Know All About : AMNIOCENTESIS

DEFINITION: Amniocentesis is the deliberate puncture of the amniotic fluid sac per abdomen.
INDICATIONS: ● Diagnostic          ● Therapeutic

DIAGNOSTIC:

Early months (15-20 weeks): Genetic amniocentesis antenatal diagnosis of chromosomal and genetic disorders:

(i) Sex-linked disorders,

(ii) Karyotyping,

(iii) Inborn errors of metabolism,

(iv) Neural tube defects.

• Later months:

(i) Fetal maturity.

(ii) Degree of fetal hemolysis in Rh-sensitized mother – Spectrophotometric analysis of amniotic fluid and deviation bulge of the optical density at 450 nm is obtained.

(iii) Meconium staining of liquor – an evidence of fetal distress.

THERAPEUTIC:

• First half:

[1] Induction of abortion by instillation of chemicals such as hypertonic saline, urea or prostaglandins. [2] Repealed decompression of the uterus in acute hydramnios.

• Second half:

(1) Decompression of uterus in unresponsive cases of chronic hydramnios producing distress or to stabilize the lie when it is not axial prior to induction.

(2) To give intrauterine fetal transfusion in severe hemolysis following Rh isoimmunization.

(3) Amnioinfusion : Infusion of warm normal saline into the amniotic cavity is done iransabdominally or transcervically to increase the volume of amniotic fluid.

Indications of amnioinfusion:

1. Oligohydramnios

(i) to prevent fetal lung hypoplasia,

(ii) to minimize umbilical cord compression during labor.

1. To dilute meconium-stained amniotic fluid.

 

PROCEDURE:

(1) After emptying the bladder, the patient remains in dorsal position.

(2) The abdominal wall is prepared aseptically and draped.

(3) The proposed site of puncture is infiltrated with 2 mL of 1% lignocaine.

 

A 20- or 22-gauge spinal needle with stylet in about 4″ In length is inserted into the amniotic cavity under real-time sonographic control (Figure). Injury to the placenta, umbilical cord and fetus is to be avoided. Continuous visualization of the needle under USG guidance reduces the risks of injury, bloody or dry tap and need of multiple insertions. The stilette is withdrawn and few drops of liquor are discarded. Initial 1-2 ml. of fluid is either used for AFP or is discarded as it is contaminated with maternal cells. Rest is used for fetal karyotyping. About 30 ml of fluid is collected in a test tube for diagnostic purposes. Fetal cardiac motion is to be seen after the procedure. Patient is asked to report for any uterine cramps, vaginal bleeding or leakage of liquor.

PRECAUTIONS: (i) Prior sonographic localization of placenta is desirable to prevent bloody tap and fetomaternal bleeding, (ii) Prophylactic administration of 100 mg of anti-D immunoglobulin in Rh-negative nonimmunized mother. Hazards are reduced significantly when it is done “under direct ultrasound control” compared to the blind procedure.

HAZARDS:

(A) Maternal complications are:

(1) Infection.

(2) Hemorrhage (placental or uterine Injury).

(3) Premature rupture of the membranes anil premature labor

(4) Maternal isoimmunization in  Rh-negative cases.

(B) Fetal hazards are:

(1) Fetal loss (1 In 400 procedures).

(2) Trauma.

(3) Fetomatenal hemorrhage.

(4) Oligohydramnios due to leakage of amniotic fluid and that may lead lo:

(i) Fetal lung hypoplasia,

(ii) Respiratory distress.

(iii) Talipes,

(iv) Amnionitis (rare).

Amniocentesis should be avoided for HIV-positive women and noninvasive tests (NT, MSAFP, anatomic USG) are preferred. However in women with HBV, HCV may be done with counseling.

Early amniocentesis (11 – 14 weeks) not to be done for genetic indications as the cell culture failure rate is high less fluid is withdrawn. Rates of complications are high.