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.
