The 3D Cohort Study is structured around a triadic (mother‐partner‐child) framework. The cohort comprises 2366 women recruited in the first trimester of pregnancy (8-14 weeks) who were planning to deliver in a collaborating hospital in the province of Quebec. Women and their partners were recruited between May 25, 2010 and August 30, 2012 at one of nine study centres during routine first‐trimester prenatal visits to study hospitals and infertility clinics.