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.