Main Findings
The controlled AR procedure resulted in a relatively high rate of twin
survival independently of the gestation week. Moreover, it is
objectively more efficient since it revealed positive short and
long-term outcomes. The pattern of the amniotic pressure versus the
removed fluid demonstrated an apparent exponential relationship with a
plateau and represented a logical reason for procedure duration and
termination.
The controlled AR procedure was applied to 11 pregnant women with twins
diagnosed with TTTS, including severe cases at Quintero stages II and
III. In this study group, the procedure was terminated based on amniotic
pressure measurements, rather than the removed fluid volume. There were
no cases of maternal infection or complications, as well as premature
delivery in the 48 hours post procedure.
The overall survival rate was 19/22 (86.4%), which is higher than
published outcomes of serial AR interventions 8, 10,
11, 13, 27, 28. It should be noted that the controlled AR procedure was
also successful in cases of severe TTTS in patients who were firstly
treated at the gestational ages of 17 to 32 weeks, while in published
reports AR was recommended only in cases of mild disease or when FLS
interventions were unsuccessful 9.
In the present study the amniotic fluid volume removed during the
session varied between 700-4500 ml (Figure 1). Presently, there is no
consensus regarding the amount removed per session. The published data
revealed a wide variety of values from 400 to 7500 mL, which are within
50% to 435% of the mean volume for any given gestational age2, 5, 6, 29, 30. It has been suggested that drainage
of a large quantity of amniotic fluid may result in unpredictable
changes in blood flow across the vessel connections 31and 1100 ml should be the weekly maximal removed amniotic fluid ensure
survival 32. The present study demonstrated that there
is no definite volume drainage that predicts the procedure efficiency.
The umbilical artery S/D ratio in uncomplicated twin pregnancy shows
close agreement with the normal range for singleton pregnancy33. It is obvious that reduction in amniotic fluid
volume decreases the pressure associated with polyhydramnios and leads
to increased flow from the placenta to the fetus 34.
In the present study, the initial umbilical artery S/D ratio was above
the 95th percentile of the normal range in 10 cases
and within it in 8 cases. The most noticeable positive effect
of the procedure on FVW was observed in the 3 cases of severe TTTS with
initial AEDF, but the post-procedure S/D ratio did not reach the normal
range for the given week of gestation. Nevertheless, this outcome is in
agreement with previous reports on higher fetal mortality in cases of
AEDF in either the donor or the recipient (i.e., patients 1, 4, 8)5, 28, 32, 35. The post-procedure S/D ratio changed to
be within the normal range in 63.8% of cases, below it in 4 cases
(11.2%) and above it in the remaining 9 cases (25%). We did not
observe a tendency in the S/D ratio changes due to the procedure. Thus,
we assume that post-procedure changes in S/D ratio are related to the
cardiovascular system slow adaptation to gradual changes, but
unpredictable.
The present results indicate that the pre-drainage amniotic pressure was
higher in comparison to the reference range (Figure 2) and are
consistent with some published data 20, 36-38. As
expected, amniotic pressures always decrease with fluid drainage and the
mean difference between pre- and post-procedure pressures was 9.1±5.4
mmHg. The pressure drop had an exponential pattern with a final plateau
and further volume removal had no effect, as reported by others20, 22, 39. While one study observed a linear
relationship between the removed amniotic volume and the pressure drop22, other studies could not find such a relationship20, 39.
Finally, we also followed for a long-term all surviving twins that their
mothers were treated with controlled AR. Analysis of the data revealed
that over 2/3 of the twins were neurologically normal, about 1/4 of them
demonstrated minor neurodevelopmental impairment and only one child
(about 5%) with a cerebral injury.