Chapter 227 Amniocentesis
DESCRIPTION
Amniocentesis is the sampling of fluid from around the growing fetus for prenatal biochemical or genetic diagnosis. Rarely, amniocentesis may be used to reduce the amount of amniotic fluid present in cases of polyhydramnios.
INDICATIONS
The assessment of fetal genetics or metabolic disorders, lung maturity, fetal infection, or isoimmunization status. Therapeutic amniocentesis may be performed for the reduction of fluid volume or the instillation of agents for fetal therapy or other purposes such as fetal imaging or the diagnosis of rupture of the fetal membranes. Amniocentesis is also a necessary step in other diagnostic and therapeutic procedures such as cordocentesis or fetal transfusion.
CONTRAINDICATIONS
Active skin infections near the site of needle placement. Relative; maternal fever of unknown origin, known or suspected allergies to materials used (e.g., latex, skin preparation materials, local anesthetics). Amniocentesis may be technically difficult to accomplish in patients with multiple gestations.
REQUIRED EQUIPMENT
TECHNIQUE
The indications, contraindications, risks, benefits, and complications should be reviewed and discussed with the patient, and informed consent should be obtained. The patient should be placed in the supine position with the head elevated 20 to 30 degrees. If the pregnancy is advanced, the patient may empty her bladder and be placed in a slightly left decubitus position. Ultrasonography is used to assess fetal well-being, fetal lie, and placental position.
A suitable pocket of amniotic fluid should be identified by use of ultrasound. Ideally, this pocket should be located away from the fetal face and placenta, but it should be accessible with a standard spinal needle. Areas around the fetal extremities are often best. The location of this pocket relative to the skin surface should be noted as a guide to needle insertion.
The skin of the abdominal wall over the chosen pocket of amniotic fluid should be disinfected with a suitable skin preparation solution and technique of the examiner’s choice. If a local anesthetic is to be used, it is established at this juncture using sterile technique: A small skin weal of local anesthetic is placed, and the proposed needle track is infiltrated with a total of less than 4 to 5 mL of anesthetic agent.
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