Time to pregnancy recognition among users of an FDA-cleared fertility application.

Background: Previous investigations of time-to-pregnancy recognition have analysed data from national surveys and clinics, but this has not been investigated in the context of digital fertility applications. Timely pregnancy recognition can help individuals in health and pregnancy management, reducing maternal and foetal risk and costs, whilst increasing treatment options, availability, and cost. Methods: This dataset contained 23,728 pregnancies (conceived between June 2018 and December 2022) from 20,429 participants using a Food and Drug Administration (FDA) cleared fertility app in the United States. Most participants (with non-missing information) identified as Non-Hispanic White, and one-third reported obtaining a university degree. We used two-tailed Welch's t-test, Mann-Whitney U-test, and two-tailed Z-tests to compare time to pregnancy recognition between those using the app to conceive or contracept. Results: Participants using an app to conceive recognised pregnancy on average at 31.3 days from last menstrual period (LMP) compared to 35.9 days among those using the app to prevent pregnancy. Conclusion: Generalisability is limited, as all participants were using a fertility app and had relatively homogenous sociodemographic characteristics.

People who recognise pregnancy early may benefit, as earlier recognition can reduce costs and risks, and make more treatment options available. In the past, researchers have studied the time it takes for an individual to recognise that they are pregnant by asking them in national surveys or when they attend a clinic. However, with the advent of digital fertility tracking apps, we investigated the time it takes to recognise pregnancy when using such an app. We analysed data from 23,728 pregnancies from 20,429 users of the Natural Cycles app between June 2018 and December 2022. We found that participants using the app to try to get pregnant recognised pregnancy an average of 4.6 days earlier than those using the app to prevent pregnancy.

Longitudinal changes in sexual desire and attraction among women who started using the Natural Cycles app.

Many women experience sexual side effects, such as decreased libido, when taking hormonal contraceptives (HCs). However, little is known about the extent to which libido recovers after discontinuing HCs, nor about the timeframe in which recovery is expected to occur. Given that HCs suppress the activities of multiple endogenous hormones that regulate both the ovulatory cycle and women's sexual function, resumption of cycles should predict libido recovery. Here, using a combination of repeated and retrospective measures, we examined changes in sexual desire and partner attraction (among partnered women) across a three-month period in a sample of Natural Cycles users (Survey 1: n = 1596; Survey 2: n = 550) who recently discontinued HCs. We also tested whether changes in these outcomes coincided with resumption of the ovulatory cycle and whether they were associated with additional factors related to HC use (e.g., duration of HC use) or relationship characteristics (e.g., relationship length). Results revealed that both sexual desire and partner attraction, on average, increased across three months after beginning to use Natural Cycles. While the prediction that changes in sexual desire would co-occur with cycle resumption was supported, there was also evidence that libido continued to increase even after cycles resumed. Together, these results offer new insights into relationships between HC discontinuation and women's sexual psychology and lay the groundwork for future research exploring the mechanisms underlying these effects.

Timing of Coronavirus Disease 2019 (COVID-19) Vaccination and Effects on Menstrual Cycle Changes.

OBJECTIVE: To assess whether menstrual cycle timing (follicular or luteal phase) of coronavirus disease 2019 (COVID-19) vaccine administration is associated with cycle length changes. METHODS: We used prospectively collected (2021-2022) menstrual cycle tracking data from 19,497 reproductive-aged users of the application "Natural Cycles." We identified whether vaccine was delivered in the follicular or luteal phase and also included an unvaccinated control group. Our primary outcome was the adjusted within-individual change in cycle length (in days) from the average of the three menstrual cycles before the first vaccination cycle (individuals in the unvaccinated control group were assigned a notional vaccine date). We also assessed cycle length changes in the second vaccination cycle and whether a clinically significant change in cycle length (8 days or more) occurred in either cycle. RESULTS: Most individuals were younger than age 35 years (80.1%) and from North America (28.6%), continental Europe (33.5%), or the United Kingdom (31.7%). In the vaccinated group, the majority received an mRNA vaccine (63.8% of the full sample). Individuals vaccinated in the follicular phase experienced an average 1-day longer adjusted cycle length with a first or second dose of COVID-19 vaccine compared with their prevaccination average (first dose: 1.00 day [98.75% CI, 0.88-1.13], second dose: 1.11 days [98.75% CI, 0.93-1.29]); those vaccinated in the luteal phase and those in the unvaccinated control group experienced no change in cycle length (respectively, first dose: -0.09 days [98.75% CI, -0.26 to 0.07], second dose: 0.06 days [98.75% CI, -0.16 to 0.29], unvaccinated notional first dose: 0.08 days [98.75% CI, -0.10 to 0.27], second dose: 0.17 days [98.75% CI, -0.04 to 0.38]). Those vaccinated during the follicular phase were also more likely to experience a clinically significant change in cycle length (8 days or more; first dose: 6.8%) than those vaccinated in the luteal phase or unvaccinated (3.3% and 5.0%, respectively; P <.001). CONCLUSION: COVID-19 vaccine-related cycle length increases are associated with receipt of vaccination in the first half of the menstrual cycle (follicular phase).

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.

