Study design is an internetbased prospective cohort study on lifestyle and fertility in Danish reproductive age women and men. Participants are enrolled during the period where they try to achieve pregnancy – a unique feature of this study compared to other cohort studies on reproductive age women where participants are recruited once they have become pregnant.



Participants are primarily recruited by online methods like banner advertisements on different websites and invitation letters sent through the secure mail system, called e-Boks. They sign up for the study on the SnartForaeldre website and fill in the questionnaires online. Enrollment is based on completion of a comprehensive baseline questionnaire, which takes an average of 22 minutes.


Eligibility criteria

Danish residents can participate in if they are:

  • Aged 18 to 49 years (females) or 18+ years (males)
  • In a stable relationship with a partner of the opposite sex
  • Not using any kind of contraception
  • Trying to achieve pregnancy
  • Not in any kind of fertility treatment



Female participants are asked to complete:

  • A comprehensive baseline questionnaire
  • A food frequency questionnaire
  • A follow-up questionnaire every 8 weeks until they report to be pregnant or for 12 months
  • A short pregnancy questionnaire if they become pregnant

Male participants are asked to complete:

  • A comprehensive baseline questionnaire
  • A food frequency questionnaire



We invite some participants to also participate in a substudy. So far, we have recruited/are planning to recruit participants for substudies on the following topics:

  • Endocrine disrupting chemicals in women (collection of blood and urine samples)
  • Semen quality in men (in-home measurements of semen quality)
  • Sleep in women (registered in a sleep diary app for mobile phones)
  • Physical activity in women (registered by wearing a watch)


Link to registry data

Using the civil registration number, a unique 10-digit number assigned to each Danish resident, data from the self-reported questionnaires can be linked to data from several nationwide registries. This linkage allows for the collection of additional data on potential confounders and outcomes of interest, as well as the independent assessment of the validity of some of the self-reported data, including prescription drug use, reproductive history, and socio-demographic variables.