DOPPLER ULTRASOUND IN ASSESSMENT OFFETAL WELLBEING BY DR KH. ELMIZADEH

This technique has been used for studying most of the major fetal circulatory systems, including the umbilical artery ,umbilical vein , aorta , heart, and middle cerebral artery . Doppler sonography provides a unique opportunity to investigate human fetal hemodynamics and to use these findings for fetal surveillance.

Abnormal fetal placental angiogenesis are seen in pregnancies complicated by growth restriction and abnormal umbilical arterial Doppler. These observations suggest fetoplacental vascular maldevelopment results in an increase in impedance that is reflected in the abnormal Doppler waveforms and indices. A change in the Doppler waveform precedes any changes in the fetal heart rate patterns, even with progressive metabolic acidosis.

Obstetrical complications, such as FGR and preeclampsia, result in chronic fetal nutritive and respiratory deprivation. As the stress intensifies and/or lengthens, the fetus mobilizes defensive responses. The primary fetal hemodynamic response to this deprivation involves redistribution of blood flow to the brain, heart, adrenals, and placenta at the expense of flow to muscles, viscera, skin, and other less critical tissues and organs . Doppler ultrasound demonstrates these circulatory changes associated with fetal compromise and allows perinatal prognostication.

Doppler waveform analysis is usually based upon the following characteristics of the maximum frequency shift envelope : ●Peak systolic frequency shift value (S) ●End-diastolic frequency shift value (D) ●Average frequency shift value over the cardiac cycle (A)

The most commonly used obstetrical applications : peak systolic frequency shift to end-diastolic frequency shift ratio (S/D) resistance index :RI= S-D/S pulsatility index: PI = S-D/A

The sequence of changes : Abnormal elevation of Doppler indices ……. loss of fetal heart rate variability and reactivity,,,,,,,,,decline and loss of fetal breathing and body movements. Reversed end diastolic velocity in the umbilical artery, absence or reversed atrial wave in the ductus venosus, and rapid loss of heart rate variability portend a poor outcome. Death occur if there are no interventions. This progression may provide the basis for determining the sequence of fetal testing in clinical practice

AEDV AND REDV   The end-diastolic component of the Doppler waveform is crucial for assessing fetal well-being. Absence of end-diastolic flow velocity (AEDV) or reversal of end-diastolic flow velocity (REDV) is associated with markedly adverse perinatal outcome, particularly a high perinatal mortality rate with a higher prevalence of chromosomal abnormalities (especially trisomy 13, 18, and 21) and congenital anomalies . These relationships are illustrated by the following examples:

●A European multicenter study involving 245 fetuses with AEDV or REDV reported a perinatal mortality rate of 28 percent, and 96 to 98 percent of the infants required intensive care . The risk of cerebral hemorrhage, anemia, and hypoglycemia was also increased.

●A review including 1126 cases of AEDV reported in the literature calculated a stillbirth rate of 170 per 1000 and neonatal mortality rate of 280 per 1000 .Most of the deaths were related to growth restriction, prematurity, fetal anomalies, and aneuploidy.

●A prospective observational study including 113 pregnancies complicated by fetal growth restriction examined the relationship between neurodevelopmental outcome at age 2 and umbilical artery Doppler, ductus venosus Doppler, middle cerebral artery Doppler, as well as the biophysical profile score and several other indicators. Only reverse flow in the umbilical artery, gestational age, and birth weight independently predicted neurodevelopmental delay

The frequency of AEDV is approximately 2 percent in high risk pregnancies and may be as low as 0.3 percent in a general obstetrical population. AEDV may improve over time, although often only transiently, and days to weeks may elapse before the fetus shows additional evidence of compromise, especially in preterm pregnancies. Thus, this finding is not necessarily an immediate indication for delivery in pregnancies before 34 weeks if fetal surveillance tests, such as the NST or biophysical profile, are reassuring. Although delivery after 32 completed weeks of gestation has been recommended, there are continuing concerns about prematurity risks before 34 completed weeks of gestation.

CLINICAL EFFECTIVENESS The benefit of Doppler surveillance primarily pertained to pregnancies complicated by fetal growth restriction or preeclampsia. It may also be useful for fetal surveillance in twin gestations complicated by growth restriction, discordancy, or monochorionicity. Well-designed trials in other populations are needed. UA Doppler as a screening test in low risk pregnancies did not show any improvement in pregnancy outcome.

GUIDELINES FOR CLINICAL PRACTICE UA Doppler assessment is most useful in pregnancies complicated by fetal growth restriction and/or preeclampsia. Doppler velocimetry is recommended as a primary surveillance tool for monitoring these pregnancies .

Clinical interpretation An S/D ratio >3.0 or RI >0.6 at ≥28 weeks of gestation is the best threshold for identifying pregnancies at high risk of adverse outcome . The utility of this technique before 28 weeks for fetal surveillance in high risk pregnancies remains investigational. Gestational age-specific nomogram: DI below the 95th centile for the gestational age should be considered assuring. An initially high S/D ratio may progressively decline with advancing gestation, signifying an improved prognosis. In contrast, a rising UA DI may indicate worsening fetal prognosis.

The most important diagnostic characteristic of the UA Doppler waveform is the state of the end diastolic velocity. AEDV is an ominous finding and should indicate delivery in pregnancies beyond 34 completed weeks. REDV has an even worse prognosis and should be interpreted as a preterminal finding. We feel its presence should indicate immediate delivery as early as 28 weeks of gestation.

Management with normal Doppler indices High risk pregnancies with a DI that remains normal or is not progressively rising should be followed with weekly Doppler evaluation. We use NST or BPP as either a backup test or simultaneously with the UA Doppler. If the fetal and the maternal evaluations remain reassuring, then the pregnancy can continue to 38 to 40 weeks. Growth restricted pregnancies should not continue beyond 40 weeks.

Management with abnormal Doppler indices If the DI is abnormal obstetrical management depends upon : severity of the Doppler abnormality severity of the underlying obstetrical complication duration of gestation presence of Fetal malformations and aneuploidy

A high or increasing DI in the presence of end-diastolic flow weekly umbilical Doppler ultrasound once or twice per week NST, BPP, or modified BPP. If nonreactive NST, poor fetal heart rate baseline variability, persistent late decelerations, oligohydramnios, or BPP score <4 :delivery should be strongly considered.

With development of AEDV or REDV, an urgent clinical response is indicated. the development of AEDV should prompt immediate consideration of delivery if the gestation is beyond 34 completed weeks. The management is more conservative in a more preterm pregnancy (≤34 weeks). In this circumstance, fetal well-being should be assessed daily with UA Doppler, NST, BPP, or modified BPP. Betamethasone should be given. Delivery is indicated when one or more of these tests indicate fetal danger, irrespective of maturity.

Development of REDV at any gestational age beyond 28 weeks should prompt immediate delivery. Some experts would consider continuously monitoring these fetuses and giving a course of betamethasone prior to delivery, and continuing expectant management until 32 weeks as long as fetal surveillance remains reassuring . Use of venous Doppler appears to improve the prediction of stillbirth and acidemia when arterial Doppler has identified a fetus at risk. This is the next step in the evaluation of these fetuses and may help to identify fetuses who require immediate delivery versus those in whom delivery can be delayed.

Mode of delivery In general, cesarean delivery is a reasonable choice in most cases of AEDV, as fetal tolerance to labor is poor in this situation. Cesarean delivery is clearly indicated in the presence of REDV or ominous fetal monitoring findings.

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