Overall, amnioreduction is an easy procedure. The rationale behind it is that the normalizing of fluid levels reduces maternal discomfort, improves uteroplacental perfusion (especially in the setting of presumed twin-twin transfusion syndrome [TTTS]), and prolongs pregnancy. 
Amnioreduction may be performed manually or with vacuum-assisted devices (vacuum tubing and vacuum bottles). Needles of differing gauges may be used (typically 18 or 20 gauge), and varying amounts of fluid may be removed at varying rates, depending on the clinical situation.
A maternal goal in singleton pregnancies is improving maternal dyspnea.  Overall, however, the most common application of or indication for amnioreduction is in the setting of twin-to-twin transfusion syndrome (TTTS), where it is performed to reduce fluid volume in the recipient twin and thereby increase blood flow to the donor twin by decreasing pressure inside the amniotic cavity. 
Amnioreduction reduces uterine distention and decreases risk for preterm premature rupture of membranes and preterm delivery.  Amnioreduction can also be performed to reduce fluid levels and pressure in cases in which an amniotic sac prolapses before cervical cerclage placement, with the goal of allowing the amniotic sac to retract back into the uterine cavity. 
Contraindications for amnioreduction include the following:
Maternal or fetal bleeding disorders
The procedure should be discontinued if the needle punctures the fetus or the umbilical cord.