o_1977r8vv9vk1ts2ms0kd8pksa.pdf

324 E.P. Gaziano, U. F. Harkness
procedure compared with only one such measurement
after amnioreduction.
Improvement in TTS has been reported after therapeutic
amniocentesis [89]. At 22 weeks after several
amniocenteses, the smaller twin developed signs of
congestive heart failure and absent diastolic flow.
Another amniocentesis was performed after which
the hydrops resolved and the diastolic flow in the
umbilical artery improved.
Doppler values in the MCA have been monitored
in women undergoing therapeutic amnioreduction
[90]. Pulsatility index of the MCA fell after amniocentesis
in all fetuses, although there was no consistent
trend in response of the umbilical artery PI. Fetal
stress is expected to cause a reduction in PI of the
MCA as a brain-sparing response. An acute fall in
amniotic fluid pressure likely creates an effective hypovolemia
to which the fetus responds with dilation
of resistance vessels in the brain reflected as a decrease
in cerebral artery PI. Close fetal monitoring is
recommended to avoid acute changes in pressure during
amnioreduction [90].
Long-term outcomes were reported in 33 women
with TTS who underwent amnioreduction [91]. None
of the infants (16 sets of twins) developed major neurological
handicap if both twins met the following conditions:
were delivered after 27 weeks; were without congenital
malformations; and both twins survived the
neonatal period. Eight sets of twins had at least one
twin with absent end-diastolic flow in the umbilical artery
before the first amnioreduction; all except one of
these twins either died in utero or after birth.
Survival was reported [92] for 13 of 14 co-twins
(93%) after selective reduction using bipolar diathermy
of either the donor or recipient twin in pregnancies
complicated by stage III/VI TTS as defined by
the staging system of Quintero et al. [86]. Three donors
and four recipients had absent or reversed enddiastolic
flow in the umbilical artery prior to the procedure.
In all those with absent end-diastolic flow before
the procedure, positive end-diastolic flow was restored,
in the majority of cases, within 24 h following
selective reduction. None of the co-twins later developed
absent end-diastolic flow.
Laser ablation of the connecting vessels in TTS is
an appealing option in the management of the worse
forms of TTS since it is the sole treatment modality
which corrects one of the underlying pathophysiologic
defects and has been demonstrated to be effective
[6]. Randomized clinical trials are now underway to
assess laser ablation. All treatment options are subject
to failure since many cases of TTS are in pregnancies
in which there is significant asymmetrical distribution
of the placental mass (see placental symmetry)
as well as the presence of abnormal cord insertions
in the affected twins.
Summary
Given the limited data from multiple relatively small
studies and the causes of the fetal Doppler findings
in TTS, the following list attempts to summarize current
observations:
1. Twin transfusion syndrome is a complex pathophysiologic
event for which there is no predictable
pattern of vascular anastomosis and no uniform
pattern of Doppler abnormality.
2. Differences in umbilical artery Doppler parameters
are relatively common in twin pairs with TTS.
3. Abnormal umbilical artery velocimetry may be
seen in either the donor or the recipient fetus, but
it is more common in the growth-restricted donor
fetus with oligohydramnios.
4. Abnormal umbilical venous flow may be seen in
the circulation of the hydropic recipient fetus.
5. Abnormal velocimetry in TTS, particularly low
diastolic velocities in the umbilical artery, is associated
with a poor outcome and justifies the use of
intensive surveillance.
6. Clinical criteria for TTS are difficult to define because
of the individual and varying complexity of
the vascular arrangements.
7. There may be a role for Doppler velocimetry in
TTS staging, to determine the most appropriate
treatment options, and to monitor disease progression.
Doppler Velocimetry and Outcome
in Twin Pregnancies
Third-Trimester Doppler Studies
Velocimetry of the umbilical artery appears superior
to that in the fetal ascending aorta, pulmonary artery,
or internal carotid artery [93]. Singleton SGA infants
with abnormal umbilical artery velocimetry have increased
admission rates and prolonged courses in the
neonatal intensive care unit (NICU) [51]. Fetuses with
growth restriction and normal Doppler values have
less morbidity than growth-restricted fetuses with abnormal
values [94]. A variety of adverse events, including
fetal distress, premature delivery, the presence
of SGA, and low birth weight, are more common
in Doppler-abnormal than in Doppler-normal fetuses
[95].
The outcome of fetal growth restriction can be
classified according to umbilical artery Doppler
values [96], and the increased neonatal morbidity in
SGA infants with abnormal antenatal umbilical artery
Doppler findings has been repeatedly supported [97].
Abnormal resistance in the descending fetal aorta is
associated with increased perinatal risk for death,
necrotizing enterocolitis, and hemorrhage, whereas
75% of SGA infants with normal values had uncom-