A multi-site study of the relationship between photoperiod and ovulation rate using Natural Cycles data.

Many species exhibit seasonal patterns of breeding. Although humans can shield themselves from many season-related stressors, they appear to exhibit seasonal patterns of investment in reproductive function nonetheless, with levels of sex steroid hormones being highest during the spring and summer months. The current research builds on this work, examining the relationship between day length and ovarian function in two large samples of women using data from the Natural Cycles birth control application in each Sweden and the United States. We hypothesized that longer days would predict higher ovulation rates and sexual motivation. Results revealed that increasing day length duration predicts increased ovulation rate and sexual behavior, even while controlling for other relevant factors. Results suggest that day length may contribute to observed variance in women's ovarian function and sexual desire.

Impact of coronavirus disease 2019 (COVID-19) vaccination on menstrual bleeding quantity: An observational cohort study.

OBJECTIVE: To assess whether coronavirus disease 2019 (COVID-19) vaccination impacts menstrual bleeding quantity. DESIGN: Retrospective cohort. SETTING: Five global regions. POPULATION: Vaccinated and unvaccinated individuals with regular menstrual cycles using the digital fertility-awareness application Natural Cycles°. METHODS: We used prospectively collected menstrual cycle data, multivariable longitudinal Poisson generalised estimating equation (GEE) models and multivariable multinomial logistic regression models to calculate the adjusted difference between vaccination groups. All regression models were adjusted for confounding factors. MAIN OUTCOME MEASURES: The mean number of heavy bleeding days (fewer, no change or more) and changes in bleeding quantity (less, no change or more) at three time points (first dose, second dose and post-exposure menses). RESULTS: We included 9555 individuals (7401 vaccinated and 2154 unvaccinated). About two-thirds of individuals reported no change in the number of heavy bleeding days, regardless of vaccination status. After adjusting for confounding factors, there were no significant differences in the number of heavy bleeding days by vaccination status. A larger proportion of vaccinated individuals experienced an increase in total bleeding quantity (34.5% unvaccinated, 38.4% vaccinated; adjusted difference 4.0%, 99.2% CI 0.7%-7.2%). This translates to an estimated 40 additional people per 1000 individuals with normal menstrual cycles who experience a greater total bleeding quantity following the first vaccine dose' suffice. Differences resolved in the cycle post-exposure. CONCLUSIONS: A small increase in the probability of greater total bleeding quantity occurred following the first COVID-19 vaccine dose, which resolved in the cycle after the post-vaccination cycle. The total number of heavy bleeding days did not differ by vaccination status. Our findings can reassure the public that any changes are small and transient.

Association between menstrual cycle length and covid-19 vaccination: global, retrospective cohort study of prospectively collected data.

OBJECTIVES: To identify whether covid-19 vaccines are associated with menstrual changes in order to address concerns about menstrual cycle disruptions after covid-19 vaccination. DESIGN: Global, retrospective cohort study of prospectively collected data. SETTING: International users of the menstrual cycle tracking application, Natural Cycles. PARTICIPANTS: 19 622 individuals aged 18-45 years with cycle lengths of 24-38 days and consecutive data for at least three cycles before and one cycle after covid (vaccinated group; n=14 936), and those with at least four consecutive cycles over a similar time period (unvaccinated group; n=4686). MAIN OUTCOME MEASURES: The mean change within individuals was assessed by vaccination group for cycle and menses length (mean of three cycles before vaccination to the cycles after first and second dose of vaccine and the subsequent cycle). Mixed effects models were used to estimate the adjusted difference in change in cycle and menses length between the vaccinated and unvaccinated. RESULTS: Most people (n=15 713; 80.08%) were younger than 35 years, from the UK (n=6222; 31.71%), US and Canada (28.59%), or Europe (33.55%). Two thirds (9929 (66.48%) of 14 936) of the vaccinated cohort received the Pfizer-BioNTech (BNT162b2) covid-19 vaccine, 17.46% (n=2608) received Moderna (mRNA-1273), 9.06% (n=1353) received Oxford-AstraZeneca (ChAdOx1 nCoV-19), and 1.89% (n=283) received Johnson & Johnson (Ad26.COV2.S). Individuals who were vaccinated had a less than one day adjusted increase in the length of their first and second vaccine cycles, compared with individuals who were not vaccinated (0.71 day increase (99.3% confidence interval 0.47 to 0.96) for first dose; 0.56 day increase (0.28 to 0.84) for second dose). The adjusted difference was larger in people who received two doses in a cycle (3.70 days increase (2.98 to 4.42)). One cycle after vaccination, cycle length was similar to before the vaccine in individuals who received one dose per cycle (0.02 day change (99.3% confidence interval -0.10 to 0.14), but not yet for individuals who received two doses per cycle (0.85 day change (99.3% confidence interval 0.24 to 1.46)) compared with unvaccinated individuals. Changes in cycle length did not differ by the vaccine's mechanism of action (mRNA, adenovirus vector, or inactivated virus). Menses length was unaffected by vaccination. CONCLUSIONS: Covid-19 vaccination is associated with a small and likely to be temporary change in menstrual cycle length but no change in menses length.