Women’s reproductive system as balanced estradiol and progesterone actions—a revolutionary, paradigm-shifting concept in women’s health

The influence of the menstrual cycle on muscle injuries - a systematic review and meta-analysis

Guthardt Y et al., 2026 · Sci Rep · Free full text on PubMed Central

This systematic review and meta-analysis examined the relationship between menstrual cycle phases and the incidence of muscle injuries in female team sport athletes, following PRISMA 2020 and PERSiST guidelines. A comprehensive search was conducted in PubMed, Scopus, and SPORTDiscus from inception to mid-January 2024. Studies were included if they examined female team sport athletes of reproductive age with regular menstrual cycles and compared the occurrence of muscle injuries across at least two menstrual phases. Studies involving hormonal contraceptive use, medications affecting the menstrual cycle or musculoskeletal system, or menstrual dysfunction were excluded. Three studies met the inclusion criteria, involving 318 participants. Meta-analysis yielded a pooled Risk Ratio of 1.18 (95% CI: 0.75 to 1.86, p = 0.46) for injury risk between the luteal and follicular phases, suggesting no statistically significant association. However, the certainty of the cumulative evidence was rated as very low due to methodological limitations, including inconsistent phase classifications and reliance on imprecise methods for identifying menstrual phases. Consequently, no practical or clinical recommendations can be made at this time. Future research employing standardised, physiologically accurate methods for classifying and detecting menstrual cycle phases is necessary to better understand the potential links between hormonal fluctuations and injury risk.

MON-154 Breast areolar diameter in healthy menstruating women—a single cycle cross-sectional study of associations with body size and ovulatory characteristics

Baaske AV et al., 2025 · Journal of the Endocrine Society · Free full text on PubMed Central

Tanner Breast Stage 3 (TB3, at menarche) and Tanner 5 (TB5, once ovulatory cycles established), despite being similar with an “upstanding” nipple, are different. Evidence suggests that steady and high ovulatory-level progesterone exposure accounts for the larger areolar diameter in TB5. Progesterone levels indicate whether the menstrual cycle is ovulatory and have crucial implications for women’s reproductive, metabolic, cardiovascular, and bone health. However, few data show average areolar diameter in regularly cycling women in whom SES, body size, and reproductive variables have been documented. As a step towards better understanding the role of areolar diameter in reflecting estradiol-progesterone balance, this study aims to document the average mean bilateral lateral areolar diameter (AD) in a cohort of regularly menstruating, premenopausal women in whom ovulation was documented in one cycle. We also aim to describe relationships between AD and demographic, anthropometric, and reproductive/ovulation variables. Women were eligible if aged 19-35 years with about month-apart cycles and no exogenous hormone use in the last 3-months. Participants completed one cycle with a daily Menstrual Cycle Diary© (cycle length, CL) and first morning temperatures for Quantitative Basal Temperature© (QBT©) ovulation analysis (normal luteal phase length ≥10 days). Questionnaires gathered SES, ethnic, general health, and reproductive characteristics. Bilateral horizontal areolar diameters were measured by a woman researcher with the participant supine in a warm room. From February 2020 to September 2022 (during the SARS-CoV-2 pandemic), 73 women from Metro Vancouver, British Columbia participated. Women were of median (min-max) age 30 (19-35) years, BMI 24.5 (17.1-41.4) and most identified as White (61.6%) with a median of 16 years of education. Median CL was 29 days (n=65) and QBT data showed 39.3% were normally ovulatory, 34.4% had short luteal phases and 26.2% were anovulatory. Median within-woman bilateral AD was 3.85 (2.35-8.00) cm. Left AD exceeded right (L 3.8 [2.3,8.2]; R 3.7 [ 2.4,7.8]; P=.003). Larger AD (≥3.85cm) was associated with greater body size (BMI r=.534), weight and waist circumference. However, earlier age at menarche (P=.02) was also significantly associated. No other reproductive variables (cycle length, luteal phase length, parity, ever use of CHC) were related to AD before body size adjustments. This study is the first to document, and describe demographic, anthropomorphic and reproductive associations with, AD in community dwelling, regularly cycling, premenopausal women. Future steps will determine the most influential of the anthropometric variables; adjustment for these will facilitate assessments of associations with ovulation related characteristics.

