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We prospectively examined the association between COVID-19 vaccination and menstrual cycle characteristics in an internet-based prospective cohort study. We included a sample of 1,137 participants who enrolled in Pregnancy Study Online (PRESTO), a preconception cohort study of couples trying to conceive, during January 2021-August 2022. Eligible participants were aged 21–45 years, United States or Canadian residents, and trying to conceive without fertility treatment. At baseline and every 8 weeks for up to 12 months, participants completed questionnaires on which they provided information on COVID-19 vaccination and menstrual cycle characteristics, including cycle regularity, cycle length, bleed length, heaviness of bleed, and menstrual pain. We fit generalized estimating equation (GEE) models with a log link function and Poisson distribution to estimate the adjusted risk ratio (RR) for irregular cycles associated with COVID-19 vaccination. We used linear regression with GEE to estimate adjusted mean differences in menstrual cycle length associated with COVID-19 vaccination. We adjusted for sociodemographic, lifestyle, medical and reproductive factors. Participants had 1.1 day longer menstrual cycles after receiving the first dose of COVID-19 vaccine (95 % CI: 0.4, 1.9) and 1.3 day longer cycles after receiving the second dose (95 % CI: 0.2, 2.5). Associations were attenuated at the second cycle post-vaccination. We did not observe strong associations between COVID-19 vaccination and cycle regularity, bleed length, heaviness of bleed, or menstrual pain. In conclusion, COVID-19 vaccination was associated with a ∼1 day temporary increase in menstrual cycle length, but was not appreciably associated with other menstrual cycle characteristics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Residential ambient concentrations of particulate matter, nitrogen dioxide, and ozone were not strongly associated with fecundability, the per cycle probability of conception. • We examined concentrations during multiple critical windows of exposure. • This is one of the largest studies to examine this association among couples trying to conceive spontaneously. Animal and epidemiologic studies indicate that air pollution may adversely affect fertility. However, the level of evidence is limited and specific pollutants driving the association are inconsistent across studies. We used data from a web-based preconception cohort study of pregnancy planners enrolled during 2013–2019 (Pregnancy Study Online; PRESTO). Eligible participants self-identified as female, were aged 21–45 years, resided in the United States (U.S.) or Canada, and were trying to conceive without fertility treatments. Participants completed a baseline questionnaire and bi-monthly follow-up questionnaires until conception or 12 months. We analyzed data from 8,747 participants (U.S.: 7,304; Canada: 1,443) who had been trying to conceive for < 12 cycles at enrollment. We estimated residential ambient concentrations of particulate matter < 2.5 µm (PM 2.5), nitrogen dioxide (NO 2), and ozone (O 3) using validated spatiotemporal models specific to each country. We fit country-specific proportional probabilities regression models to estimate the association between annual average, menstrual cycle-specific, and preconception average pollutant concentrations with fecundability, the per-cycle probability of conception. We calculated fecundability ratios (FRs) and 95% confidence intervals (CIs) and adjusted for individual- and neighborhood-level confounders. In the U.S., the FRs for a 5-µg/m3 increase in annual average, cycle-specific, and preconception average PM 2.5 concentrations were 0.94 (95% CI: 0.83, 1.08), 1.00 (95% CI: 0.93, 1.07), and 1.00 (95% CI: 0.93, 1.09), respectively. In Canada, the corresponding FRs were 0.92 (95% CI: 0.74, 1.16), 0.97 (95% CI: 0.87, 1.09), and 0.94 (95% CI: 0.80, 1.09), respectively. Likewise, NO 2 and O 3 concentrations were not strongly associated with fecundability in either country. Neither annual average, menstrual cycle-specific, nor preconception average exposure to ambient PM 2.5 , NO 2 , and O 3 were appreciably associated with reduced fecundability in this cohort of pregnancy planners. [ABSTRACT FROM AUTHOR]

