Based on the information on the previous pages, it is clear that pinpointing each woman’s dates of fertility can be very subjective. While there are certain guidelines that can be followed in order to create a fertility chart, each woman’s chart will be unique and has the potential to shift and change due to irregularities in the menstrual cycle.
Fertility Guidelines:
- Cycles vary from month to month, therefore an average should be taken of each woman’s shortest cycle and her longest cycle (this means fertility should be charted at least twice).
- Ovulation generally occurs 14 days before the last day of the menstrual cycle
- Because this is a general statement, it is necessary to account for discrepancies using a margin of error of two days earlier and two days later than estimated ovulation.
- An egg can live in a woman’s body for up to 24 hours (1 day).
- Sperm can live in a woman’s body for up to 3 days.
Basic fertility chart:
| First day of cycle | Last day of cycle | |||||
| (First day of menses) | -3: Life of sperm (3 days) | -2: Margin of error | Ovulation -14 days | +2 Margin of error | +1: Life of egg (1 day) |
This calculation is important for general awareness, and can be used for planning pregnancies, but is most commonly used at the SHPRC to calculate whether or not there is a need for Emergency Contraception
EXAMPLE:A woman comes in worrying that she might be pregnant after a condom broke last night. Her longest cycle is 31 days, her shortest cycle is 26 days. Her period started (and thus her cycle began) 10 days before her possible conception last night.
Shortest Cycle = 26 Days
Day 1--------------------7------------10--------12--------14----15---------------Day 26
Longest Cycle = 31 Days
Day 1------------------------------------------12------------15--------17-------19-----20-------------------Day 31
Potential Days of Fertility = from Day 7 to Day 20
Significance: The potential period of fertility includes the date of possible conception, Day 10. The woman should consider using Emergency Contraception and be referred upstairs.
Conclusion: Fertility charting can also be used as a contraceptive technique known as “Natural Family Planning.” There will be more information on Natural Family Planning in the contraception chapter of the course reader. Fertility charting can be made more specific depending on how well a woman knows her own body, or how willing she is to chart specific aspects of her cycle and changes in her body.