The menstrual cycle is influenced by weekly and lunar rhythms.

OBJECTIVE: To study whether the menstrual cycle has a circaseptan (7 days) rhythm and whether it is associated with the lunar cycle (also defined as the synodic month, it is the cycle of the phases of the Moon as seen from Earth, averaging 29.5 days in length). DESIGN: Cross-sectional study. SUBJECTS: A total of 35,940 European and North American women aged 18-40 years. EXPOSURE: Data were collected in real-life conditions. INTERVENTION: No intervention was performed. MAIN OUTCOME MEASURE: The onset of menstruation was assessed in prospectively measured menstrual cycles (311,064 cycles) over 3 full years (2019-2021). Associations were calculated between the onset of menstruation and the day of the week, and between the onset of menstruation and the lunar phase. RESULTS: In this large data set, a circaseptan (7-day) rhythmicity of menstruation was observed, with a peak (acrophase) of menstrual onset on Thursdays and Fridays. This circaseptan rhythm was observed in every age group, in every phase of the lunar cycle, and in all seasons. This feature was most pronounced for cycle durations between 27 and 29 days. In winter, the circaseptan rhythm was found in cycles of 27-29 days, but not in other cycle lengths. A circalunar rhythm was also statistically significant, but not as clearly defined as the circaseptan rhythm. The peak (acrophase) of the circalunar rhythm of menstrual onset varied according to the season. In addition, there was a small but statistically significant interaction between the circaseptan rhythm and the lunar cycle. CONCLUSION: Although relatively small in amplitude, the weekly rhythm of menstruation was statistically significant. Menstruation occurs more often on Thursdays and Fridays than on other days of the week. This is particularly true for women whose cycles last between 27 and 29 days. Circalunar rhythmicity was also statistically significant. However, it is less pronounced than the weekly rhythm.

Using Quantitative Hormone Monitoring to Identify the Postpartum Return of Fertility.

Background and Objectives: The Marquette Method (MM) has been used for many years to track the postpartum return of fertility using the ClearBlue Fertility Monitor (CBFM). A new quantitative urine hormone monitor (the Mira Analyzer) was compared to the CBFM in one previous study, and using this pilot data, several women have started to use the Mira Analyzer in the postpartum transition to fertility. Materials and Methods: This study was a retrospective, observational case series that analyzed hormone data on the Mira Analyzer during the postpartum period. Participants were invited to share their postpartum cycle and hormone observations. Quantitative hormones in the urine included estrone-3-glucuronide (E3G), luteinizing hormone (LH), and pregnanediol glucuronide (PDG). Data were collected using an electronic survey and an online portal for hormone data. Data collected included participant demographics, menstrual cycle characteristics, and reproductive health history. Hormone range values were calculated, and thresholds were identified that would best predict the first ovulation that led to the first postpartum menstrual period, as well as in transition cycles. Hormone patterns were identified in the context of previous studies. Results: Twenty participants contributed data for the analysis. Triggering ovulation before the first period postpartum (Cycle 0) usually required higher LH thresholds than for regularly cycling women. Three different patterns were observed in the return of fertility postpartum: minimal ovarian activity, follicular activity without ovulation, and the early return of fertility. Abstinence rates for avoiding pregnancy with experimental thresholds were calculated. Conclusions: Higher LH thresholds in Cycle 0 suggest a decreased responsiveness of the ovaries to LH stimulation from the pituitary. This study replicates postpartum hormone patterns from a previous study. Larger studies are planned to evaluate the effectiveness for avoiding pregnancy using the Mira Analyzer in the postpartum return of fertility.

Survey Analysis of Quantitative and Qualitative Menstrual Cycle Tracking Technologies.

