The first trimester uterine artery Doppler: comparison between sagittal and transverse techniques

First trimester preeclampsia screening and prediction

Preeclampsia is a major cause of maternal and perinatal morbidity and mortality. Early-onset disease requiring preterm delivery is associated with a higher risk of complications in both mothers and babies. Evidence suggests that the administration of low-dose aspirin initiated before 16 weeks' gestation significantly reduces the rate of preterm preeclampsia. Therefore, it is important to identify pregnant women at risk of developing preeclampsia during the first trimester of pregnancy, thus allowing timely therapeutic intervention. Several professional organizations such as the American College of Obstetricians and Gynecologists (ACOG) and National Institute for Health and Care Excellence (NICE) have proposed screening for preeclampsia based on maternal risk factors. The approach recommended by ACOG and NICE essentially treats each risk factor as a separate screening test with additive detection rate and screen-positive rate. Evidence has shown that preeclampsia screening based on the NICE and ACOG approach has suboptimal performance, as the NICE recommendation only achieves detection rates of 41% and 34%, with a 10% false-positive rate, for preterm and term preeclampsia, respectively. Screening based on the 2013 ACOG recommendation can only achieve detection rates of 5% and 2% for preterm and term preeclampsia, respectively, with a 0.2% false-positive rate. Various first trimester prediction models have been developed. Most of them have not undergone or failed external validation. However, it is worthy of note that the Fetal Medicine Foundation (FMF) first trimester prediction model (namely the triple test), which consists of a combination of maternal factors and measurements of mean arterial pressure, uterine artery pulsatility index, and serum placental growth factor, has undergone successful internal and external validation. The FMF triple test has detection rates of 90% and 75% for the prediction of early and preterm preeclampsia, respectively, with a 10% false-positive rate. Such performance of screening is superior to that of the traditional method by maternal risk factors alone. The use of the FMF prediction model, followed by the administration of low-dose aspirin, has been shown to reduce the rate of preterm preeclampsia by 62%. The number needed to screen to prevent 1 case of preterm preeclampsia by the FMF triple test is 250. The key to maintaining optimal screening performance is to establish standardized protocols for biomarker measurements and regular biomarker quality assessment, as inaccurate measurement can affect screening performance. Tools frequently used to assess quality control include the cumulative sum and target plot. Cumulative sum is a sensitive method to detect small shifts over time, and point of shift can be easily identified. Target plot is a tool to evaluate deviation from the expected multiple of median and the expected median of standard deviation. Target plot is easy to interpret and visualize. However, it is insensitive to detecting small deviations. Adherence to well-defined protocols for the measurements of mean arterial pressure, uterine artery pulsatility index, and placental growth factor is required. This article summarizes the existing literature on the different methods, recommendations by professional organizations, quality assessment of different components of risk assessment, and clinical implementation of the first trimester screening for preeclampsia.

Effects of early aspirin therapy on utero-placental hemodynamics in patients at risk of preeclampsia

OBJECTIVES

To evaluate the effects of early aspirin therapy on the mean pulsatility index of both uterine arteries (utA PI) at 1st and 2nd trimester in women at risk of preeclampsia (PE).

METHODS

Uterine artery (utA) blood flow characteristics were obtained in 315 women, 73 women at risk for PE and early aspirin treatment (group 1), 124 without specific risk factors and no aspirin treatment (group 2) and 118 women with manifest PE (group 3). Mean utA PI of group 1 and group 2 were compared within and between the groups at the 1st and 2nd trimester time points. Furthermore, values at 2nd trimester were compared with those of group 3. Observed to expected mean utA PI ratio (O/E ratio) were calculated for comparison between the groups.

RESULTS

Mean utA PI of group 1 was significantly higher in the 1st trimester compared to group 2 (1.74 vs. 1.47, p = .0117). In the 2nd trimester mean PI decreased significantly in both groups from 1.74 to 1.16 in group 1 and from 1.47 to 0.90 in group 2 (p < .0001). Nevertheless, the difference between the groups was significantly higher in the 2nd trimester than in the 1st trimester (0.29 vs. 0.27, p < .001). Correction for gestational age by analyzing mean utA O/E ratios showed a comparable pattern with a significantly decrease in both groups (1.40 to 1.10 in group 1 and 1.18 to 0.78 in group 2, p < .0001), but a significant higher decrease in the 2nd trimester in group 2 (0.31 vs.0.22, p < 0001). The prevalence of PE was 15.1% (11/73) in group 1 (4 early/7 late onset PE) and 4.7% (6/124) in group 2 (1 early/5 late onset). Mean utA PI and O/E ratio obtained in the 2nd trimester were higher in all PE cases with no significant difference between early and late onset PE (1.49/1.57 and 1.25/1.36 in group 1 and 0.80/0.97 and 0.77/0.99 in group 2). However, mean utA PI and O/E ratio decreased in all cases without PE in both groups, whereas mean utA PI was 1,37 and O/E-ratio was 1,29 in patients with manifest PE at admission, with significantly higher values in early onset than in late onset PE (1.45/1.31 vs. 1.07/1.02, p < .0001).

CONCLUSIONS

Our results show that early aspirin treatment leads to a decrease of elevated mean utA PI between 1st and 2nd trimester in patients at elevated risk for PE which is inferior to the decrease observed in women at standard risk for PE. While aspirin improves trophoblast invasion during early second trimester, vascular resistance remains well above average levels. Limited vascular remodeling capacity in the utero-placental perfusion area seems to be the explanation why aspirin does not abrogate PE in all women and has little effect on birth weight. Another explanation might be that a dose of 100 mg aspirin was used as compared to the 150 mg which is recommended today. Our findings underscore the need to study the effects of intervention already during the early stages of trophoblast invasion in the first trimester.