Controlled amnioreduction procedure
AR was done while simultaneously recording the removed amniotic volume,
the amniotic pressure and the flow velocity waveform (FVW) at the
umbilical cord. The controlled AR was performed via epidural 18G
hypodermic needle under continuous transabdominal ultrasound guidance
and local maternal anesthesia. The excess amniotic fluid was drained
into a sterile bag through a plastic tube and a 3-way stopcock attached
to the hub of the needle. The removed volume of fluid was recorded every
500 ml and followed by measurement of the amniotic pressure and FVW.
The amniotic pressure in the polyhydramniotic sac was measured by a
water manometer at the level of the needle tip. The stopcock was opened
to the atmosphere to allow for the amniotic fluid to flow from the
uterus into the manometer tube. After stabilization within a few
seconds, the pressure was acquired in cmH2O and
converted to mmHg by a factor of 0.74. Immediately after reading the
pressure, the tap was closed and the fluid re-directed into the sterile
bag. The twins FVW was measured with a Doppler ultrasound machine
(Sonoline Elegra, Siemens and GE Voluson E6) at the free loop of the
umbilical cord. At least five sequential normally shaped FVWs were
acquired and the umbilical artery systole/diastole (SD) ratio was
calculated.
In case of uterine contractions prior to the procedure, the patients
were treated by Indomethacin (PR, 100 mg). In case of repeated uterine
contractions, the amniotic pressure was recorded immediately after
complete relaxation. The procedure was terminated when the amniotic
pressure did not change after two sequential drainages of 500 mL each or
in case of maternal discomfort. The duration of the controlled AR was
about 80 minutes per procedure. The procedure was repeated only if TTTS
occurred again.