In the first phase of the menstrual cycle, the follicular phase starts with your period and ends with ovulation. During this phase, your body is preparing for ovulation. This means there’s an increase in hormones that initiate ovulation.
It’s during this phase that the Natural Cycles app may prompt you to take an LH test (also known as an ovulation test). LH tests measure the surge of luteinizing hormones in urine. The presence of this hormone indicates that you may ovulate within the coming 48 hours. Find out more about LH tests here.
Later in the follicular phase, levels of the hormone estrogen increase. This causes the lining of the uterus (or endometrium) to thicken in preparation for the implantation of a fertilized egg cell. At the same time, the rise in estrogen also causes an increase in cervical mucus, this promotes sperm survival and also makes it easier for the sperm to travel up the fallopian tubes.
How long is the follicular phase?
Since all our cycles are unique, the length of the follicular phase varies from woman to woman. Our recent 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. While all of us will experience some irregularities from time to time, those with irregular cycles may expect to see a variation in both the follicular phase and the luteal phase from cycle to cycle.
If you’re curious about your own cycle phases, you can see this individualized data in the "my cycle" tab. Here you can compare your cycles, or take a look at the breakdown of the average length and variation of your own cycle phases.