What are the indications for an amniotic fluid reduction (amnio reduction)?

Indications for Amniotic Fluid Reduction (Amnio Reduction)

Amniotic fluid reduction is primarily indicated for severe polyhydramnios causing maternal symptoms such as respiratory distress or discomfort, and for twin-twin transfusion syndrome (TTTS) as a temporizing measure when laser therapy is not immediately available.

Polyhydramnios-Related Indications

Maternal Symptom Relief

• Severe maternal respiratory distress or dyspnea
• Significant maternal discomfort from abdominal distension
• Preterm contractions caused by polyhydramnios 1, 2

Amnioreduction should be considered only for severe maternal symptoms in the setting of severe polyhydramnios, not for mild cases or as a routine intervention 2. The procedure is typically performed when the maximum vertical pocket (MVP) is ≥8 cm or amniotic fluid index (AFI) is ≥24 cm 2.

Key considerations for polyhydramnios-related amnioreduction:

• Intra-amniotic pressure is significantly higher in symptomatic patients (median 15.0 mmHg) compared to asymptomatic patients (median 10.0 mmHg) 3
• The procedure aims to reduce the MVP to 5-6 cm 1
• Typically performed using an 18-20 gauge needle under ultrasound guidance 1
• May require serial procedures in cases of recurrent polyhydramnios

Twin-Twin Transfusion Syndrome (TTTS) Indications

As a Temporizing Measure

• When there are delays to timely fetal care center referral for laser therapy
• When severe maternal symptoms from polyhydramnios require immediate intervention
• For TTTS presenting beyond 26 weeks of gestation when laser therapy may not be indicated 1

In TTTS, amnioreduction involves removing fluid from the polyhydramniotic sac of the recipient twin. However, it's important to note that therapeutic amnioreduction before consultation at a fetal care center is generally not recommended due to a 15% complication rate within 48 hours 1.

Important Caveats and Considerations

Complications of Amnioreduction

• Preterm premature rupture of membranes
• Preterm labor (occurs in approximately 5.4% of cases within 48 hours) 4
• Placental abruption
• Infection
• Fetal death 1
• Chorioamnion separation or inadvertent septostomy in twin pregnancies 1

Efficacy Considerations

• Amnioreduction does not appear to prolong pregnancy in cases of moderate to severe polyhydramnios 4
• However, it may increase the likelihood of vaginal delivery and lower rates of uterine atony 4
• In TTTS, amnioreduction has been associated with 60-65% overall survival rates, which is lower than laser therapy 1

Contraindications

• Mild polyhydramnios without maternal symptoms
• Suspected intraamniotic infection
• When the procedure might delay definitive treatment (e.g., laser therapy for TTTS)

Special Situations

Bartter Syndrome

In cases of fetal Bartter syndrome with polyhydramnios, serial amniocentesis may be considered, but the risks and benefits must be carefully weighed, and a multidisciplinary team approach is recommended 1.

Measurement Technique

When evaluating for polyhydramnios, the single deepest vertical pocket measurement is preferred over amniotic fluid index, as AFI tends to overdiagnose oligohydramnios and lead to unnecessary interventions 5.

In summary, amnioreduction should be reserved for specific clinical scenarios with clear indications rather than used routinely for all cases of increased amniotic fluid. The decision should be based on severity of maternal symptoms, gestational age, and underlying etiology of the polyhydramnios.