Moise 2005.

Methods	Type of study: randomised controlled trial. Method of treatment allocation: computer‐generated randomisation with block size of 10 using a web‐based system. Stratification: none used. Sample size calculation: yes. Intention‐to‐treat analysis: yes. Losses to follow‐up: 2 women (3%) were lost to follow‐up in the septostomy arm. Funding: none mentioned.
Participants	Location: University of North Carolina. Timeframe: September 1997 to July 2002. Inclusion criteria: women with monochorionic twin gestations less than 24 weeks, polyhydramnios in one amniotic cavity (deepest vertical pool > 8 cm at < 20 weeks, > 10 cm at 20‐22 weeks and > 12 cm after 22 weeks) and oligohydramnios in the second amniotic cavity (deepest vertical pool < 2 cm). Exclusion criteria: fetal structural abnormalities, premature contractions associated with cervical change, premature rupture of membranes, suspected chorioamnionitis, or other indications for delivery. Total recruited: 73 women and 146 fetuses in both arms.
Interventions	Purposeful perforation of the inter twin membrane under ultrasound guidance with a 22‐gauge needle, from the donor sac into the recipient twin's amniotic cavity. Repeat septostomy, with or without amnioreduction was performed if re‐accumulation of the amniotic fluid in the donor twin's amniotic cavity did not occur. Cross‐over to amnioreduction arm was allowed if oligohydramnios had not resolved in the donor twin's sac or if the deepest vertical pool in the recipient twin's sac had increased by 30% over baseline value. Salvage amnioreduction at the time of septostomy was performed if maternal symptoms were present. Amnioreduction of the recipient amniotic sac using a 18‐gauge needle, connected either to wall suction or a syringe attached to extension tubing. Fluid was removed until the deepest pool was less than or equal to 6 cm or 5 L was removed. Amnioreduction was repeated if there was excessive uterine activity, maternal respiratory compromise or polyhydramnios recurred.
Outcomes	Primary outcomes: at least 1 infant surviving until hospital discharge.
Notes	Interim analysis: planned at the midway point using O'Brien‐Fleming stopping rule for discontinuing enrolment. The trial was stopped by the Data Safety Monitoring Officer after the interim analysis because of slower than projected enrolment and almost identical perinatal mortality in either arm of the trial making it unlikely that the primary end point might be achieved.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomisation with block size of 10 using a web‐based system.
Allocation concealment (selection bias)	Low risk	Computer‐generated randomisation with block size of 10 using a web‐based system.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Not possible, the main survival outcomes are not likely to have been influenced by lack of blinding.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Intention‐to‐treat analysis: yes. Losses to follow‐up: 2 women (3%) were lost to follow‐up in the septostomy arm.
Selective reporting (reporting bias)	Low risk	All expected pre‐specified outcomes reported.
Other bias	Low risk	This trial was stopped early on the basis of interim analysis. The recruitment rate to the trial was slower than predicted and it was felt that the primary end point would not be achieved. This trial quoted the O'Brien‐Fleming rule for stopping.