Fig 1. Threshold number needed to prevent (NNP_T) at varying quality-adjusted life years (QALYs) gained per preeclampsia event avoided.

NNP_T calculated as: (QALYs gained x $50000) / DC [24], assuming a direct cost (DC) of ASA of $10 per pregnancy. The dashed blue lines show that, at 0.52 QALYs gained by ASA prophylaxis [1], a clinician would be willing to give ASA prophylaxis to as many as 2600 women—the NNP_T. For a more modest amount of 0.05 QALYs gained, the NNP_T would be 250 (dashed red lines). The NNP_T is presented on a log₂ scale for ease of viewing.