The fertile window results from a sequence of hormonal changes orchestrated by the hypothalamic-pituitary-ovarian (HPO) axis. At the start of your cycle, or the first day of your period, the rising FSH, produced by the pituitary gland in the brain, drives the ovarian follicles to begin to grow.
The importance of estrogen should not be undermined. While working to develop the lining of the uterus, the peak in estrogen also facilitates the trigger the surge of luteinizing hormone, or LH-the hormone detected by ovulation predictor kits. This rise in LH then triggers the release of the egg from the dominant follicle. The rise in LH can be brief, or can be sustained and remain elevated even after ovulation has occurred.
So, when does the fertile window fall during this rhythmic sequence of hormonal changes?
To answer this, we first need to understand the role of cervical fluid. Cervical fluid makes the vaginal environment a sperm-friendly place to be. As estrogen rises and the chemical composition of the fluid also changes, the pH lowers which is vital to the survival of sperm. In addition, the increasing quantity of mucus helps create channels from which to filter out abnormal sperm and support typical sperm on their journey towards the egg. The cervical fluid also provides vital nutrients to sustain and nourish the sperm while they await the release of the sperm. Given all of these ways that the cervical fluid supports the sperm, the sperm can survive in the reproductive tract for up to 5 days.
Let’s put the pieces together.
Since sperm can survive for up to 5 days thanks to the nourishing and hospitable vaginal environment that the cervical fluid creates, the fertile window extends for about 5 days. For most, ovulation occurs within 24-36 hours after the LH surge, however, it can range from 12-48 hours.
With kegg, the user is able to see the full fertile window. We recommend timing your efforts throughout the full fertile window. If a woman relies on LH testing alone, she likely will miss the 3-4 days before the rise in LH that are fertile, and have a high probability of conception. This means, while the cervical fluid is hospitable to sperm, as reflected in the valley, the LH test will be negative.
Let’s compare the LH surge relative to kegg’s fertile window in this kegg chart.
If this user had waited for her LH surge to time her trying to conceive efforts, she would have likely had one day to time her efforts in her fertile window. Thankfully, she was able to see her full fertile valley to optimally time her efforts throughout her fertile valley with kegg.
While tracking LH can be useful for being aware that ovulation may be imminent, it fails to properly identify the fertile window. A negative LH test does not ensure that the user is not in their fertile window. Conversely, a positive LH test does not guarantee the user is in the fertile window. As a result, relying on LH testing to time your trying to conceive efforts will not assist in optimally timing your trying to conceive efforts. Thankfully, kegg takes the guesswork out of timing for you so you can ensure you do not miss an opportunity to conceive.