Study question: What are the factors influencing couples' preferences for fresh versus elective frozen embryo transfer (ET) in in-vitro fertilisation (IVF)?Summary answer: Accepting that elective frozen ET can delay treatment but reduces the risk of OHSS, couples' choices are driven by expected pregnancy and birth outcomes. What is known already: Elective frozen embryo transfer results in livebirth rates which are on par with, or better than those following fresh embryo transfer. In terms of safety, elective embryo transfer reduces the risk of ovarian hyperstimulation (OHSS) and small for gestational age babies but increases the risk of pre-eclampsia and large for gestational age compared to fresh embryo transfer. Given the prevailing uncertainty around a universal policy of elective frozen embryo transfer for all couples undergoing IVF, user preferences are critical in informing clinical decision making. Study design, size and duration: Discrete choice experiments (DCEs) are a preference elicitation technique for assessing the value that individuals derive from different aspects of a treatment or service. We asked both partners of 104 IVF naïve couples attending a tertiary referral centre to independently complete a questionnaire with nine hypothetical choices illustrating potential advantages and disadvantages of fresh versus frozen embryo transfers in terms of four attributes (live birth rate, miscarriage rate, neonatal complication rate and cost of treatment). Participants/materials, setting, and methods: Participants were informed that frozen ET would delay the transfer of embryos by 6-8 weeks but reduce the risk of OHSS. An opt-out(no IVF treatment) was included for each choice task. Logistic regression was used to analyse the choice response data and estimate preference weights for fresh and frozen ET and each treatment attribute. Willingness to pay (WTP) was calculated as the marginal rate of substitution between the cost attribute and each other attribute. Results A total of 104 couples completed 208 questionnaires. Couples preferred both fresh and elective frozen embryo (Odds ratio 27.65 and 27.7 respectively) compared to no IVF treatment with no strong preference for fresh over frozen. Couples strongly preferred any IVF technique that offered an increase in live birth rates by 5% OR 1.28 (95% CI; 1.07 to 1.53), reduced miscarriage by 18% OR 0.54 (95% CI; 0.45 to 0.63) and diminished neonatal complications by 10% OR 0.59 (95% CI; 0.50 to 0.70). Respondents were willing to pay an additional £2452 (95% CI; 596 - 4,308) and £7,168 (95% CI 5,053 - 9,283) for a 5% and 15% increase in live birth respectively regardless of whether this involved fresh or frozen embryos. They required compensation of £5,230 (95% CI; 3,320 -7,141) and £13,245 (95% CI; 10,110 - 16,380) for treatments that increase the neonatal complication rate by 10% and 25% respectively. Couples valued a 10% diminution in the risk of neonatal complications and a 10% increase in live birth rates equally. Older women put a higher monetary value on live birth rate than younger women. Partners tended to place greater value on reductions in treatment associated risks than those intending to get pregnant. Limitations, reasons for caution: DCEs can elicit intentions which may not reflect actual behaviour. The external validity of this study is limited by the fact that it was conducted in a single centre with generous public funding for IVF. Wider implications of the findings: Couples undergoing IVF may be willing to forgo higher livebirth rates in order to reduce maternal and perinatal risks. Along with evidence from randomised trials, these preferences should be used to inform policy as well as individualised decision making in IVF.