Clinical implications
The advantage of using the sFlt-1/PlGF ratio cut-off of 38 is the ease of interpretation if negative. Then ambulatory management and repeated pre-eclampsia markers assessment in more than one week if suspicion persists seems a safe approach, as no event has been observed in these groups (309 assessments). On the other hand, pregnancies with an sFlt-1/PlGF ratio above 38 require a more complex assessment and 16.9% (36/213) of assessments obtained a positive result with the prognostic assessment tool. The prognostic assessment tool reached a positive predictive value of 77.8%, which compared with the positive predictive value of the sFlt-1/PlGF ratio cut-off of 38 (22.1%) indicates its value as a confirmatory test. However, in approximately 85% of occasions, the prognostic assessment tool resulted negative and no position can be recommended for these pregnancies as 10.7% of them (19/177) delivered due to early-onset pre-eclampsia within one week. Once externally validated, this prognostic prediction tool may allow induced delivery indication and planning of adequate maternal and neonatal care in test positive pregnancies.
As proangiogenic and antiangiogenic markers vary with gestational age in healthy pregnancies, the predictive ability of those markers should benefit from MoM transformation (26). Besides, the ratio between markers with unequal discriminatory power is likely to be misleading, suboptimal and unnecessary (27-28). Moreover, we did not observe any obvious advantage in using raw sFlt-1/PlGF ratio values when above 38.
Costs of NT-proBNP inclusion can be balanced with the withdrawal of repeated PlGF determinations in pregnancies with clinical suspicion of early-onset pre-eclampsia and a previous sFlt-1/PlGF ratio above 38.
PlGF-based tests are also used to assist ruling out a diagnosis of pre-eclampsia in women presenting with suspected pre-eclampsia. PlGF levels above 100 pg/mL have been described as suggestive of patients without placental dysfunction who are unlikely to progress to delivery within 14 days from testing (29). The application of a PlGF cut-off value of 100 pg/mL to our study would omit 4.26% (2 out of 47) of pregnancies with early-onset pre-eclampsia leading to delivery within seven days of testing. Cut-off values above 150 pg/mL showed similar results to an sFlt-1/PlGF ratio cut-off of 38.