Wesselink AK, Wise LA, Hatch EE, et al. - Researchers examined the extent to which seasons affect fecundability. In this preconception cohort study, researchers assessed 14,331 women who were residing in North America (June 2013–May 2018: n = 5,827) and Denmark (June 2007–May 2018: n = 8,504) and were attempting to conceive without fertility treatment and had been attempting pregnancy for ≤ 6 menstrual cycles at enrollment. Initiation of pregnancy attempts peaked in September; stronger seasonality was observed in North America vs Denmark (48 vs 16% higher probability initiating attempts in September compared with March). Observations indicated higher fecundability in the fall and lower fecundability in the spring, particularly at lower latitudes after accounting for seasonal patterns in pregnancy planning.