After UPSI sperm can survive for approximately 5 days within the female reproductive tract.1 This means that during the average woman’s menstrual cycle there are six days when intercourse can result in pregnancy; this ‘fertile window’ is the five days before ovulation plus the day of ovulation.2
So when is the fertile window? Current evidence challenges the simplified ‘text book’ understanding of the menstrual cycle.2 We now know that only about 12% of ovulations happen on day 14.3
The variability of ovulation is large – it can happen from day 11 to day 21.2 Because sperm stay viable for up to 5 days1, the period over which conception is likely to occur runs from day 6 to day 21 for regularly cycling women.2 If the cycle is not regular, there is a risk of ovulation happening even later in the cycle.2 The conception risk period does not end before day 28 of their cycle.2 This shows that there is no such thing as a risk free period.2
Ovulation also varies from cycle to cycle.2
The highest risk of pregnancy is when ovulation happens shortly after UPSI6
Sperm viability declines over time. This means that the risk of conception is highest during the first three days following unprotected sex or contraceptive failure.6
Therefore, to avoid unwanted pregnancy, it is critical to avoid ovulation (happening shortly after UPSI while the sperm is still viable) by using EC as soon as possible.
