World-wide, there are few existing studies of health outcomes in ART conceived offspring of this age group and sample size, and none of Australian populations [41, 42]. We acknowledge that a retrospective cohort study design is less favourable than a prospective design due to potential recall bias, particularly when assessing areas such as growth and development. However, because we had a large cohort of ART conceived adults a retrospective approach maximised an existing opportunity.
In planning the study, many ethical considerations had to be addressed and most related to privacy. The potential implications for privacy of contacting women up to two decades after their attendance at an ART clinic and not knowing whether they had disclosed the use of ART to their child required sensitive strategies. Initial contact with the ART mothers was through the treating ART service rather than directly from the research team. Also, in case parents had not disclosed the method of conception to their son or daughter, young adults were only contacted with the consent of the mother.
Tracing a current maternal address (exposed group) from details provided so long ago, required multiple strategies, persistence and a substantial amount of time. Eventually 80% of mothers were successfully traced. The use of registered mail, where the addressee has to personally collect the letter at the post office, was essential to ensure receipt of the letter and maintain privacy. However, some stated that they had been alarmed at receiving registered mail as they had believed it may be a police or legal document.
Another challenge in the study design was finding an appropriate comparison group. The decision to use random digit dialing to recruit a spontaneously conceived group was pragmatic but also appropriate given that the aim of the study was to determine the health outcomes of ART conceived offspring rather than the causative effect of ART alone .
Many of the mothers who conceived with ART responded positively to the study invitation expressing their delight in having a child and their desire to assist the research. They were curious about potential health outcomes and interested in the findings. This was also the case with many mothers in the comparison group. A few mothers in the ART group (<1%) responded less favourably as they felt the study to be an invasion of their privacy or it reminded them of a difficult time in their life that they wanted to forget.
The responses to the study invitation from ART conceived young adults were also mostly positive but generally more ‘low key’ than that of their mothers. Although they were interested in the study findings, being ART conceived was often not particularly significant to them personally or something they had given a lot of thought to. Overall, this age group were very busy and finding time to take part was often a challenge. Despite this, when engaged at interview they were usually relaxed and willing to share information, both positive and negative.
The final reminder sent to non-responding mothers in the ART group was very important to the final response rate, increasing it by 11.6%. Many people later stated that they did not respond to the initial letter or the first reminder because they were busy or forgot, were going through a difficult time or lost the original pack. However, the last reminder provided impetus for a substantial number of women to respond. Consequently, we would recommend a ‘final reminder’ some months after the initial invitation to give respondents every opportunity to take part and increase response rate.
Dissemination of the study findings is critical, given the current paucity of knowledge in this area and the increase in demand for ART worldwide. The findings will be published in the peer-reviewed literature and utilised to inform educational materials about the long term health of ART conceived people. Study participants will also be provided with a summary of the key study findings. Finally, publication of the study protocol will assist others planning to follow-up ART populations as they reach adulthood.