Amnioreduction 

Updated: Jan 24, 2019
Author: Jenny E Halfhill, DO; Chief Editor: Carl V Smith, MD 

Overview

Background

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.[1]

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.

Indications

A maternal goal in singleton pregnancies is improving maternal dyspnea.[2] 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.[3]

Amnioreduction reduces uterine distention and decreases risk for preterm premature rupture of membranes and preterm delivery.[4] 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.[5]

Contraindications

Contraindications for amnioreduction include the following:

  • Maternal or fetal bleeding disorders

  • Preterm labor

  • Suspected chorioamnionitis

The procedure should be discontinued if the needle punctures the fetus or the umbilical cord.

 

Periprocedural Care

Patient Education and Consent

Written consent must be obtained from the patient. A clear summary of the risks, benefits, and alternatives must be provided, and the patient must voice understanding. In particular, risks such as preterm labor (and delivery), infection (eg, chorioamnionitis), placental abruption (bleeding), and fetal death must be explained to the patient.[6] An overall risk of 1.5-3.1% is noted in the literature.[7]

Preprocedural Planning

Routine subjective comfort measures should be used. If the pregnancy is viable, resources that would allow cesarean delivery if necessary should be immediately available. This preparation should include placing the patient on nil per os (NPO) and, potentially, administering antenatal corticosteroids as indicated and appropriate according to standard guidelines.[8] Anesthesia standby may be appropriate (for supports ranging from intravenous [IV] sedation to general anesthesia).

Equipment

The procedure may be performed manually or with vacuum-assisted devices (eg, vacuum tubing and vacuum bottles). The materials necessary for amnioreduction include the following[9] :

  • Several 500-mL evacuation containers

  • Amniocentesis tray

  • Hard-walled arterial tubing with a 3-way stopcock

  • Specimen collection containers

  • Needles, typically 18 or 20 gauge

  • Syringe, 50 mL

  • Sterile cover sheet

  • Local anesthetic

  • Sterile gloves and towels

  • Fetal monitoring equipment

  • Ultrasound machine

Patient Preparation

Maternal sedation with benzodiazepines may reduce movement and improve comfort.[6] A local anesthetic (eg, lidocaine) is injected into the skin and subcutaneous tissue to reduce the pain associated with needle insertion.

Positioning should be optimized to permit prolonged maintenance of a stable surgical field. Proper positioning of the patient and the draining mechanisms will decrease complications.[6] The patient should be supine in a left lateral tilt position to reduce compression of the vena cava, and support pillows should be used to enhance maternal comfort.

 

Technique

Ultrasonography

Ultrasound-guided needle placement is the standard for amnioreduction.[10] Transplacental procedures should be avoided if possible.

A surgical site is created with appropriate skin scrubs and sterile towels. Sterile covers and sleeves should be available for the ultrasound transducer. Typically, the site chosen for amnioreduction is ventral to the fetus—that is, between the knees and the elbows. Before needle insertion, sonographic calipers may be used to calculate the approximate depth to which the needle should be advanced.

Current practice is to perform needle placement under direct ultrasonographic guidance, with the needle adjacent to the ultrasound transducer and sterile cover (see the image below). The needle is observed within the 2-dimensional image generated by the transducer as it moves into the target location.

Image of ultrasound-guided amnioreduction. The son Image of ultrasound-guided amnioreduction. The sonogram shows needle placement for amnioreduction in a case of polyhydramnios.

Amnioreduction may be useful in singleton pregnancies complicated by polyhydramnios.[11, 12] If a substantial amount of fluid is to be removed, the reduction in the size of the uterus may be sufficient to change the anatomic orientation. As a preemptive measure in these circumstances, inserting the needle in a cephalic direction may be prudent. As drainage continues, the needle will then become caudally directed and thus will be less likely to disengage from the amniotic cavity.

If the pregnancy is viable, a nonstress test may be performed at the completion of amnioreduction to document fetal well-being. Testing may continue to be performed weekly or twice weekly thereafter, including biophysical profiles as appropriate, depending on the indication for the procedure. If the amnioreduction was performed for twin-twin transfusion syndrome (TTTS), additional amnioreduction procedures may be required.

In cases of mirror syndrome associated with TTTS, amnioreduction alone or with selective feticide may result in complications such as a transient exacerbation of anemia and hemodilution which may cause severe maternal complications.[13]

In a Cochrane database meta-analysis of treatment interventions to improve maternal-fetal outcomes in TTTS, investigators found no difference between amnioreduction and endoscopic laser coagulation of anatomic vessels and between amnioreduction and septostomy in the following[14] : overall death, death of at least one infant per pregnancy, or death of both infants per pregnancy. Between amnioreduction and septostomy, there was also no difference in gestational age at birth. Over the long term, although more surviving babies were neurologically intact at age 6 years in the laser group than in the amnioreduction groups, no significant difference was seen between the surviving babies alive at 6 years who had major neurologic abnormalities who were treated with these interventions (laser or amnioreduction).[14, 15]

 

Medication

Medication Summary

The goals of pharmacotherapy are to reduce the pain associated with needle insertion and prevent complications.

Local Anesthetics, Amides

Class Summary

Local anesthetics are used for local pain relief.

Lidocaine (Xylocaine)

Lidocaine inhibits depolarization of type C sensory neurons by blocking sodium channels. It is injected into the skin and subcutaneous tissue to reduce the pain associated with needle insertion.