o_1977r8vv9vk1ts2ms0kd8pksa.pdf

358 R. O. Bahado-Singh et al.
ing in oligohydramnios. Bar-Hava et al. [20] found
no such difference in the middle cerebral artery RI
when a group of 15 post-term fetuses with oligohydramnios
was compared with 42 with normal fluid
volume defined as amniotic fluid indexes >5 cm. As
mentioned previously, the study by Devine et al. [17]
found cerebral redistribution defined as middle cerebral
artery umbilical artery Doppler ratio < 1.05 to be
reduced in compromised post-term pregnancies. This
ratio was found to be a significant predictor, with
80.0% sensitivity and 94.9% specificity for the detection
of adverse outcomes in such fetuses. Zimmerman
et al. [14] did not find significant differences in the
middle cerebral Doppler RI values when subgroups of
post-term patients with complications such as low
Apgar scores, low cord pH, postmaturity syndrome,
or thick meconium, among others, were compared
with a normal group. No power analysis was performed
to determine adequacy of the sample size. It
is likely based on numbers presented that the study
was underpowered for these analyses. Selam et al.
[21] studied the middle cerebral artery PI in 10 postterm
cases with amniotic fluid index > 5 cm compared
with 25 cases with normal fluid. The middle
cerebral artery PI was significantly lower in the postterm
group with oligohydramnios (median value 0.89
vs 1.33, respectively; p=0.004). The placental±cerebral
ratio derived as umbilical to middle cerebral PI value
was significantly higher in the oligohydramnios vs
normal fluid group (median value 0.88 vs 0.67, respectively;
p=0.027). This supports the notion that
cardiovascular redistribution occurs in pregnancies
complicated by oligohydramnios.
The study by Brar et al. [22] also found reduced
cerebral placental (umbilical) S/D ratios in 19 postterm
patients with abnormal antepartum test defined
as either an abnormal NST or amniotic fluid index
< 5 cm compared with a group of 26 with normal test
results. Cerebral to placental resistance in the compromised
group was 1.1Ô0.3 vs 1.8Ô0.3 in normal
(p 41
weeks. Time-averaged velocity of the descending thoracic
aorta was significantly decreased in cases with
meconium, moderate to severe variable decelerations
and operative delivery for fetal distress compared
with their unaffected peers. Olofsson et al. [23] compared
mean thoracic aortic Doppler velocities and estimated
aortic blood flow using vessel diameter measurements
in 34 women delivered after 43 weeks
compared with 32 controls delivered 41 weeks
who had either normal or reduced amniotic fluid volume.
The 16 post-term cases with low AFI (< 5 cm)
had significantly worse perinatal outcome including
cesarean section for fetal distress, NICU admission,
and 5-min Apgar score < 7 when compared with the
post-term group with normal fluid volume.
The cumbersome and time-consuming nature of
fetal aortic Doppler measurements combined with
equivocal reports reviewed above would militate
against its use in clinical care. Furthermore, variabil-