Background and Objectives: Digital health and personalized medicine are advancing at an unprecedented pace. Users can document their menstrual cycle data in a variety of ways, including smartphone applications (apps), temperature tracking devices, and at-home urine hormone tests. Understanding the needs and goals of women using menstrual cycle tracking technologies is the first step to making these technologies more evidence based. The purpose of this study was to examine the current use of these technologies and explore how they are being used within the context of common hormonal and reproductive disorders, like polycystic ovary syndrome (PCOS), endometriosis, and infertility. Materials and Methods: This was a cross-sectional study evaluating menstrual cycle tracking technology use. Participants were recruited in January-March 2023 using social media groups and a Marquette Method instructor email listserv. Data were collected using an electronic survey with Qualtrics. Data collected included participant demographics, menstrual cycle characteristics, reproductive health history, and menstrual cycle tracking behavior. Results: Three-hundred and sixty-eight participants were included in the analysis. Women had various motivations for tracking their menstrual cycles. Most participants (72.8%) selected "to avoid getting pregnant" as the primary motivation. Three hundred and fifty-six participants (96.7%) reported using a fertility awareness-based method to track and interpret their menstrual cycle data. The Marquette Method, which utilizes urine hormone tracking, was the most frequently used method (n = 274, 68.2%). The most frequently used cycle technology was a urine hormone test or monitor (n = 299, 81.3%), followed by a smartphone app (n = 253, 68.8%), and a temperature tracking device (n = 116, 31.5%). Women with PCOS (63.6%), endometriosis (61.8%), and infertility (75%) in our study reported that the use of tracking technologies aided in the diagnosis. Most participants (87.2%) reported a high degree of satisfaction with their use and that they contributed to their reproductive health knowledge (73.9%). Conclusions: Women in our study reported avoiding pregnancy as their primary motivation for using menstrual cycle tracking technologies, with the most frequently used being a urine hormone test or monitor. Our study results emphasize the need to validate these technologies to support their use for family planning. Given that most women in this study reported using a fertility awareness-based method, the results cannot be generalized to all users of menstrual cycle tracking technologies.

Establishing a Gold Standard for Quantitative Menstrual Cycle Monitoring.

Background and Objectives: The Quantum Menstrual Health Monitoring Study will measure four key reproductive hormones in the urine (follicle-stimulating hormone, FSH; estrone-3-glucuronide, E13G; luteinizing hormone, LH; and pregnanediol glucuronide, PDG) to characterize patterns that predict and confirm ovulation, referenced to serum hormones and the gold standard of the ultrasound day of ovulation in participants with regular cycles. These normal cycles will provide a reference for comparison to irregular cycles in subjects with polycystic ovarian syndrome (PCOS) and athletes. Materials and Methods: Participants will track their menstrual cycles for 3 months and be provided with an at-home urine hormone monitor (Mira monitor) to predict ovulation. The day of ovulation will be confirmed with serial ultrasounds completed in a community clinic. Urine results will be compared to serum hormone values. Other markers of menstrual health, such as bleeding patterns and temperature changes, will be determined using a customized app. Three groups will be recruited. Group 1 will include those with consistent regular cycle lengths (between 24-38 days), and will be compared to two groups with irregular cycle lengths (with increased cycle length variability and longer cycles). Group 2 will include those with polycystic ovarian syndrome (PCOS) with irregular cycles and Group 3 will include individuals participating in high levels of exercise with irregular cycles. Hypothesis: The Mira monitor quantitative urine hormone pattern will accurately correlate with serum hormonal levels and will predict (with LH) and confirm (with PDG) the ultrasound day of ovulation in those with regular cycles as well as those with irregular cycles. Rationale: Once the ultrasound validation is complete, tools like the Mira monitor with a customized app may become a new standard for at-home and remote clinical monitoring of the menstrual cycle without having to use labor-intensive follicular-tracking ultrasound or follow serum hormone changes. Conclusions: Precision monitoring of the menstrual cycle is expected to impact individuals who want to increase their menstrual health literacy and guide decisions about fertility.

Effectiveness of a Postpartum Breastfeeding Protocol for Avoiding Pregnancy.

The uses of cervical mucus and basal body temperature as indicators of return to fertility postpartum have resulted in high unintended pregnancy rates. In 2013, a study found that when women used urine hormone signs in a postpartum/breastfeeding protocol this resulted in fewer pregnancies. To improve the original protocol's effectiveness, three revisions were made: (1) women were to increase the number of days tested with the Clearblue Fertility Monitor, (2) an optional second luteinizing hormone test could be done in the evening, and (3) instructions were given to manage the beginning of the fertile window for the first six cycles postpartum. The purpose of this study was to determine the correct and typical use effectiveness rates to avoid pregnancy in women who used a revised postpartum/breastfeeding protocol. A cohort review of an established data set from 207 postpartum breastfeeding women who used the protocol to avoid pregnancy was completed using Kaplan-Meier survival analysis. Total pregnancy rates that included correct and incorrect use pregnancies were eighteen per one hundred women over twelve cycles of use. For the pregnancies that met a priori criteria, the correct use pregnancy rates were two per one hundred over twelve months and twelve cycles of use and typical use rates were four per one hundred women at twelve cycles of use. The protocol had fewer unplanned pregnancies than the original, however, the cost of the method increased.

