OBJECTIVE: To assess the effects of sociodemographic and health-provider factors on women's understanding of abnormal results on measurement of nuchal translucency (NT) and maternal serum screening (MSS), 18 months after the implementation of a policy aimed at increasing women's awareness regarding MSS. METHODS: A representative sample of women (n = 734) who gave birth in Parisian maternity units in 1999 were asked about their understanding of an abnormal result on MSS and NT. We assessed the effects of sociodemographic and health-provider factors on the probability of women interpreting an abnormal result correctly, misinterpreting it as a definitive diagnosis, or declaring that they did not know how to interpret the result. Response rate was 92% and the analyses included multinomial models. RESULTS: For both MSS and NT measurement, the majority of women interpreted an abnormal result correctly. However, there were substantial sociodemographic differences in the probability of women interpreting an abnormal result correctly, and more so in the probability of their declaring not to know how to interpret the result. The probability of correct interpretations was substantially higher, and that of declaring not to know how to interpret the result substantially lower, for MSS than NT measurement. However, for several sociodemographic groups, the proportion of women who misinterpreted an abnormal result on screening as indicative of a definitive diagnosis was also higher for MSS as compared with NT measurement. CONCLUSIONS: These findings underscore the need for additional efforts, along with alternative strategies, to inform women about the implications of prenatal screening, particularly in the case of measurement of NT.