Puberty in girls typically follows a predictable course of thelarche (breast development) to pubarche (pubic hair) to a growth spurt and, finally, menarche.

The follicular phase of the menstrual cycle is marked by rising estrogen levels produced by the enlarging dominant follicle (ie, a large cyst with multiple smaller cysts), resulting in:

• An increase in quantity of cervical mucus, which facilitates the transfer and maturation of sperm for fertilization
• A thickened endometrium in preparation for implantation
• Enlarge adnexa may be appreciated on physical exam especially late follicular phase

Normal U/S→Pelvic ultrasound shows the left ovary with a 3-cm cyst with several subcentimeter cysts in the periphery. There is normal Doppler blood flow with a small amount of free fluid in the posterior cul-de-sac.

A normal menstrual cycle lasts approximately 3 to 8 days and occurs every 24 to 38 days. Light periods do not typically indicate pathology. In patients on oral contraceptive pills, the total duration and volume of a woman’s menstrual cycle may decrease over time. This patient should be reassured that the change in the volume of her menstrual periods is typical and that her menstrual cycles fall within normal parameters.

The first half of the menstrual cycle is referred to as the follicular phase, which begins with menses and is variable in length. During menses, follicle-stimulating hormone and luteinizing hormone (FSH and LH, respectively) concentrations increase and stimulate the developing follicle. The follicle produces estrogen, which leads to proliferation of the endometrium in preparation for implantation of a fertilized ovum. As estrogen rises, a surge occurs, which in turn stimulates a surge in LH that causes ovulation. Immediately following ovulation, the luteal phase begins as the corpus luteum forms. The corpus luteum secretes progesterone to maintain the endometrial lining, but it is also known to increase basal body temperature. Deficiency of progesterone can lead to a luteal phase defect and infertility. If no implantation occurs, the corpus luteum degrades to the corpus albicans and estrogen and progesterone concentrations decrease, causing menstruation.

In general, the first half of the menstrual cycle is referred to as the follicular phase, during which follicle-stimulating hormone and luteinizing hormone (FSH and LH, respectively) concentrations increase and stimulate the developing follicle. This follicle then produces estrogen, which leads to proliferation of the endometrium in preparation for implantation. An LH surge causes ovulation, after which the luteal phase begins, with the corpus luteum secreting progesterone to maintain the endometrial lining. If no implantation occurs, the corpus luteum degrades, estrogen and progesterone decrease, and menstruation occurs. In patients with diminished ovarian reserve, FSH will be increased early in the follicular phase (typically measured on day tients wim aimited ovarian reserve, FSH wil be increased in day 3 of the menstrual cycle), as more hormone is needed to stimulate the remaining follicles, and there is less negative feedback on FSH from the existing follicles.

• The cervical mucus in the late follicular phase (10-14 days after the last menstrual period) and leading up to the point of ovulation is clear, thin elastic, and often perceived by patients as abnormal vaginal discharge (particularly in those who have previously been anovulatory).

Mittelschmerz

• Ovulatory vs non-ovulatory cycles
• The initial menstrual cycles in adolescents are irregular and anovulatory.

<aside> 💡 During the first year after menarche, adolescents often have anovulatory cycles with heavy, irregular menstrual bleeding due to an immature hypothalamic-pituitary axis

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