The Garden of Forking Paths; An Evaluation of Joseph's 'A Reevaluation of the 1990 "Minnesota Study of Twins Reared Apart" IQ Study'.

Joseph has written what purports to be a refutation of studies of Twins Reared-Apart (TRAs) with a singular focus on the Minnesota Study of Twins Reared-Apart (MISTRA). I show, in detail, that (a) his criticisms of previous TRA studies depend on sources that were discredited prior to MISTRA, as they all failed the test of replicability, (b) the list of biases he uses to invalidate MISTRA do not support his arguments, (c) the accusations of questionable research practices are unsubstantiated, (d) his claim that MISTRA should be evaluated in the context of psychology's replication crisis is refuted. The TRA studies are constructive replications. Like many other scholars, past and present, he has been misled by the variation introduced by small samples (sampling error) and the distortion created by walking in the garden of forking paths. His endeavor is a concatenation of elision and erroneous statistical/scientific reasoning.

Using Quantitative Hormonal Fertility Monitors to Evaluate the Luteal Phase: Proof of Concept Case Study.

Several new quantitative fertility monitors are now available for at-home use that measure estrogen, luteinizing hormone (LH), and progesterone (PDG) in urine. This case report compares the Mira and Inito quantitative fertility monitors with the well-established qualitative ClearBlue fertility monitor. Three clinical scenarios were evaluated: a normal cycle, a prolonged luteinization cycle, and an anovulatory cycle. The identification of the luteal phase (or lack thereof in the case of anovulation) and the transition through the three processes of luteinization, progestation, and luteolysis were clearly demarcated with the help of quantitative LH and PDG. Quantitative fertility monitors have the potential to identify details of the luteal phase to help women with regular cycles and abnormal luteal phases to help target interventions for optimizing fertility.

Distinct urinary progesterone metabolite profiles during the luteal phase.

OBJECTIVES: During normal menstrual cycles, serum levels of progesterone vary widely between cycles of same woman and between women. This study investigated the profiles of pregnanediol during the luteal phase. METHODS: Data stemmed from a previous multicenter prospective observational study and concerned 107 women (who contributed 326 menstrual cycles). The study analyzed changes in observed cervical mucus discharge, various hormones in first morning urine, and serum progesterone. Transvaginal ultrasonography and cervical mucus helped identifying the day of ovulation. Changes in pregnanediol glucuronide levels during the luteal phase were examined and classified according to the length of that phase, a location parameter, and a scale parameter. Associations between nine pregnanediol glucuronide profiles and other hormone profiles were examined. RESULTS: Low periovulatory pregnanediol glucuronide levels and low periovulatory luteinizing hormone levels were associated with delayed increases in pregnanediol glucuronide after ovulation. That 'delayed increase profile' was more frequently associated with cycles with prolonged high LH levels than in cycles with rapid pregnanediol glucuronide increases. A 'plateau-like profile' during the luteal phase was associated with longer cycles, cycles with higher estrone-3-glucuronide and pregnanediol glucuronide during the preovulatory phase, and cycles with higher periovulatory pregnanediol glucuronide levels. CONCLUSIONS: Distinct profiles of urinary progesterone levels are displayed during the luteal phase. These profiles relate to early hormone changes during the menstrual cycle. In everyday clinical practice, these findings provide further evidence for recommending progesterone test seven days after the mucus peak day. The search for other correlations and associations is underway.

Menstrual Cycle Parameters Are Not Significantly Different After COVID-19 Vaccination.

Background: Some studies have suggested minor changes in the menstrual cycle after COVID-19 vaccination, but more detailed analyses of the menstrual cycle are needed to evaluate more specific changes in the menstrual cycle that are not affected by survey-based recall bias. Materials and Methods: Using a pretest-post-test quasi-experimental evaluation of menstrual cycle parameters before and after COVID-19 vaccination, we conducted an anonymous online survey of two groups of North American women who prospectively monitor their menstrual cycle parameters daily including bleeding patterns, urinary hormone levels using the ClearBlue Fertility Monitor, or cervical mucus observations. The primary outcome measures were cycle length, length of menses, menstrual volume, estimated day of ovulation (EDO), luteal phase length, and signs of ovulation. Perceived (subjective) menstrual cycle changes and stressors were also evaluated in this study as secondary outcome measures. Results: Of the 279 women who initiated the survey, 76 met the inclusion criteria and provided 588 cycles for analysis (227 pre-vaccine cycles, 145 vaccine cycles, 216 post-vaccine cycles). Although 22% of women subjectively identified changes in their menstrual cycle, there were no significant differences in menstrual cycle parameters (cycle length, length of menses, EOD, and luteal phase length) between the pre-vaccine, vaccine, and post-vaccine cycles. Conclusions: COVID-19 vaccines were not associated with significant changes in menstrual cycle parameters. Perceived changes by an individual woman must be compared with statistical changes to avoid confirmation bias.

