Development of pre-eclampsia within 4 weeks of sFlt-1/PlGF ratio > 38: comparison of performance at 31-34 vs 35-37 weeks' gestation

Objective: To compare the performance of screening by soluble fms-like tyrosine kinase 1 (sFlt-1) to placental growth factor (PlGF) ratio > 38 for the prediction of delivery with pre-eclampsia (PE) at < 1 week and < 4 weeks from assessment when the test is carried out at 31-34 vs 35-37 weeks' gestation.

Methods: This was a prospective observational study in women attending a third-trimester ultrasound scan as part of routine pregnancy care; the visit was at 30-34 weeks' gestation in the first phase of the study and at 35-37 weeks in the second phase. Serum sFlt-1 and PlGF were measured and their ratio calculated. We estimated the detection rate (DR) and false-positive rate (FPR) of sFlt-1/PlGF ratio > 38 for predicting delivery with PE at < 1 week and < 4 weeks after assessment and compared the performance of screening when the test was carried out at 31 + 0 to 33 + 6 vs 35 + 0 to 36 + 6 weeks' gestation.

Results: The study population included 8063 singleton pregnancies that were examined at 31-34 weeks and 3703 at 35-37 weeks. Delivery with PE occurred at < 1, < 4 and ≥ 4 weeks from assessment in five (0.1%), 29 (0.4%) and 202 (2.5%) women assessed at 31-34 weeks, respectively, and in seven (0.2%), 39 (1.1%) and 21 (0.6%) of those assessed at 35-37 weeks. In women without PE, the median sFlt-1/PlGF ratio increased with gestational age at screening and a ratio of 38 was just below the 99^th percentile at 32 weeks' gestation and just below the 90^th percentile at 36 weeks. In the two gestational windows, the DR of PE delivering < 4 weeks from assessment was similar (75.9% (95% CI, 56.5-89.7%) vs 79.5% (95% CI, 63.5-90.7%)), but the FPR was substantially lower at 31-34 weeks than at 35-37 weeks (1.7% (95% CI, 1.4-2.0%) vs 9.6% (95% CI, 8.7-10.6%)). The number of cases with PE delivering < 1 week from assessment was small, but similarly, in the two gestational windows, the DR was comparable (80.0% (95% CI, 28.4-99.5%) vs 85.7% (95% CI, 42.1-99.6%)), and the FPR was substantially lower at 31-34 weeks than at 35-37 weeks (1.9% (95% CI, 1.6-2.2%) vs 10.2% (95% CI, 9.3-11.3%)).

Conclusion: The performance of sFlt-1/PlGF ratio > 38 in the prediction of delivery with PE at < 1 and < 4 weeks from assessment is substantially different when the assessment is at 31-34 weeks' gestation compared to at 35-37 weeks. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.