Prevalence of PrE in the index study was 7.6%.
There was significant association between S/D ratio result and development of pre-eclampsia (p= 0.003).
The specificity was higher (88% vs.78%),
while the sensitivity was lower (46.2% vs.
71%) than reported by Madazli et al.[7] These differences may be due to much higher prevalence of PrE (11.5%) in their studied population or defining differently an abnormal result as S/D >2.6.
Mean RI showed no significant association with development of pre-eclampsia and is consonant with findings by Naategaal[8] in Australia. In contrast,
Rampello et al[9] in Italy reported significant association between RI and PrE.
This variation may be due to the fact that they studied a high-risk population of Caucasian women.
Specificity,
PPV and NPV were similar,
but the sensitivity was lower than reported in another study by Parretti et al[10] and may be due to different cutoff (RI>0.58) they used.
Mean PI >95th centile was strongly associated with development of pre-eclampsia (p= 0.00) in the index study and is similar to the findings by Cooley et al[11] and Lopez-Mendez et al[5]. For prediction of PrE,
mean PI alone had a modest sensitivity of 38.5% and PPV of 41.7% respectively,
with high specificity 96%.
These findings are similar to those reported by Jamal et al.[12] Noor et al[13] found a higher sensitivity.
Again,
the differences in cut-off values and prevalence of PrE may account for these variations.
No significant association between bilateral notching and PrE was found. This contrasts with the findings of Asnafi et al[14] in Iran who reported significant association of PrE with uterine artery notching. This difference may be because their study was done in a high-risk cohort with a higher prevalence of PrE compared to our unselected study population.
Uterine artery notching gave sensitivity of 23.1%,
specificity of 92.9%,
PPV of 21.4% and NPV of 93.6% for PrE.
The sensitivity and specificity are similar to findings by Audibert et al[15] and Espinoza et al[16] in the USA but is lower than those from other studies in low risk populations.[17,18] These variations may be due to difference in study design or racial differences.
The accuracy of various indices for prediction of PrE was compared using ROC curves. The combined test result had the highest performance with an Area under the curve (AUC) of 0.71 (95% CI: 0.534 - 0.871) This is similar to findings by Lopez-mendez et al[5] who reported that a combined abnormal result (combination of a proto-diastolic notch and RI + PI >95th centile) gave the highest predictive accuracy. Our finding that RI >95th centile performed poorly varied from the findings of Aqualina et a[19] who reported the best screening method as a combination of mean RI with bilateral notching.
This difference may be due to their use of mean RI as cutoff compared to RI > 95th centile used in the index study.
Espinoza et al[16] found Bilateral UtA notching and a mean UtA PI>95th percentile had the highest AUC for the prediction of PrE.
This difference may have arisen due to the poor association of uterine artery notching with pre-eclampsia in our study (AUC= 0.58,
p=0.317) and thus was minimally helpful in combination with other poorly performing indices for identifying patients who are likely to develop PrE.
All Doppler indices except uterine notching were significantly associated with severe PrE. The sensitivity for detection of severe PrE increased from 38.5% to 75% and 23.1% to 60% for PI and RI respectively and is consistent with findings from previous studies.[20] Accuracy of all the indices were better for prediction of severe PrE as evidenced by the increase in the AUC.
In conclusion,
UtAD showed limited value in identifying patients destined to develop pre-eclampsia and may be incorporated into the routine anomaly scan.
Women with a normal screening Doppler would not require further assessment while women with abnormal UtAD may benefit from a follow up Doppler examination,
as the persistence of these abnormalities may increase accuracy of the Doppler indices.
Further study of the predictive role of uterine Doppler indices among women with high risk pregnancies in our environment is recommended.