Multisite Effectiveness Study of the Marquette Method of Natural Family Planning Program.

Women of reproductive age need reliable and effective family planning methods to manage their fertility. Natural family planning (NFP) methods or fertility awareness-based methods (FABMs) have been increasingly used by women due to their health benefits. Nevertheless, effectiveness of these natural methods remains inconsistent, and these methods are difficult for healthcare providers to implement in their clinical practice. The purpose of this study is to evaluate the effectiveness of the Marquette Model NFP system to avoid pregnancy for women at multiple teaching sites using twelve months of retrospectively collected teaching data. Survival analysis (Kaplan-Meier) was used to determine typical unintended pregnancy rates for a total of 1,221 women. There were forty-two unintended pregnancies which provided a typical use unintended pregnancy rate of 6.7 per 100 women over twelve months of use. Eleven of the forty-two unintended pregnancies were associated with correct use of the method. The total unintended pregnancy rate over twelve months of use was 2.8 per 100 for women with regular cycles, 8.0 per 100 women for the postpartum and breastfeeding women, and 4.3 per 100 for women with irregular menstrual cycles. The Marquette Model system of NFP was effective when provided by health professionals who completed the Marquette Model NFP teacher training program. Summary: This study involved determining whether healthcare professionals at ten sites across the United States and Canada trained to provide the Marquette Method NFP services can replicate the effectiveness demonstrated in previous studies of the method. We found a high level of effectiveness (i.e., very low pregnancy rates) in using the Marquette Method among women from various regions across North America with diverse reproductive backgrounds and in particular when using hormonal fertility marker. Healthcare providers who have been trained to teach NFP can successfully incorporate NFP services in their practice and assist their clients in choosing appropriate family planning methods.

Descriptive analysis of the relationship between progesterone and basal body temperature across the menstrual cycle.

OBJECTIVE: Describe the relationship between basal body temperature (BBT) and pregnanediol-3 alpha-glucuronide (PDG, the urine metabolite of progesterone) across the menstrual cycle. DESIGN: Observational study. SETTING: Study carried out from 1996 to 1997 in eight European family planning clinics. PARTICIPANT(S): One hundred and seven normally fertile and cycling women. MAIN OUTCOME MEASURE(S): BBT and PDG level on each day of 283 cycles and ultrasound determination of the day of ovulation. RESULT: (s): In comparison with previous end-of-cycle levels, decreases in PDG and BBT on the first day of menses were seen in nearly 90% and 80% of cycles, respectively. In a non-negligible percentage of cycles, luteolysis would continue during menses: between the second and the third day after menses, small but significant decreases in PDG and BBT were seen in 76% and 48% of cycles, respectively. During the peri-ovulatory phase, between the third and the second day before ovulation, PDG and BBT began to rise in 56% and 41% of cycles, respectively. There was a medium degree of correlation between PDG levels and BBT (r = 0.53; 7,279 days with available measurements). The relationship between PDG levels and BBT was linear at low PDG levels but BBT increased no longer when PDG levels continued to rise above a threshold of nearly 10 mcg/mg Cr. CONCLUSION: (s): PDG and BBT had parallel increases at low PDG rates but diverged at higher rates.

Quantitative versus qualitative estrogen and luteinizing hormone testing for personal fertility monitoring.

BACKGROUND: A new fertility monitor is now available that provides quantitative measurement of urinary hormones, but clinical use requires validation against an established fertility monitor that provides only qualitative results. RESEARCH DESIGN AND METHODS: Two fertility monitors were compared using daily first morning urine samples over 3 cycles of use in 21 women users with experience using a fertility monitor with the Marquette Method of Natural Family Planning. RESULTS: Women were aged 33.4 ± 5.5 years and had menstrual cycles ranging between 23 and 41 days. The quantitative Mira Monitor estimates of ovulation were highly correlated with the qualitative ClearBlue Fertility Monitor (CBFM) estimates of ovulation. Both monitors provided an accurate estimate of the fertile window. CONCLUSIONS: In this preliminary trial, the Mira monitor was shown to be effective at delineating the fertile window and ovulation. We demonstrated the feasibility of applying the Marquette Method algorithm with the use of the Mira monitor. Satisfaction differences between the two monitors did not reach statistical significance. We anticipate that quantitative fertility monitoring will give couples and health-care providers new and unprecedented insights into the menstrual cycle and fertility.

