Study question: What is the predictive ability of the Desire to Avoid Pregnancy Scale, with regard to pregnancy within one year, and how could it be used as a screening tool? Summary answer: The Desire to Avoid Pregnancy (DAP) Scale is highly predictive of pregnancy within one year and could be used as a screening tool with a suitable cut-point selected according to the purpose. What is known already: There is no existing screening instrument that can reliably predict pregnancy. The Desire to Avoid Pregnancy Scale is a new measure; understanding its sensitivity and specificity as a screening tool for pregnancy as well as its predictive ability and how this varies by socio-demographic factors is important to inform its implementation. Study design, size, duration: A prospective cohort study of 994 non-pregnant women in the UK, with desire to avoid pregnancy measured at baseline and occurrence of pregnancy assessed every quarter for one year. Almost 95% of eligible participants completed follow-up at 12 months; those lost to follow-up were not significantly different on key socio-demographic factors. Participants/materials, setting, methods: The cohort was recruited using social media as well as advertisements in a university, school, abortion clinic and outreach sexual health service. Participants completed an online survey at baseline in October 2018 and every quarter for a year. We used baseline DAP score and a binary variable of whether they had experienced pregnancy during the study to assess the sensitivity, specificity, area under the ROC curve (AUROC) and positive and negative predictive values (PPV and NPV) of the DAP at a range of cut-points. We also examined how the predictive ability of the DAP varied according to socio-demographic factors and by the time frame considered (e.g., pregnancy within 3, 6, 9 and 12 months). Main results and the role of chance: At a cut-point of <2 on the 0-4 range of the DAP scale, scale score had a sensitivity of 0.78 and specificity of 0.81 and an excellent AUROC of 0.87. In this sample the prevalence of pregnancy was 16% (95% confidence interval (CI) 13%, 18%) making the PPV 43% and the NPV 95% at this cut-point. The DAP score was the factor most strongly associated with pregnancy, even after age and number of children were taken in to account, with a 78% reduction in the odds of pregnancy for every one-point increase in the DAP (Odds Ratio 0.22 95% CI 0.17, 0.29). The association between baseline DAP score and pregnancy did not differ across time frames. Limitations, reasons for caution: While broadly in line with the UK population in terms of ethnicity, there were small numbers of pregnancies in participants who were from ethnicities other than white. Further work to explore the DAP in non-white ethnicities and languages other than English that are commonly spoken in the UK, as well as exploring pregnancy preferences by sexuality and in people of all genders, will be important next steps, as we did not ask about gender identity. Wider implications of the findings: This is the first study to assess the DAP scale as a screening tool and shows that its predictive ability is superior to the limited pre-existing pregnancy prediction tools. Based on our findings, the DAP could be used with a cut-point selected according to the purpose. Study funding/competing interest(s): The study was funded by an NIHR Advanced Fellowship held by JH (PDF-2017-10-021). The authors declare that they have no conflicts of interest. Trial registration number: n/a

The authors have declared no competing interest.

The study was funded by an NIHR Advanced Fellowship held by JH (PDF-2017-10-021).

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Research Ethics Committee of University College London gave ethical approval for this work (ref 3974.003).

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The dataset is available in the UCL Research Data Repository.