Objective: Investigate cost effectiveness of first trimester preeclampsia screening using the Fetal Medicine Foundation (FMF) algorithm in comparison to standard care. Design: Retrospective observational study Setting: London tertiary hospital Population: 5957 pregnancies screened for preeclampsia using the National Institute for Health and Care Excellence (NICE) method. Methods: Differences in pregnancy outcomes between those who developed preeclampsia, term preeclampsia and preterm preeclampsia were compared by the Kruskal-Wallis and Chi-square tests. The FMF algorithm was applied retrospectively to the cohort. A decision analytic model was used to estimate costs and outcomes for pregnancies screened using NICE and those screened using the FMF algorithm. The decision point probabilities were calculated using the included cohort. Main outcome measures: Incremental healthcare costs and QALY gained per pregnancy screened. Results: Of 5957 pregnancies, 12.8% and 15.9% were screen positive for the development of preeclampsia using the NICE and FMF methods, respectively. Of those screen positive by NICE recommendations, aspirin was not prescribed in 25%. Across the three groups: pregnancies without preeclampsia, term preeclampsia and preterm preeclampsia, respectively there was a statistically significant trend in rates of emergency caesarean (21%, 43%, 71.4%; p=<0.001), admission to neonatal intensive care unit (NICU) (5.9%, 9.4%, 41%; p=<0.001) and length of stay in NICU. Use of the FMF algorithm was associated with 7 fewer cases of preterm preeclampsia, cost saving of £9.06 and a QALY gain of 0.00006/pregnancy screened. Conclusions: In our cohort, using a conservative approach, application of the FMF algorithm achieved clinical benefit and an economic cost saving.