Reproductive System: Follicular Phase

We previously explored the uterus as a muscle that prepares for childbirth. Now, let’s focus on specific phases of the reproductive cycle and talk about the beginning of reproduction as we work to fully understand the childbearing years. Women have two ovaries near the top of their uterus that hold all the immature eggs (follicles) she will ever have. These follicles were created when she was a baby inside of her mother’s uterus. Each follicle must mature (which appear as cysts) for conception to be possible. When a woman is mature enough for her hormones to start this rhythm, she begins the Follicular Phase of her cycle.

If you are already menstruating, the Follicular Phase begins on the first day of your period; however, the Follicular Phase actually occurs before you ever have a period (such as your very first or when your cycle returns after postpartum or other times of no period).

During the Follicular Phase, multiple follicles (not just one) should begin to mature in both ovaries. If you have optimal balance in your body, FSH (Follicle Stimulating Hormone) increases, stimulating multiple follicles (cysts) to mature and be ready for conception. Each of these follicles will mature at different rates. Ideally, 5-7 days after the Follicular Phase begins, one follicle will reach optimal maturity, causing the other maturing follicles to dissolve. This triggers the body to increase Estradiol (E2, our main type of Estrogen) production, which starts thickening the endometrial lining of the uterus, to allow a fertilized egg to implant into it later in the luteal phase of the cycle.

If you are already menstruating, you will notice that a previously healthy cycle will contribute to how you experience your period and the Follicular Phase.  If progesterone was imbalanced with estrogen, bleeding and discomfort may be imbalanced, the Follicular Phase may be altered.  Your immune system does play a role in your period, and you need to begin this part of your cycle with low levels of both Progesterone and E2.  We’ll talk more about this in a later newsletter, but for now we need to understand that if E2 starts too high, FSH may not get the signal to increase, or estrogen will increase too much as FSH rises during this phase.  If FSH does not increase high enough, then E2 won’t increase, which is even more problematic when your E2 levels are already too low.  Low E2 and/or low FSH levels can cause late ovulation, or no ovulation (anovulation).  Along with your immune system, rising FSH and E2 helps tell your body when it is time for your period to end.  So, low levels of these hormones (along with a low-functioning immune system) may cause excessive, and painful, bleeding.

Balance is required in your body for the follicular phase to occur optimally, whether this is your first, or 50th, cycle.  The Follicular Phase is stimulated by your lifestyle in the 3-12 months prior to these follicles maturing.   If you’re low in micronutrients from undereating, or not eating a nutrient-dense diet, these hormones likely won’t rise high enough or quickly enough, delaying or preventing ovulation.  If you have a high toxin load, are dehydrated, or have imbalanced stress, this may also delay or stop ovulation, or make this time unnecessarily uncomfortable for you.  If you have underlying gut-health imbalances or stealth infections, this may also delay, or stop, follicles from being stimulated.  All these processes work together and the longer you live a balanced and optimal lifestyle, the more balanced your cycle will become.


On Day 3, serum blood labs can tell us if we see a slight increase in FSH and E2, with E2 not yet high.  Additionally, FSH should not be too high because we want FSH to “whisper” to Estradiol (E2). If it has to “yell” for Estradiol to rise, you may experience a late or anovulatory cycle (or may be peri-menopausal).  Progesterone should have dramatically dropped, be low, and allowing E2 to rise.  LH should be low, but it should be a near 1:1 ratio to FSH.  Testosterone & SHBG should be present, but in moderate amounts. If any of these hormones at this stage are elevated, it may indicate PCOS (not an ultrasound that shows multiple "cycts" i.e., maturing follicles - PCOS cannot be diagnosed with ultrasound alone).

Day 3 Optimal Blood/Serum Values

  •   FSH: 2.5-6.0 mIU/L
  •   Estradiol E2: 30-50 pg/mL
  •   Progesterone: <1.5 ng/mL
  •   LH: 1.5-3.15 mIU/L
  •   LH/FSH Ratio: 1:1
  •   Testosterone Total: 30-55 ng/dL
  •   Testosterone Free: 2-4.2 ng/dL
  •   SHBG: 50-80 nmol/L

DUTCH urine/saliva ranges are different.


Interested in exploring hormones and cycle balance?  Reach out at for a wellness visit and root-cause testing.