OBJECTIVE: Efficient prenatal risk communication hinges upon parents' grasp of statistical information. When forming their subjective representation of a probability, pregnant women may focus on inappropriate factors and ignore the appropriate factors. METHOD: The present research investigates the subjective probability that pregnant women derive from statements of the form 'There is a 1 in X chance that the baby will have condition Y,' where the number X and the severity of the condition Y were orthogonally manipulated. RESULTS: Study 1 showed that when judging how big is a 1 in X chance that a child will be affected by condition Y, pregnant women (n = 336) were sensitive to the severity of Y, but selectively numb to the objective number X. Study 2 (n = 461) replicated this pattern, but also showed that numerical numbness could be overcome by a simple intervention, namely, a quick comment that 1 in X was 'above average.' CONCLUSION: Practitioners must be aware that when forming a subjective probability assessment, pregnant women might be inappropriately sensitive to the severity of Y, and inappropriately numb to the number X, and that a simple communicative intervention can help in overcoming this selective number numbness.