Pilot Evaluation of a New Urine Progesterone Test to Confirm Ovulation in Women Using a Fertility Monitor.

Background: Progesterone rises ~24-36 h after ovulation. Past studies using ultrasound-confirmed ovulation have shown that three consecutive tests with a threshold of 5µg/mL of urine progesterone (pregnanediol-3-glucuronide, PDG), taken after the luteinizing hormone (LH) surge, confirmed ovulation with 100% specificity. Purpose: The purpose of this study was to a evaluate a new urine PDG self-test to retrospectively confirm ovulation in women who were monitoring ovulation using a hormonal fertility monitor. Methods: Thirteen women of reproductive age were recruited to test urine PDG while using their home hormonal fertility monitor. The monitor measured the rise in estrogen (estrone-3-glucuronide, E3G) and LH to estimate the fertile phase of the menstrual cycle. The women used an online menstrual cycle charting system to track E3G, LH and PDG levels for four menstrual cycles. Results: The participants (Mean age 33.6) produced 34 menstrual cycles of data (Mean length 28.4 days), 17 of which used a PDG test with a threshold of 7µg/mL and 17 with a threshold of 5µg/mL. In the cycles that used the 7µg/mL test strips, 59% had a positive confirmation of ovulation, and with the 5µg/mL test strips, 82% of them had a positive confirmation of ovulation. Conclusion: The 5µg/mL PDG test confirmed ovulation in 82% of cycles and could assist women in the evaluation of the luteal progesterone rise of their menstrual cycle.

Pilot observational prospective cohort study on the use of a novel home-based urinary pregnanediol 3-glucuronide (PDG) test to confirm ovulation when used as adjunct to fertility awareness methods (FAMs) stage 1.

RATIONALE: Ovulation confirmation is a fundamental component of the evaluation of infertility. PURPOSE: To inform the design of a larger clinical trial to determine the effectiveness of a new home-based pregnanediol glucuronide (PDG) urine test to confirm ovulation when compared with the standard of serum progesterone. METHODS: In this observational prospective cohort study (single group assignment) in an urban setting (stage 1), a convenience sample of 25 women (aged 18-42 years) collected daily first morning urine for luteinisinghormone (LH), PDG and kept a daily record of their cervical mucus for one menstrual cycle. Serum progesterone levels were measured to confirm ovulation. Sensitivity and specificity were used as the main outcome measures. Estimation of number of ultrasound (US)-monitored cycles needed for a future study was done using an exact binomial CI approach. RESULTS: Recruitment over 3 months was achieved (n=28) primarily via natural fertility regulation social groups. With an attrition rate of 22%, specificity of the test was 100% for confirming ovulation. Sensitivity varied depending on whether a peak-fertility mucus day or a positive LH test was observed during the cycle (85%-88%). Fifty per cent of participants found the test results easy to determine. A total of 73 US-monitored cycles would be needed to offer a narrow CI between 95% and 100%. CONCLUSION: This is first study to clinically evaluate this test when used as adjunct to the fertility awareness methods. While this pilot study was not powered to validate or test efficacy, it helped to provide information on power, recruitment and retention, acceptability of the procedures and ease of its use by the participants. Given this test had a preliminary result of 100% specificity, further research with a larger clinical trial (stage 2) is recommended to both improve this technology and incorporate additional approaches to confirm ovulation. TRIAL REGISTRATION NUMBER: NCT03230084.

Corrigendum: Urinary Luteinizing Hormone Tests: Which Concentration Threshold Best Predicts Ovulation?

[This corrects the article DOI: 10.3389/fpubh.2017.00320.].

Have Standard Formulas Correcting Correlations for Range Restriction Been Adequately Tested?: Minor Sampling Distribution Quirks Distort Them.