SAT-128 Prospective 1-year Menstrual CycleBreast Tenderness and Swelling Experiences—data from healthy regularly cycling women initially proven normally ovulatory on two consecutive cycles

Wood M et al., 2025 · Journal of the Endocrine Society · Free full text on PubMed Central

Breast tenderness and swelling are associated with premenstrual symptoms but have not been well described in healthy, normally cycling women with known ovulatory status. There are documented negative health risks (in bone, the cardiovascular system and cancers) in association with ovulatory disturbances within normal-length cycles. Identifying breast changes across a predictable, month-apart cycle but with Subclinical Ovulatory Disturbances (SOD, short luteal phase [<10 days] and anovulation (with normal estradiol but lower or absent progesterone levels) could advance our understanding of menstrual cycle physiology, women’s health education and identification of those with chronic SOD who may benefit from cyclic progesterone therapy. Our objective was to determine whether within-woman breast tenderness and swelling experiences differed between normally ovulatory and ovulatory-disturbed cycles. In this 1-year prospective observational study, we examined daily breast tenderness (0-4) and swelling (1-5 change from usual = 3) experiences recorded via the Menstrual Cycle Diary© over ≥8 cycles (mean=13/woman) in 53 women. Ovulatory status was documented by the twice-validated Quantitative Basal Temperature© (QBT©) analysis. Cycle and ovulatory data were previously reported (Prior NEJM, 1990); Diary data were unreported. Participants were healthy, community-dwelling women, mean age 34 (32.4:35.5 years), BMI 22.0, primarily White, and about two-thirds were runners (for health or were marathon-training). Comparison of breast parameters in all normally ovulatory (n = 495) vs all SOD cycles (n = 199) (mean cycle length 28.1 [27.5-28.8 days]), showed significantly higher Breast Tenderness Score [intensity X days; 6.0 (range 1.0, 14.0) vs. 3.0 (0.0, 11.0) (P = .001)] and increased breast size [4.0 (2.0, 4.0) vs. 4.0 (0.0, 4.0) (P = .034]) in normally ovulatory cycles. However, in within-woman analysis (n = 47 women with both normally ovulatory and SOD cycles), breast tenderness/swelling did not significantly differ by ovulatory status. We plotted all ovulatory cycles (n=676) centred on ovulation; this revealed parallel timing of increases in breast tenderness and swelling in the late luteal phase. These 1-year prospective data documented that mild breast tenderness and swelling occurred before flow in cycles with normal ovulation; symptoms were less in SOD cycles. Breast changes were totally absent during the follicular phases.

"SUN-109 Feasibility of Cyclic Progesterone and Spironolactone for PCOS-specific Health-Related Quality of Life—a six-month, Phase II, single arm, single center, open-label study"

