Preeclampsia Prevention by Timed Birth at Term

Most preeclampsia occurs at term. There are no effective preventative strategies. We aimed to identify the optimal preeclampsia screening and timing of birth strategy for prevention of term preeclampsia. METHODS: This secondary analysis was of data from a prospective nonintervention cohort study of singleton pregnancies delivering at ≥24 weeks, without major anomalies, at 2 United Kingdom maternity hospitals. At routine visits at 11 to 13 weeks’ (57 131 pregnancies screened, 1138 term preeclampsia developed) or 35 to 36 weeks’ gestation (29 035 pregnancies screened, 619 term preeclampsia), with patient-specific preeclampsia risks determined by: United Kingdom National Institute for Health and Care Excellence guidance, and the Fetal Medicine Foundation competing-risks model. For each screening strategy, timing of birth for term preeclampsia prevention was evaluated at gestational time points that were fixed (37, 38, 39, 40 weeks) or dependent on preeclampsia risk by the competing-risks model at 35 to 36 weeks. Main outcomes were proportion of term preeclampsia prevented, and number-needed-to-deliver to prevent one term preeclampsia case. RESULTS: The proportion of term preeclampsia prevented was the highest, and number-needed-to-deliver lowest, for preeclampsia screening at 35 to 36 (rather than 11–13) weeks. For delivery at 37 weeks, fewer cases of preeclampsia were prevented for National Institute for Health and Care Excellence (28.8%) than the competing-risks model (59.8%), and the number-needed-to-deliver was higher (16.4 versus 6.9, respectively). The risk-stratified approach (at 35–36 weeks) had similar preeclampsia prevention (by 57.2%) and number-needed-to-deliver (8.4), but fewer women would be induced at 37 weeks (1.2% versus 8.8%). CONCLUSIONS: Risk-stratified timing of birth at term may more than halve the risk of term preeclampsia.