In this article, we review two methods that have been used to identify the fertile window: basal body temperature monitoring and LH hormone monitoring.
All methods used to track ovulation can be classified as prospective or retrospective methods:
- prospective methods rely on events that happen before ovulation and indicate the presence or absence of a follicle developing, oestrogen dominance and/or LH surge;
- retrospective methods rely on events that happen after ovulation and indicate the presence of a corpus luteum with progesterone dominance.
If you are trying to conceive, a method that identifies ovulation before it happens is more useful as once ovulation has occurred, you only have a few more hours to get pregnant.
Tracking Basal Body Temperature
Monitoring of basal body temperature has been widely used and is one of the simplest and least invasive methods to detect ovulation. This method relies on a woman measuring her temperature every morning before any activity. It can be most commonly measured orally, rectally, and vaginally.
The temperature fluctuates due to hormonal variations in the menstrual cycle. During the follicular phase of the menstrual cycle, the temperature is lower, until approximately one day before ovulation, when it reaches its lowest point (called nadir). After ovulation, the corpus luteum begins to secrete progesterone: the temperature increases and plateaus throughout the luteal phase. In the late luteal phase, when the corpus luteum regresses and serum progesterone level decreases, the temperature returns to the lower range within 1 or 2 days before, or just at, the onset of menstrual bleeding.
Because one cannot identify the lowest temperature point until the subsequent rise is seen, it means we can only see if ovulation has occurred, after it has happened. For this reason, tracking basal body temperature is a retrospective method.
As this method only indicates ovulation once it has already happened, basal body temperature is not the most appropriate method to time sex to achieve a pregnancy. If your cycles are very regular, some algorithms may predict the next ovulation with some degree of certainty, but it is never certain until it actually happens.
Apart from this fact, other factors can influence temperature or present some challenges to the basal body temperature method to detect ovulation:
- It requires a high degree of compliance, as you need to measure the temperature every morning around the same time and before you do any activity.
- You need to interpret the chart to learn that ovulation has happened. A significant increase is at least 0,2°C that lasts for three days or more is a sign that ovulation has occurred.
- Account for several factors that can affect the temperature readings, like consumption of alcohol, oversleeping, the difference in time zones, shift work, stress, change in room temperature, change of climate, illness, and medications.
For all these reasons, monitoring temperature is not the most effective method to identify your fertile window. In fact, a review article published in 2005 concluded that monitoring basal body temperature was no longer a good predictor of ovulation and, therefore, should not be recommended for couples seeking pregnancy. Even though it’s not a good indicator to predict ovulation, monitoring temperature can be effective as a sign of pregnancy: when the temperature rises in relation to ovulation and lasts 18 or more days, it can be an early indicator of pregnancy.
Tracking Luteinizing Hormone (LH)
When serum estradiol concentration (secreted by the follicles) reaches a threshold level, a positive feedback mechanism works on the hypothalamus and anterior pituitary gland, which results in an abrupt secretion of LH into the bloodstream.
The onset of the LH surge precedes ovulation by 35–44 hr, and the peak serum level of LH precedes ovulation by 10–12 hours. It usually occurs between midnight and early morning.
This marks the most fertile period of the menstrual cycle. Because this happens before ovulation, this is a prospective method that can detect ovulation ahead of time, giving you 24-48h for timed intercourse before ovulation.
The best way to track LH is through urine sticks like myLotus. The monitor will keep a record of your values and indicate when you start your fertile window. This is especially useful if you have irregular cycles.
There are several methods that you can use to track ovulation, but the best methods are the ones that tell you when ovulation is happening ahead of time, giving you the best chances of timing sex for conception. Choosing a prospective method like LH monitoring is more likely to provide you with an accurate result and increase your chances of natural conception.
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