A Video Intervention on Young Adults' Fertility Awareness: a Large-scale Educational RCT in Denmark and Norway Measuring Fecundity Knowledge, Fertility Intentions, Reproductive Behavior and Long-run Impacts on Realized Fertility

This study is an experimental randomized controlled trial (RCT) based on data from the Danish National Birth Cohort (DNBC) and the Norwegian Mother and Child Cohort Study (MoBa). The RCT consists of young adult offspring from these two birth cohorts. The participants in the subsample will randomly be assigned to either an intervention or a control group. The RCT is part of the research project BIOSFER which is funded by an ERC Synergy Grant (European Union, 101071773). The research project aims to investigate the biologic and social causes of low fertility in modern societies.

The Danish National Birth Cohort (DNBC) is an ongoing nationwide cohort of women and their children with more than 20 years of follow-up data (Olsen et al., 2001). The cohort contains 92,000 women recruited 1996 to 2002, who experienced 100,000 pregnancies in total. It has a rich set of background variables including child's development and health up to 18 years, as well as self-reported measures from age 18 onwards. The oldest offspring in the DNBC will be 29 years old at the time of treatment.

The Norwegian Mother, Father and Child Cohort Study (MoBa) is built around 110,000 pregnancies recruited between 1999 and 2008 (Magnus et al., 2016). Children have reported on their own health and exposures from the age of 13, and health and socioeconomic status were reported by the parents before this age. The RCT study will be conducted on a subsample of the MoBa children who are at least 18 years old as of 2024. The oldest offspring in the MoBa will be 25 years old at the time of treatment.

Data collection for the RCT will take place between late 2024 and mid-2025. The RCT intervention group will receive a fecundity knowledge intervention. The intervention consists of a short (3 minutes) animated educational video containing information on risk factors of importance for fecundity.

The primary outcome measure of the RCT is fecundity knowledge. The knowledge level is defined based on the following factors: Age; smoking; sexually transmitted infections; Success of spontaneous pregnancy according to female age; Success of pregnancy according to female age and fertility treatment. The secondary outcomes are: intentions regarding the timing of desired pregnancy/childbirth; fecundity-protective behaviors; life goals; future reproductive behavior- including attempts to conceive, termination of pregnancies and realized fertility The primary and secondary outcomes are measured with validated self-reported questionnaire items - except for certain items under reproductive behavior, such as 'realized fertility', which is measured through registries.