GenderLabs™ v1.3 applies Fertility Awareness Method (FAM) principles as the basis to determine the date limits for fertility and infertility periods. Setting the start date of one phase automatically determines the end date of the previous phase. The start date for Phase 1 low fertility is set based upon menstruation. Phase 2 fertility is set based upon the presence of Cervical Mucus (CM) or using a formula based upon shortest historical cycle length. The start of Phase 3 infertility is set based upon temperature changes alone or a combination of temperature and CM changes.

In understanding how GenderLabs™ v1.3 predicts fertility, it's helpful to review the fertility cycle again:

Obviously, there is no real need to set the end date for any particular phase, as it is automatically set when you set the start date for the next phase. GenderLabs™  uses the symptoms of menstruation, CM and Basal Body Temperature (BBT) to set these start dates.

Determining the Start of Phase 1 Infertility

Setting the start date of Phase 1 is easy -- it's the first day of menstruation. Phase 1 is said to be infertile, but as you get near the end of it, it becomes slightly more fertile. This is due to its closeness to ovulation and the fact that sexual relations before ovulation that most frequently result in pregnancy. The ovum only survives about 24 hours on its own, so sexual relations which take place 24 hours after ovulation don't normally result in conception. However, sexual relations as many as 5 days before ovulation may result in conception.

For this reason, it is very important to set the start of Phase 2 fertility accurately.

Determining the Start of Phase 2 Fertility

If you recall from our discussion of the clues to fertility, CM is a positive sign of fertility. This means that the start of the fertile period, Phase 2, is set on the first day and CM appears. This is because CMallows sperm to live up to 5 days, which means that ovulation doesn't have to occur just after sexual relations for a woman to conceive a child. On the other hand, without cervical fluid, sexual relations do not normally result in conception (we say "normally" because even though it's highly unlikely, anything is possible!) Therefore, GenderLabs™  treats the start of fertility, Phase 2, as being the first day CM is present.

What if you're not tracking CMand have decided to use menstruation and basal body temperature as your only symptoms? Or what if you normally do use CMbut for whatever reason, you fail to do so in the current cycle? GenderLabs™  will treat cycle day 6 as the start of the fertile phase in such a situation.

GenderLabs™, however, will also review your prior cycle history and will allow you to override CM observations if your cycle history suggests that you are truly infertile.

A Note about Cervical Mucus (CM) Changes as Ovulation Approaches

CM first appears during Phase 2 and changes in quantity, color and consistency as ovulation approaches. The "less fertile" type of CM is typically sticky, crumbly or creamy/opaque, the "more fertile" type is like raw eggwhite (wet, stretchy, slippery, and clear)

Armed with this knowledge, pregnancy achievers can be fairly certain when their chances for conception are highest. Just after ovulation, the hormone progesterone is released and estrogen levels drop, causing CM to begin "drying up" -- it goes from the more fertile to a less fertile type. The first day of this change, fertility and conception chances are still high. Within a day, the conception chances drop considerably, so sexual relations are advised through this period to achieve pregnancy.

Determining the Start of Phase 3 / Post-ovulation Infertility

The start date for Phase 3 infertility can be set based on temperature changes alone, or better yet, based on a combination of temperature changes and changes in CM characteristics.

FAM requires there to be a significant upward shift in basal body temperatures for at least three consecutive days over the previous six days. All temperatures must be undisturbed by late rising, sickness, physical exertion, etc. This again points to the value of taking your temperature the FIRST thing in the morning, as there is less chance that these readings will be disturbed.

What determines whether a rise in temperature is significant? FAM uses a number of rules for determining whether this condition has been met. First, a coverline is drawn 0.1° F (0.05° C) above the highest of the six pre-shift temperatures. Once 3 or more temperatures are above the coverline, a thermal shift is said to have taken place.

While it goes beyond the scope of this section to explain it in details, BBT rises are categorized as follows:-

Standard Thermal Shift: Three successive days with temperatures above the coverline.

Slow-rise Thermal Shift: The first temperature in the shift is at the coverline; the remaining temperatures are above the coverline. Requires four successive days with temperatures above the coverline.

Fall-back Thermal Shift: The first temperature is above the coverline, the second dips back to or below the coverline, followed by three temperatures above the coverline. The first temperature might also be eliminated using the Rule of Thumb, which would then make this shift mimic the Standard Thermal Shift.

Once in Phase 3, you are infertile through Phase 1, so you may elect to stop observing your BBT and CM until menstruation starts. However, GenderLabs™ recommends you to continue taking BBT especially if you are anew user, as a matter as good practice. Both observations should be resumed in Phase 1 right after days of heavy menstrual flow have subsided.