Abstract: Background. Standard medical-decision making models generally incorporate the best known probabilities regarding the risks and benefits from various treatments and interventions, patient preferences or utilities to generate quality-adjusted life years (QALYs), and exponential discounting to modify preferences over time. However, work in behavioral economics has demonstrated that individuals themselves do not seem to simply utilize probabilities as given, but may bias them away from the best known probability using a weighting function. They also are unlikely to discount exponentially, but rather in some hyperbolic form. A two-parameter discounting model, present-biased preferences, has been proposed in the behavioral economics literature. The two parameters include, β, which is the difference in valuation between today and the short-term future, and δ, which functions similarly to that in exponential discounting. Methods. Utilizing estimates of risk perception from a linear scale and estimates from standard gamble (SG) and time-tradeoff (TTO) utilities regarding two outcomes, Down syndrome and procedure-related miscarriage, the departures from standard medical-decision making models were examined. For risk perception, perceived risk was compared to known risk and the associations with individual characteristics were examined. For discounting, it was assumed that measured preferences from SG and TTO should be similar for the same outcome for a given individual. Given this, the discount rate that would equalize the measured results from TTO and SG was determined in both the exponential and the present-biased preference discounting models. Finally, both the perceived risk and discounting models were examined in decision analytic models to determine the effect that they could have on decision-making in the setting of prenatal diagnosis. Results/Conclusions. Factors which are not associated with actual risk of Down syndrome or procedure-related miscarriage were found to be associated with perceived risk of these events including: maternal race/ethnicity, education, income, health status, and inclination towards prenatal diagnosis. Additionally, the two parameter model could more consistently model the time discounting in these measured preferences. While exponential discounting has been the standard, present-biased preferences may better represent individuals' preferences over time. In decision-analytic models, both of these deviations led to changes in optimal decision-making.