Study Question: To what extent does fecundability vary across seasons?Summary Answer: After accounting for seasonal patterns in pregnancy planning, we observed higher fecundability in the fall and lower fecundability in the spring, particularly at lower latitudes.What Is Known Already: In human populations, there are strong seasonal patterns of births that vary across geographic regions and time periods. However, previous studies of seasonality and fecundity are limited because they examine season of birth rather than season of conception and therefore neglect to account for seasonal variation in initiating attempts to conceive or pregnancy loss or differences in gestational length.Study Design, Size, Duration: We conducted a preconception cohort study of 14 331 women residing in North America (June 2013-May 2018: n = 5827) and Denmark (June 2007-May 2018: n = 8504). Participants were attempting to conceive without fertility treatment and had been attempting pregnancy for ≤6 menstrual cycles at enrolment.Participants/material, Setting, Methods: We collected information on season of each pregnancy attempt using last menstrual period dates over the study period. Pregnancy was reported on female bi-monthly follow-up questionnaires. We fit log-binomial models with trigonometric regression to examine periodic variation in fecundability. We accounted for seasonal variation in initiation of pregnancy attempts by including indicator variables for menstrual cycle of attempt in the regression models.Main Results and the Role Of Chance: Initiation of pregnancy attempts peaked in September, with stronger seasonality in North America than in Denmark (48 vs. 16% higher probability initiating attempts in September compared with March). After accounting for seasonal variation in initiation of pregnancy attempts, we observed modest seasonal variation in fecundability, with a peak in the late fall and early winter in both cohorts, but stronger peak/low ratios in North America (1.16; 95% confidence interval [CI]: 1.05, 1.28) than in Denmark (1.08; 95% CI: 1.00, 1.16). When we stratified the North American data by latitude, we observed the strongest seasonal variation in the southern USA (peak/low ratio of 1.45 [95% CI: 1.14, 1.84]), with peak fecundability in late November.Limitations, Reasons For Caution: We estimated menstrual cycle dates between follow-up questionnaires, which may have introduced exposure misclassification, particularly when women skipped follow-up questionnaires. We were unable to measure seasonally varying factors that may have influenced fecundability, including ambient temperature, vitamin D levels or infectious disease.Wider Implications Of the Findings: An understanding of how fecundability varies across seasons could help identify factors that can impair reproductive function. Neglecting to account for seasonal variation in initiation of pregnancy attempts could bias estimates of seasonal patterns in fecundability. This is the first preconception cohort study to examine seasonal variation in fecundability after accounting for seasonality in initiation of pregnancy attempts. Fecundability was highest in the fall and lowest in the spring, with stronger effects in southern latitudes of North America, suggesting that seasonal exposures may affect fecundity.Study Funding/competing Interest(s): This research was funded by the Eunice K. Shriver National Institute of Child Health and Human Development (R21-050264, R01-HD060680, R21-HD072326 and R01-HD086742) and the Danish Medical Research Council (271-07-0338). The authors declare no conflicts of interest. [ABSTRACT FROM AUTHOR]

Purpose: To prospectively examine the association between time-to-pregnancy (TTP) and postpartum depression (PPD) and determine whether perceived stress during early pregnancy mediated this association.Methods: In Pregnancy Study Online, an internet-based preconception cohort study of pregnancy planners, participants completed questionnaires every 8 weeks for up to 12 months or conception, during pregnancy, and at postpartum. A total of 2643 women provided information on sociodemographic factors, reproductive history, and stress (i.e., Perceived Stress Scale [PSS]) during preconception and early pregnancy (completed at ∼4-12 weeks' gestation) and on postpartum depressive symptoms (i.e., Edinburgh Postnatal Depression Scale [EPDS]) at ∼6 months postpartum. We used multivariable modified Poisson regression models to estimate risk ratios and 95% confidence intervals (CIs) for the association between TTP (<3, 3-5, 6-11, ≥12 menstrual cycles) and PPD (EPDS score ≥13). Causal mediation analyses assessed the mediating role of early pregnancy PSS scores.Results: 10.6% of women had EPDS scores indicating possible PPD (≥13). Compared with women who took less than 3 cycles to conceive, risk ratios for those who took 3-5, 6-11, and greater than or equal to 12 were 1.06 (95% CI: 0.77, 1.45), 1.24 (95% CI: 0.90, 1.70), and 1.31 (95% CI: 0.87, 1.99), respectively. Approximately 30% of the association between infertility (TTP ≥ 12) and PPD was mediated by early pregnancy PSS.Conclusions: There was a modest positive dose-response association between delayed conception and PPD. Perceived stress in early pregnancy explained a small proportion of this association. However, given the width of the CIs, chance cannot be ruled out as an explanation for the observed association. [ABSTRACT FROM AUTHOR]