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.