Most study samples show less variability in key variables than do their source populations due most often to indirect selection into study participation associated with a wide range of personal and circumstantial characteristics. Formulas exist to correct the distortions of population-level correlations created. Formula accuracy has been tested using simulated normally distributed data, but empirical data are rarely available for testing. We did so in a rare data set in which it was possible: the 6-Day Sample, a representative subsample of 1,208 from the Scottish Mental Survey 1947 of cognitive ability in 1936-born Scottish schoolchildren (70,805). 6-Day Sample participants completed a follow-up assessment in childhood and were re-recruited for study at age 77 years. We compared full 6-Day Sample correlations of early-life variables with those of the range-restricted correlations in the later-participating subsample, before and after adjustment for direct and indirect range restriction. Results differed, especially for two highly correlated cognitive tests; neither reproduced full-sample correlations well due to small deviations from normal distribution in skew and kurtosis. Maximum likelihood estimates did little better. To assess these results' typicality, we simulated sample selection and made similar comparisons using the 42 cognitive ability tests administered to the Minnesota Study of Twins Reared Apart, with very similar results. We discuss problems in developing further adjustments to offset range-restriction distortions and possible approaches to solutions.

Influence of Contraception Use on the Reproductive Health of Adolescents and Young Adults.

Oral contraceptives (OCs) are often prescribed to adolescents and young adults for the treatment of health problems and to avoid unwanted pregnancies. We hypothesized that the use of OCs, among adolescents and young adults, is associated with a greater likelihood of pregnancy, abortion, sexually transmitted diseases (STDs), pelvic inflammatory disease (PID), and sexual behaviors that will enhance those problems (i.e., earlier sexual debut and more sexual partners) than adolescents and young adults not using OCs. To test this hypothesis, data from 1,365 adolescents and young adults in the 2011-2013 National Survey of Family Growth (NSFG) were used to describe the influence of ever use of OCs on ever having sex, sexual debut, multiple sexual partners, STDs, PID, pregnancy, and abortion. A secondary purpose was to evaluate protective factors from unhealthy sexual practices like religiosity, church attendance, and intact families. We found that the "ever use" of OCs by US adolescents and young adults results in a greater likelihood of ever having sex, STDs, PID, pregnancy, and abortion compared with those adolescents and young adults who never used OCs. Furthermore, those adolescents who ever used OCs had significantly more male sexual partners than those who never used OCs, and they also had an earlier sexual debut by almost two years. Conversely, we found that frequent church attendance, identification of the importance of religion, and having an intact family among adolescents were associated with less likelihood of unsafe sexual practices. We concluded that the use of OCs by adolescents and young adults might be considered a health risk. Further research is recommended to confirm these associations. Summary: The purpose of this article was to show the correlation between contraceptive use in adolescents and negative sexual outcomes. We used data from the 2011-2013 NSFG and demonstrated that never married adolescents who used oral hormonal contraception were three times more likely to have an STD, have PID, and to become pregnant, and, surprisingly, ten times more likely of having an abortion compared to noncontracepting adolescents. These are outcomes that contraception is intended to prevent. These data also showed that the contraceptors had significantly more male partners than their contraceptive counterparts. Protective factors such as church attendance and family cohesiveness were associated with a decreased likelihood of sexual activity.

Hormonal Predictors of Abnormal Luteal Phases in Normally Cycling Women.

Objective: Explore potential relationships between preovulatory, periovulatory, and luteal-phase characteristics in normally cycling women. Design: Observational study. Setting: Eight European natural family planning clinics. Patient(s): Ninety-nine women contributing 266 menstrual cycles. Intervention(s): The participants collected first morning urine samples that were analyzed for estrone-3 glucuronide (E1G), pregnanediol-3- alpha-glucuronide (PDG), follicle stimulating hormone (FSH), and luteinizing hormone (LH). The participants underwent serial ovarian ultrasound examinations. Main Outcome Measure(s): Four outcome measures were analyzed: short luteal phase, low mid-luteal phase PDG level (mPDG), normal then low luteal PDG level, low then normal luteal PDG level. Results: A long preovulatory phase was a predictor of short luteal phase, with or without adjustment for other variables. A high periovulatory PDG level was a predictor for short luteal phase as well as normal then low luteal PDG level. A low periovulatory PDG level predicted low mPDG and low then normal luteal PDG level, with or without adjustment for other variables. A small maximum follicle predicted normal then low luteal PDG level, with or without adjustment for other variables. The relationship between small maximum follicle size and short luteal phase or small maximum follicle size and low mPDG was no longer present when the regression was adjusted for certain characteristics. A younger age at menarche and a high body mass index were both predictors of low mPDG. Conclusion: Luteal phase abnormalities exist over a spectrum where some ovulation disorders may exist as deviations from the normal ovulatory process.This study confirms the negative impact of a small follicle size on the quality of the luteal phase. The occurrence of normal then low luteal PDG level is confirmed as a potential sign of luteal phase abnormality.