With this technique, early changes in placenta-based growth restriction are detected in peripheral vessels such as the umbilical and middle cerebral arteries. Late changes are characterized by reversal of umbilical artery flow and by abnormal flow in the ductus venosus and fetal aortic and pulmonary outlow tracts.
Of these, abnormal umbilical artery Doppler velocimetry indings-characterized by absent or reversed end-diastolic low-are uniquely linked with fetal-growth restriction (Chap. 10, p. 213). hese abnormalities highlight early versus severe growth restriction and represent the transition from fetal adaptation to failure. Thus, persistently absent or reversed end-diastolic flow, such as that shown in Figure 44-8, has long been correlated with hypoxia, acidosis, and fetal death. In one prospective sonographic examination of 1116 fetuses with estimated fetal weights < 10th percentile, only 1.3 percent of fetuses with normal umbilical artery Doppler studies had adverse outcomes compared with 11.5 percent of those with Doppler abnormalities (O'Dwyer, 2014). Unterscheider and associates (2013a) reported that abnormal umbilical artery Doppler velocimetry combined with an estimated fetal weight <3rd percentile is most strongly associated with poor obstetrical outcome.
FIGURE 44-8 Doppler velocity waveforms. A. Normal waveform with normal SID ratio. B. Increased impedance to flow with abnormally elevated SID ratio. C. Absent end-diastolic flow. D. Reversed end-diastolic flow.
Because of these findings, umbilical artery Doppler velocimetry is considered standard in the evaluation and management of the growth-restricted fetus. he American College of Obstetricians and Gynecologists (2015) has concluded that umbilical-artery Doppler velocimetry improves clinical outcomes. It is recommended in the management of fetal-growth restriction as an adjunct to standard surveillance techniques such as nonstress testing and biophysical proile.
Other Doppler assessments are still investigational. Interrogation of the ductus venosus was evaluated in a series of 604 fetuses <33 weeks' gestation who had an abdominal circumference <5th percentile (Baschat, 2007). Ductus venosus Doppler parameters were the primary cardiovascular factor in predicting neonatal outcome. These late changes are felt to relect myocardial deterioration and acidemia, which are major contributors to adverse perinatal and neurological outcome. In another study of 46 growth-restricted fetuses, Doppler flow abnormalities of the aortic valve isthmus preceded those in the ductus venosus by 1 week (Figueras, 2009). In their evaluation of several fetal vessels, Turan and associates (2008) described the seq uence of changes characteristic of mild placental dysfunction, progressive placental dysfunction, and severe, early-onset placental dysfunction. However, Unterscheider and colleagues (2013b) questioned whether a predictable progression of Doppler indices actually exists in fetal-growth restriction.
Fetal-growth restriction prevention ideally begins before conception. Maternal medical conditions, medications, and nutrition are optimized, and smoking cessation is critical. Other risk factors are tailored to the maternal condition, such as antimalarial prophylaxis for women living in endemic areas and correction of nutritional deficiencies. Of note, treatment of mild-to-moderate hypertension does not reduce the incidence of growth-restricted newborns (Chap. 50, p. 981).