PurposePrevious studies have suggested that pregnancy may induce myopia progression. However, no longitudinal study with a large sample size and long-term follow-up has assessed this association. Our objective was to investigate whether pregnancy was related to mid- or long-term myopic refraction changes.Patients and methodsA prospective study was conducted in a Mediterranean cohort. The study included 10 401 women (20-50 years old) from the SUN Project. SUN project is a multipurpose, prospective, and dynamic cohort of university graduates conducted in Spain. The recruitment of participants started in 1999 and it is permanently open. All participants in this cohort had university studies. Participants were followed up for a period of up to 14 years, and pregnancy and refractive changes were assessed through baseline and biennial questionnaires. Pregnancies and myopia were repeatedly assessed in each biennial follow-up questionnaire during a total of 14 years of follow-up.ResultsPregnancy was inversely associated with the risk of myopia development or progression during each of the 2 years periods, with fully adjusted hazard ratio=0.61; (95% confidence interval=0.49-0.75) after adjusting for known potential confounders.ConclusionTo our knowledge this is the first large-longitudinal assessment in young adult women, showing that pregnancy is inversely associated with myopia development or progression. Further studies are needed to confirm these epidemiological findings.