Nelson K et al., 2025 · J Endocr Soc · Free full text on PubMed Central

Polycystic ovary syndrome (PCOS) is an endocrine-metabolic disorder that significantly decreases health-related quality of life (HRQoL). Combined hormonal contraceptives (CHC) are standard-of-care for PCOS but do not mitigate the neuroendocrine cause nor women’s primary concerns. Treatment options need expansion. We hypothesized cyclic oral micronized progesterone (CyclicP4) and spironolactone (Sp) would improve HRQoL, decrease LH, and acne. This Phase II, open-label single-arm pilot study evaluated the 6-month cyclicP4 and Sp treatment feasibility and safety in androgenic PCOS. Our primary outcome was within-woman change in PCOS-HRQoL (PCOSQ). No sample size calculation was possible; 40 was considered feasible. Eligible women were 19-40 years with physician-diagnosed androgenic PCOS. Exclusion criteria included HbA1c > 6.4%, use of metformin or CHC in the last month. Participants received progesterone (300 mg/bedtime 14 days/month); spironolactone (200 mg/day) began in cycle two. Adherence was tracked daily (Menstrual Cycle Diary©) and by pill counts. Safety was assessed by post-study potassium (K+). Feasibility by women’s post-trial treatment intention. PCOSQ, serum LH, calculated bioavailable testosterone (cBAT), HbA1c, hsCRP, and AMH were measured at baseline and trial end. We also assessed perceived acne and sleep changes (-5 to +5), K+ and therapy intent at study end. Six-month change by paired t-test or Wilcoxon signed-rank assessed P < .05 as important. Of 109 expressing interest, 41 enrolled, 36 began therapy (5 did not), and 26 provided final questionnaire data (19 with complete lab data). Completing women were mean age 29 (SD 4.9) years, BMI 30.3 (8.1), 61.5% White and 73.1% with university degrees. Total PCOSQ scores within-woman increased from 3.5±1.0 to 4.9±1.1 (95% CI 3.1-3.8, 4.6-5.3; P<.0000001). Each PCOSQ domain significantly improved (at least P<.001) as did acne and sleep. Weight was unchanged but waist circumference decreased 1.1 cm (NS). LH, cBAT, and AMH each decreased: LH 10.0±5.4 to 8.5±5.2 IU/L (95% CI 7.6-12.3, 6.3-10.8; P<.4), cBAT 0.7±0.4 to 0.6±0.3 nmol/L (0.5-0.9, 0.5-0.8; P<.2), and AMH 10.5±6.5 to 9.7±5.7 ng/ml (7.4-13.7, 7.0-12.4; P<.4). hsCRP remained unchanged (2.8±3.3 to 2.7±3.6 mg/L; P<.8) as did HbA1c (5.2±0.3 to 5.2±0.3%; P<.0). K+ remained within the normal range (3.5-5.0 mmol/L) at final testing (mean 4.0). Two allergic responses to spironolactone and one frequent flow/religious practice led to discontinuation. Feasibility was confirmed and participants strongly preferred continuing therapy (median Likert score=6/7, P<.0001) CyclicP4 and Sp for 6-months was feasible and significantly improved HRQoL in a non-medicine-seeking community women cohort with androgenic PCOS. Though the small sample size limited generalizability, findings are promising. A larger randomized trial comparing CyclicP4 vs. CHC is warranted.

Women’s Menstrual Cycles and Ovulation Provide Balanced Estradiol and Progesterone for Fertility and Lifelong Health

Prior JC, 2022 · The Cambridge Handbook of Evolutionary Perspectives on Sexual Psychology

Periodic vaginal bleeding occurs in humans (who are henceforth called “women,” a word describing culture as well as biology), old-world apes, and few other mammals. By current concepts, women’s menstrual cycles provide estrogen for thirty to fifty years; following one year of no flow they become menopausal and “estrogen deficient.” By contrast we now know that the purpose of menstrual cycles is to supply all cells and tissues with the balanced essential actions of estradiol (E2) and progesterone (P4) produced in feedback-controlled patterns to facilitate fecundability and preserve younger women’s well-being. We also now know that menopausal women’s health is negatively affected (by increased osteoporosis, heart disease, breast and endometrial cancers) if those past menstrual cycles produced inadequate net P4 to counterbalance and complement E2’s actions. Menstrual periodicity, flow, and ovulatory characteristics in women reflect the integrated actions/interactions of the central nervous system through the hypothalamus and pituitary, ideally leading to each cycle’s stimulation of a dominant egg-containing follicle. That follicle, by central complex feedback loops, produces the cyclic, graded amounts of estradiol (E2) and progesterone (P4) for that threeto five-week period and releases a viable egg. Central reproductive connections allow adult premenopausal women’s menstrual cycle periodicity, ovulation or not, and luteal phase lengths, that can be adapted to the challenges and demands of each woman’s current physiological and sociocultural/emotional environments. These new ideas are based on the differing and complementary cellular and tissue actions of E2 and P4. E2 is essential for cell growth and stimulates cell proliferation. P4 uniquely counterbalances and controls proliferation while stimulating cell differentiation and tissue maturation. Thus, E2–P4 actual and relative productions integrate cycles within each woman’s reproductive lifecycle (adolescent, premenopausal, perimenopausal), and are related to her nutrition, illness, energy expenditure, and social/emotional/spiritual environments. The subtlest indication of a stressed reproductive system is truncated P4 production in the short luteal phase within a normal-length, ovulatory menstrual cycle. This adaptation protects a woman from pregnancy when she has inadequate net energy balance or is under emotional/social/spiritual or physical duress. Thus, a normal luteal phase length within a threeto five-week regular menstrual cycle is a bellwether of women’s well-being. By contrast, regular cycles with ovulatory disturbances (anovulation or short luteal phases; E2>P4) predict current decreased well-being and poor later life health. The purpose of this review is to provide a practical approach to understanding this new women’s menstrual cycle balanced E2–P4 paradigm applied to common clinical situations including subfertility with regular cycles, premenstrual symptoms, and heavy menstrual flow.

