What is amnioreduction?

The removal of a large volume of amniotic fluid from the gestational sac.

When is amnioreduction needed?

Amnioreduction is needed when pregnancy is complicated by polyhydramnios. Polyhydramnios is the increased amount of amniotic fluid that may be found in around 1% of pregnancies. Since amniotic pressure is elevated with polyhydramnios, these pregnancies are at high risk of both maternal and fetal complications.

What are the causes of polyhydramnios?

In many cases (around 50%), the exact cause cannot be identified.

  • Maternal diabetes mellitus, which causes fetal glucose level to increase resulting in increased urinary output (fetal urine is a major source of amniotic fluid).
  • Fetal anomalies that impair the ability of the fetus to swallow amniotic fluid (such as gastrointestinal abnormalities, facial cleft, neck masses, tracheoesophageal fistula, diaphragmatic hernias and neurological abnormalities).
  • Chromosomal abnormalities such as Down syndrome (Trisomy 21) and Edwards syndrome (Trisomy 18).
  • Intrauterine infection.
  • Twin-twin transfusion syndrome (TTTS) – affects identical twins which share a single placenta (Monochorionic twins).

What is the rationale behind amnioreduction? Why perform an amnioreduction?

The rationale behind amnioreduction is to restore normal amniotic fluid volume and pressure. The draining reduces maternal discomfort, improves the perfusion to the uterus and placenta, and prolongs pregnancy by limiting the risk of preterm labor and rupture of the membranes.

How is the procedure performed?

Amnioreduction is considered a technically simple procedure and may be performed without administration of anesthetics. A Maternal Fetal Medicine Specialist will perform the procedure.

This procedure is done under ultrasound guidance using sterile technique.  The use of ultrasound enables the doctor to observe the needle as it moves into the target location during the entire procedure. The amount of amniotic fluid drained varies, but the  fluid remaining should measure in the normal range.The amnioreduction procedure may cause some immediate abdominal discomfort or cramping that will usually resolve within a short time.

What are the risks of amnioreduction?

  • Contractions
  • Premature labor
  • Spontaneous premature rupture of membranes
  • Abruption of the placenta that may be present as vaginal bleeding
  • Chorioamnionitis (infection of the fetal membranes)


If you experience any of the following conditions, you should contact your doctor or go to the hospital.

  • Intense contractions
  • Rupture of membranes (water breaking)
  • Vaginal bleeding
  • Fever
  • Reduced fetal movements


Special Pregnancy Program

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Maternal Medicine: 416-586-4800 x 7000
Fax: 416-586-5109

Main clinic hours: Monday to Friday, 8am to 4pm

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phone: 416-586-4800 x 4523
fax numbers:
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Perinatal Mental Health

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Phone: 416-586-4800 x 8325
Fax: 416-586-8596