The Environment and Reproductive Health (EARTH) Study is an ongoing
prospective cohort study started in 2006 that recruits couples presenting
to the Massachusetts General Hospital Fertility Center (Boston, MA,
USA). Men are eligible if they are aged 18–55 years, without history of vasectomy,
and are in a couple planning to use their own gametes for fertility
treatment. In April 2007, diet assessment using a food frequency questionnaire
(FFQ) was introduced into the study. For this analysis, we included
men who completed the FFQ and subsequently provided semen samples
up to 18 months after the completion of the FFQ. Of 246 men who met eligibility
criteria, 58 men were excluded due to missing information on dietary
questionnaire, 27 men were excluded because their semen analyses predated
dietary assessment, 5 men were excluded because semen analysis
data were incomplete (4 missing morphology; 1 missing concentration)
and 1 man was excluded due to azoospermia. Of 385 semen samples from