Ovarian aging and the perimenopausal transition: the paradox of endogenous ovarian hyperstimulation

Prior JC, 2005 · Endocrine

The purpose of this review is to put into a useful clinical context the changing over time of basic ovarian-pituitary-hypothalamic relationships during perimenopause. "Perimenopause" means changes in ovarian hormones, feedback relationships, and clinical experiences beginning in women ages 35-50 with regular flow and ending 1 yr after the final menstrual flow. A key observation must be explained--estradiol levels are increased in perimenopause. Inhibin B levels are lower and activin may be higher in midlife, menstruating women. These changes probably cause higher follicular phase FSH levels--"endogenous ovarian hyperstimulation" results. The positive estradiol feedback on LH is also disturbed--midcycle LH peaks and mid-luteal slow-frequency, high-amplitude LH pulses are less frequent. In addition to higher levels, estradiol receptors may increase in tissues of symptomatic women. Despite hyperstimulation of follicles, progesterone levels and luteal phase lengths are paradoxically decreased--reasons probably include LH peak disruptions and estrogen-stimulated greater corticotrophin-mediated reproductive suppression. In summary, disturbed feedback relationships causing higher and unpredictable estrogen and lower progesterone levels occur throughout perimenopause, especially during regular cycles. Prospective, population-based research is needed to systematically relate these feedback hormonal changes to clinical characteristics and to allow a diagnosis of perimenopause in regularly cycling midlife women.

Balanced actions of estradiol and progesterone—A new paradigm of women’s reproductive health

Prior JC, 2020 · Drug Discovery Today: Disease Models

Estradiol and progesterone regulate the proliferation of human breast epithelial cells

Foidart JM et al., 1998 · Fertil Steril

To study the effects of estradiol and progesterone on the proliferation of normal human breast epithelial cells in vivo. Double-blind randomized study. Departments of gynecology and of cell biology at a university hospital. PATIENT(S): Forty postmenopausal women with untreated menopause and documented plasma FSH levels of >30 mIU/mL and estradiol levels of <20 pg/mL. INTERVENTION(S): Daily topical application to both breasts of a gel containing a placebo, estradiol, progesterone, or a combination of estradiol and progesterone during the 14 days preceding esthetic breast surgery or excision of a benign lesion. MAIN OUTCOME MEASURE(S): Plasma and breast tissue concentrations of estradiol and progesterone. Epithelial cell cycles were evaluated in normal breast tissue by counting mitoses and performing quantitative proliferating cell nuclear antigen immunolabeling analyses. RESULT(S): Increasing the estradiol concentration enhanced the number of cycling epithelial cells, whereas increasing the progesterone concentration significantly limited the number of cycling epithelial cells. CONCLUSION(S): Exposure to progesterone for 14 days reduced the estradiol-induced proliferation of normal breast epithelial cells in vivo.