menstrual cycle and its relationship to fertility. Although it s never advisable to have unprotected intercourse unless pregnancy is desired, the degree of pregnancy risk depends on where you are in the menstrual cycle. Most women have a period every 26-35 days. It is normal for a menstrual cycle to vary slightly in length from month to month.
Menstrual cycles have two phases.
The first phase may vary from 13-20 days in length and ends when ovulation occurs. This phase varies from one woman to another and may also differ slightly from month to month. The second phase is about the same length in all women. Generally, after ovulation occurs, the menses will start in 14 days. For the sake of simplicity, we will use a 28-day cycle to explain the pattern of ovulation.