OBJECTIVE To evaluate a soluble fms-like tyrosine kinase-1 (sFlt-1) to placental growth factor (PlGF) ratio cut-off of 38 for the prediction of pre-eclampsia (PE) in routine assessment in singleton pregnancies at 30-37 weeks' gestation. METHODS This was a prospective observational study in women attending a third-trimester ultrasound scan at 30-37 weeks as part of routine pregnancy care. Serum sFlt-1 and PlGF were measured and their ratio was calculated. We estimated the detection rate (DR), false-positive rate (FPR), positive predictive value (PPV) and negative predictive value (NPV) of sFlt-1/PlGF ratio >38 for the prediction of delivery with PE at < 1, < 4 and ≥ 4 weeks after assessment. RESULTS The study population of 12 305 singleton pregnancies was examined at a median of 32.4 (range, 30.0-36.9) weeks and included 14 (0.11%), 77 (0.63%) and 227 (1.84%) cases that subsequently delivered with PE at < 1, < 4 or ≥ 4 weeks' after assessment, respectively. The DR, FPR, PPV and NPV of sFlt-1/PlGF ratio > 38 in the prediction of delivery with PE at < 1 week were 78.6%, 4.5%, 1.9% and 99.97%, respectively; the values for delivery with PE at < 4 weeks were 76.6%, 4.1%, 10.4% and 99.85% and for delivery with PE ≥ 4 weeks were 20.7%, 4.3%, 8.3% and 98.47%. CONCLUSION In routine screening of singleton pregnancies, the performance of a sFlt-1/PlGF ratio > 38 is modest for the prediction of delivery with PE at < 1 and at < 4 weeks after assessment and poor for the prediction of delivery with PE at ≥ 4 weeks after assessment. A sFlt-1/PlGF ratio > 38 predicted 79% of cases delivering with PE at < 1 week after assessment, at a FPR of 4.5%; consequently, a policy of hospitalizing patients with a ratio > 38 would potentially lead to unnecessary hospitalization in 4.5% of pregnancies and a ratio of ≤ 38 would falsely reassure one fifth of women who will deliver with PE within 1 week of assessment. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.