* Part 1 - Pre-menarche monitoring ("holding pattern"):
Inclusion Criteria:
* Age 8-14.5 years old
* Healthy weight, defined as having a body weight \>85% of expected (EBW) and a body mass index (BMI) \<99th percentile
* Some breast development
* Pre-menarche
Exclusion Criteria:
* Taking or planning to take medications that affect reproductive hormones in the next 2 to 3 years (e.g. birth control pills, biotin supplements).
* Planning to move more than 60 miles from the CRU within the next 2 to 3 years
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* First-degree relative with polycystic ovarian syndrome, premature ovarian insufficiency, hypogonadotropic hypogonadism, or other pubertal development disorder
* Excessive exercise (defined as running \>20 miles per week or its equivalent)
* Pregnancy
Part 2 - Post-menarche cycle tracking:
Inclusion Criteria:
* Age at menarche 10-14.5 years old
* Healthy weight, defined as having a body weight \>85% of expected (EBW) and a body mass index (BMI) \<99th percentile
* Approximately \< 6 months post-menarchal (will typically have completed 4 or fewer menstrual cycles)
* Biochemical criteria: normal thyroid hormone, prolactin, and testosterone levels
Exclusion Criteria:
* Taking or planning to take medications that affect reproductive hormones in the next 2 to 3 years (e.g. birth control pills, biotin supplements).
* Planning to move more than 60 miles from the CRU within the next 2 to 3 years
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* First-degree relative with polycystic ovarian syndrome, premature ovarian insufficiency, hypogonadotropic hypogonadism, or other pubertal development disorder
* Excessive exercise (defined as running \>20 miles per week or its equivalent)
* Anemia (defined as hemoglobin \<12.0 g/dl)
--Participants with hemoglobin between 11.5 g/dl and 12.0 g/dl may still participate by providing dried blood spots, or no more than 18 ml of blood during any given interval.
* Pregnancy
Part 3 - Intensive monitoring of ovarian follicle growth
Inclusion Criteria:
* Age at menarche 10-14.5 years old
* Healthy weight, defined as having a body weight \>85% of expected (EBW) and a body mass index (BMI) \<99th percentile
* Within 1 year of menarche
* Biochemical criteria: normal thyroid hormone, prolactin, and testosterone levels
Exclusion Criteria:
* Taking or planning to take medications that affect reproductive hormones in the next 1-2 years (e.g. birth control pills, biotin supplements).
* Planning to move more than 60 miles from the CRU within the next year
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* First-degree relative with polycystic ovarian syndrome, premature ovarian insufficiency, hypogonadotropic hypogonadism, or other pubertal development disorder
* Excessive exercise (defined as running \>20 miles per week or its equivalent)
* Anemia (defined as hemoglobin \<12.0 g/dl)
--Participants with hemoglobin between 11.5 g/dl and 12.0 g/dl may still participate by providing dried blood spots, or no more than 18 ml of blood during any given interval.
* Pregnancy
Part 4 - Late Post-menarche cycle tracking:
Inclusion Criteria:
* Age 11-17.5 years old
* Approximately 2-5 years post-menarchal
* Biochemical criteria: normal thyroid hormone and prolactin
Exclusion Criteria:
* Taking or planning to take medications that affect reproductive hormones in the next 2 to 3 years (e.g. birth control pills, biotin supplements).
* Planning to move more than 60 miles from the CRU within the next 6 months
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* Anemia (defined as hemoglobin \<12.0 g/dl)
--Participants with hemoglobin between 11.5 g/dl and 12.0 g/dl may still participate by providing dried blood spots, or no more than 18 ml of blood during any given interval.
* Pregnancy
Adolescent girls, at-risk daughters, or sisters of women with PCOS
The girls with mothers or sisters with PCOS group will complete the Screening Visit and Parts 1-3. The same inclusion and exclusion criteria apply for Parts 1, 2, and 3 as stated above except that these individuals must have a first-degree relative with PCOS and they can have high androgen levels, excess body hair, and severe acne at screening.
Women with known PCOS (activities for 8 weeks only)
Inclusion Criteria:
* Age \>=18-34 years old
* PCOS diagnosis
* at least 3-years post-menarchal with irregular menstrual cycles
* Biochemical (blood) or clinical signs of high androgen levels
Exclusion Criteria:
* Cannot be taking any medications that affect reproductive or metabolic hormones (e.g. birth control pill, biotin supplements, spironolactone, metformin).
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* Pregnancy
Healthy control women (Activities x 2 menstrual cycles)
Inclusion Criteria:
* Age \>=18-34 years old
* at least 3-years post-menarchal with regular menstrual cycles every 21-35 days
Exclusion Criteria:
* Cannot be taking any medications that affect reproductive or metabolic hormones (e.g. birth control pill, biotin supplements, spironolactone, metformin).
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* PCOS diagnosis or first-degree relative with disorder
* Pregnancy
Mothers of pediatric participants (Activities for 8 weeks / 2 menstrual cycles)
Inclusion Criteria:
* Age \>=18-65 years old
* Biological mother of A Girl's First Period participant
Exclusion Criteria:
* Chronic medical condition, including but not limited to diabetes mellitus, congenital adrenal hyperplasia, cystic fibrosis, sickle cell disease, inflammatory bowel disease, juvenile rheumatoid arthritis, and lupus.
* Pregnancy
