Integrating Doppler Ultrasound into Obstetrics Management
Doppler ultrasound has now been used in obstetrics for more than 30 years [1]
[2]. Monitoring of feto-maternal perfusion aims to reduce fetal and perinatal morbidity and mortality, i. e., reduce fetal acidosis, asphyxia and intrauterine fetal death [3]. Compared with many other sonographic procedures, the evidence for obstetric Doppler sonography has been evaluated in randomized trials and backed by well-founded lists of indications [4]. The meta-analyses in the Cochrane Database already showed a significant benefit in the early studies in the group at risk with a reduction in perinatal mortality, caesarean sections, antenatal hospitalizations of pregnant women as well as a reduction in the rate of labor induction [4]
[5]. These effects were detectable in high-risk pregnancies such as maternal diseases (e. g., maternal hypertension, nephropathy, diabetes mellitus, status post preeclampsia, etc.) and fetal risk factors such as intrauterine growth disorders, multiple pregnancies, etc., and have had a significant impact on obstetric decisions. In the following years, questions arose not only about the diagnostic value of Doppler ultrasound in obstetric management, but also about a more differentiated approach to the timing of delivery in term and preterm births. In the 2 randomized TRUFFLE trials, Doppler ultrasound was shown to a) reduce perinatal mortality and morbidity in fetuses with early onset growth restriction, b) significantly improve neurological outcome based on the Bayley assessment at 2 years, and c) play a central role in measuring blood flow in the ductus venosus [6]
[7].
A better neurological outcome after 2 years can be expected if the indication for delivery in a fetus with severe early growth retardation is based on a reversed flow of the A wave of the ductus venosus instead of a change in the Oxford CTG [7].
Recent studies address the questions of the importance of cerebro-placental ratio (CPR) in birth planning in the third trimester and at term [8]. Excessively low CPR values before delivery are associated with a higher rate of impending intrauterine asphyxia, low umbilical cord pH, and a higher rate of transfer to neonatology in growth-retarded fetuses [9]
[10].
In this issue with 3 obstetric Doppler sonography studies, the study by Ortiz et al. shows that low CPR is significantly more likely to be associated with surgical delivery in both growth-retarded and term fetuses. However, the detection rate of high-risk pregnancies was limited, so the authors propose randomized studies with a combination of CPR with maternal, antenatal and intrapartum parameters in order to increase the prognostic value. Mylrea-Foley et al. found in their prospective multicenter study with longitudinal measurements of the UCR (ratio of umbilical and cerebral artery pulsatility index) in fetuses with late growth retardation that repeating the measurements does not increase the predictive value, so that unnecessary follow-up controls are not necessary.
The importance of Doppler ultrasound is also evident during intrauterine surgical procedures [11]. Vonzun et al. demonstrate in their study cohort that the "M sign" in the middle cerebral artery may be an indication of fetal vasoconstriction before and after intrauterine surgery for fetal spina bifida and should be considered in monitoring these fetuses.
Early studies of low-risk cohorts initially failed to demonstrate an advantage of feto-maternal Doppler ultrasound for screening for preeclampsia and growth restriction [12]. It was only when it was shown that aspirin prophylaxis before 16 GW could reduce the risk of preeclampsia in high risk women that the question of screening was raised.
Preeclampsia is a systemic disease and a major cause of maternal and perinatal morbidity and mortality.
Early and late forms can be distinguished distinguished based on the time of manifestation. In particular, early PE before ≤ 34 + 0 GW (early-onset preeclampsia) but also later PE between 34 and 37 GW (late preterm preeclampsia) may be associated with severe progression and preterm birth. Beyond the immediate peripartum complications, they are also associated with significant long-term morbidity for both mother and child [13].
Various screening models have been developed; the most accepted and widely used method is the Fetal Medicine Foundation (FMF, London, UK [14]) PE screening, which calculates a woman's risk of developing PE during her pregnancy in the first trimester (GW 11 + 0–13 + 6). This screening test has also been prospectively validated in different populations [15]. This combines the a priori risk from maternal characteristics and medical history data with biophysical (mean arterial blood pressure (MAP) and Doppler of the uterine arteries (UtA-PI)) and biochemical parameters (placental growth factor, PLGF). In addition to the high detection rate, the screening algorithm also has a high negative predictive value for early PE as well as for the development of fetal growth restriction [16].
The combination of a screening test with aspirin prophylaxis started before 16 GW can reduce the risk of PE before 37 GW by 62 % [17].
The test performance of the PE screening test is highest when all biomarkers are included in the risk calculation. In this context, the measurement of UtA-PI is one of the main elements in the PE screening algorithm. Of all the PE biomarkers, UtA-PI is the most user-dependent. Regular quality controls are therefore of essential importance. This could also be shown in a large retrospective cohort study with 21,010 pregnant women: 97 % of the sonographers trained in PE screening achieved UtA-PI values within acceptable values between 0.90 and 1.10 MoMs [18].
In addition to the direct positive impact of the PE prevention model on the course and outcome of pregnancy, screening additionally offers the potential to reduce the extended consequences of PE. The long-term consequences of preeclampsia on the future life and health of the pregnant woman and the child have been clearly described and are well known [13]. These complications could be avoided by preventing preeclampsia. This would be generationally beneficial and also of considerable health economic interest.
In summary, Doppler sonography has been widely established not only in the management of high-risk pregnancies but also in screening for pregnancy complications. The list of indications could be extended, such as in the detection of certain fetal malformations.
In clinical practice, Doppler ultrasound defines the management of high risk pregnancies and is the most improtant tool in the decision making process. This applies to traditional obstetric issues such as outpatient care vs. hospitalization and determining the appropriate time of delivery with the goal of reducing perinatal mortality and morbidity in addition to improving the neurological outcome of infants. However, Doppler ultrasound is also essential for the management of pregnancies with an unremarkable risk profile.
Thus, feto-maternal Doppler ultrasound is not only a diagnostic tool in obstetrics, but also has a crucial impact on our therapeutic approach. In addition, there is the prospect of significantly reducing maternal morbidity rates from preeclampsia. World-wide the incidence of preeclampsia varies from 2 % to 8 % [19]. It is suggested that over 90 % of maternal deaths from preeclampsia/eclampsia in Europe would be preventable [20]. This would achieve an essential goal of a screening examination in general, namely the achievement of a therapeutic benefit as a result.
