Follicular Phase

The follicular phase is the first half of the menstrual cycle. It begins on the first day of the period and ends at ovulation. Two hormones drive this phase: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). They recruit follicles in the ovary and help them mature. One leading follicle (the dominant follicle) produces a rising amount of estradiol. Estradiol builds the endometrium, the lining of the uterus. It also triggers the LH surge that causes ovulation.

The length of the follicular phase varies widely from cycle to cycle. The length of the luteal phase varies much less. It holds to a fairly narrow range of 11 to 16 days. For this reason, most of the variation in total cycle length comes from the follicular phase.

This variation explains why calendar-based estimates of ovulation fail. Direct observation of body signs (biomarkers) in each cycle identifies ovulation accurately, on whatever day it occurs.

Restorative Reproductive Medicine examines this phase closely. NaProTECHNOLOGY and FEMM clinicians track cervical mucus observations, serial hormone tests, and follicle ultrasound scans. They use these findings to identify follicular phase deficiency.

Follicular phase deficiency is a phase that is short or low in estrogen, or follicles that do not mature well. It is a distinct problem, and it is often missed. It is the counterpart of luteal phase defect, found in the first half of the cycle. Depending on what testing finds, NaProTechnology protocols may include ovulation induction or estradiol support for follicular phase defect.