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Chapter 23
Doppler Velocimetry in Prolonged Pregnancy
Ray O. Bahado-Singh, Maria Segata, Chin-Chien Cheng, Giancarlo Mari
Introduction
Registry data [1] indicate that the increased risk of
stillbirth in post-term pregnancies is partly due to an
increased risk of small-for-gestational-age (SGA) fetuses;
the latter is in turn partly due to an increased
risk of congenital anomalies. When malformations
were excluded, the post-term SGA had a higher stillbirth
rate than term SGA and post-term appropriatefor-gestational-age
fetuses. Similarly, the risk of 5-min
Apgar score < 5 was higher among the post-term SGA
than the other two groups. Naeye [2] estimated that
50% of the excess perinatal mortality in post-term
pregnancy was due to problems related to uteroplacental
perfusion inadequacy (25%) or congenital malformations
(25%).
As a result of data indicating an elevated risk of
adverse perinatal outcomes, antenatal testing is now a
standard feature of the clinical management of prolonged
gestations [3]. There is convincing scientific
evidence that Doppler velocimetry of the umbilical
vessels identifies uteroplacental insufficiency in highrisk
pregnancies. Furthermore, it has been shown
that when umbilical Doppler information is made
available to clinicians it improves decision making
and ultimately the outcomes in such pregnancies [4].
Not surprisingly, therefore, there was initial interest
and optimism in deploying Doppler for the management
of prolonged gestation.
Whether or not umbilical Doppler velocimetry
proves to be beneficial depends on a single overriding
consideration, namely, the pathological basis of poor
perinatal outcome in prolonged gestations. The answer
to this question remains unresolved. If uteroplacental
vascular insufficiency is the principal cause of
poor outcome, then it is reasonable to expect that
umbilical artery Doppler will identify the prolonged
pregnancies destined for poor outcome; if not, then
Doppler is likely to be of little value in clinical management.
Umbilical Artery Doppler
In one of the earliest studies, Rightmire and Campbell
[5] prospectively evaluated the umbilical artery
Pourcelot index (PI) in 35 singleton pregnancies between
42 and 44 2/7 weeks' gestation. A ªlabor-compromisedº
fetus was defined as one with either Apgar
score