The 4 indicators of fertility & why these are important to know
The 4 indicators of fertility and why these are important to know your fertile window is a specific time frame in your menstrual cycle during which fertilisation can occur. It is approximately 6 days long. For women with a consistent 28-day cycle, this is typically from days 9 to 14. The last day of this fertile window is the day of ovulation.
Why is this important to know? Well if you try to conceive during your fertile window you have a 10-33% chance of becoming pregnant. Outside of your fertile window your chance of becoming pregnant is less than 1%. This means that identifying when the fertile window is can help increase your chances of conception dramatically.
There are 4 ways to help identify when your fertile window is
Cycle length
Basal body temperature
Cervical secretions
Fertility hormones
Tracking your cycle is a great way of identifying your fertile window, 60 % of the time, ovulation occurs within 1 day of the midpoint of your cycle. And 78% of the time, ovulation is within 2 days of the cycle midpoint. Starting to track your cycle is a great way of learning how regular your cycle is, it can also help you understand any trends if you are tracking mood, energy levels, cravings.
Ovulation marks the end of the fertile window, as the your egg can only survive for up to 24 hours after it’s released from an ovary.
The first full day of continuous bleeding marks the commencement of a new menstrual cycle. A cycles end is therefore last day without full bleeding. Completing 3 months of tracking on the many apps now available should be enough to start to recognise a pattern so that you are now able to identify your average mid point.
If your cycle is longer than 30 days I would recommend rather than taking the midpoint, to instead take the end point and minus 14 days. This is because the luteal phase of the cycle can only last 14 days so for cycle lengths longer than 30 days this will probably be more accurate.
While a very easy method, this is only really accurate depending on how regular your cycle is, as it represents a retrospective indicator of fertility.
Next up is your basal body temperature. You see just after ovulation, the corpus luteum starts producing progesterone. This surge in progesterone causes your basal body temperature to increase around 0.2-0.5 ºC, which then remains elevated until the end of your cycle. Again this is another retrospective indicator as the rise comes after ovulation.
It can be worth tracking alongside your cycle to get a more accurate picture of any patterns. Tracking this can increase accuracy in predicting fertile window to 75-90% accuracy. (remember to measure first thing in the morning)
Next up Cervical secretions. While this may not sound that appetising, keeping an eye on cervical mucus is one of the most useful pieces of fertility information to collect in tracking fertility. The properties of your cervical mucus are pivotal because they influence whether sperm cells are capable of surviving and travelling to her fallopian tubes. Having a specific kind of cervical mucus at the time of sexual intercourse can be the difference between a 0% chance of conceiving and a 29-41% chance. Mucus is a prospective indicator of fertility as it is present in the first half of the menstrual cycle.
There are 4 types of mucus, Dry, Damp, Moist and Wet. Wet cervical mucus represents your most fertile point. It is much more difficult for sperm cells to move when there’s sticky ‘moist’ mucus or no mucus at all. So during ovulation, your body switches to producing wet mucus instead. By using cervical mucus data prospectively and retrospectively you can predict when your fertile window is to a 88-96% accuracy.
Finally there are 2 hormones you can track to help pinpoint your fertile window. These are oestrogen and luteinising hormone (LH). This can be more costly but can also be more accurate. At the start of the fertile window, oestrogen levels start to increase (surge) due to the development of the dominant follicle. This then triggers an LH surge, which is reached usually just before ovulation. So the day of an LH and the day after, are typically a woman’s most fertile days since ovulation typically occurs 1 to 2 days after the surge.
At home ovulation testing kits that measure oestrogen and LH may be the best bet as it may give you an earlier indicator of when you start entering your fertile window, also if you can opt for one that is a digital reading as these are usually easier to interpret. (A 2005 study found that testing at lunchtime 11-3pm gave more accurate results).
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