The follicular phase is the first phase of your cycle.
It begins on the first day of your period and ends when you ovulate. During this phase, there’s an increase in luteinizing hormone and estrogen as your body is preparing for ovulation.
What happens during the follicular phase?
- Your period occurs: Your cycle starts with menstruation, where your body sheds the lining of the uterus from the previous cycle.
- Temperatures remain low: Temperatures will remain generally below the cover line. Once ovulation occurs, a rise in progesterone causes your body temperature to shift higher, signaling the end of the follicular phase and the start of the luteal phase.
-
Estrogen levels rise: As your body prepares an egg for release, estrogen levels gradually increase. This causes:
- The uterine lining to thicken in preparation for the implantation of a fertilized egg cell.
- An increase in cervical mucus, which helps sperm survive and travel up the fallopian tubes.
- Luteinizing Hormone (LH) surges: Roughly 48 hours before ovulation, your body experiences a rise in LH. An increase in LH levels can indicate that you may ovulate within the next 48 hours. While an increased LH is a strong indication that ovulation may soon happen, it is not a confirmation that ovulation has or will occur.
During the follicular phase, the Natural Cycles app may prompt you to take ovulation tests (also known as LH tests), which measure levels of the luteinizing hormone in the urine. These tests are optional and not required by the algorithm, but when used, they can help the algorithm narrow down your fertile window.
You can read more about using ovulation tests in this article: Why should I take ovulation tests?
How long does the follicular phase last?
Our study of 600,000 cycles found that, typically, the follicular phase is the longest phase of the menstrual cycle and is, on average, 17 days long. However, since all our cycles are unique, the length of the follicular phase varies from person to person.
The follicular phase is naturally the most variable phase of the menstrual cycle, meaning it is normal for its length to shift slightly from month to month.
While everyone will experience some irregularities from time to time, those with irregular cycles can expect to see variation in both the follicular phase and the luteal phase from cycle to cycle.
How to check your follicular phase length in the app
You can see your personal phase data directly inside the Natural Cycles app:
- Open the Today view.
- Scroll down to See Cycle Insights.
- Select Follicular phase.