Amniocentesis Test: Risks, Benefits, Accuracy, and More

The removal of amniotic fluid by using a needle through the maternal gravid abdomen has been done since 1877. Initially, it was reported as a therapeutic modality to release amniotic fluid from fetuses with polyhydramnios or to help in the management of fetuses affected by rhesus isoimmunization. Subsequently, following the discovery that cultured amniotic fluid cells could be used to obtain fetal karyotype, amniocentesis was and continues to be used for genetic diagnosis. Additionally, it is used for fetal treatment in cases such as polyhydramnios.

Amniocentesis

Indications

Multiple indications for amniocentesis exist. The most common use of amniocentesis is to diagnose fetal chromosomal anomalies after other tests such as ultrasound or biophysical markers have determined a significant likelihood that the fetus will be affected with a chromosomal problem. Other diagnostic tests performed using amniocentesis are determining fetal lung maturity and evaluating alloimmunization. Amniocentesis can also be used to obtain samples to rule out chorioamnionitis in cases in which the clinical picture is unclear, as well as to deliver intra-amniotic dye in cases in which premature rupture of membranes is suspected.

Therapeutic indications for an amniocentesis may include the direct delivery of medications to the unborn fetus and to release intrauterine pressure in the presence of polyhydramnios.

Amniocentesis

Contraindications

For the most part, amniocentesis is a safe procedure for the mother. As with any procedure involving the skin, an active skin infection on the proposed needle placement site is a fetal and maternal contraindication. Contractions of the uterus are a relative contraindication. Decreased amniotic fluid or anterior placental position may hamper the success of an amniocentesis.

Technical Considerations

Best Practices
Sterility of the procedure is important because skin contaminants can enter the amniotic fluid and create a fetal infection. Before and after the procedure, fetal heart tones should be obtained to demonstrate fetal viability. The value of the procedure should always be weighed against the risks before an amniocentesis is performed.

Procedure Planning

Consent regarding testing, expectations, complications, and limitations should be clear to the mother, including the possibility of fetal puncture with the needle, preterm labor, infection, and miscarriage. Ideally, genetic amniocentesis should be performed at a gestational age early enough to give the patient the choice of termination of pregnancy legally—usually less than 20 weeks—and late enough in the pregnancy to reduce the chances of miscarriage and foot deformities. Therefore, this procedure is safest between 15 and 18 weeks gestation.Amniocentesis for other indications may be performed later in pregnancy.

Amniocentesis

Complication Prevention

Real-time ultrasound guidance is generally used for amniocentesis. By using ultrasound, the operator can direct the needle directly toward the amniotic fluid and avoid other structures, such as maternal intraperitoneal organs (bowel, bladder), fetus, or placenta. Avoiding passing the needle through the placenta is preferable because this may create bleeding or placental separation. If the clinician cannot avoid placental insertion, take care to avoid the umbilical cord insertion site, placental edges, and large placental blood vessels.

Miscarriage after amniocentesis has been traditionally reported as 1 in 200, but most recent studies report the risk to be 1 in 1,000. Amniocentesis before 15 weeks gestation, use of large needles, multiple attempts, and unrecognized chorioamnionitis postprocedure are risk factors for miscarriage. The risk of talipes equinovarus is elevated if the amniocentesis is performed prior to 15 weeks gestation.

Additionally, maternal viral infections may be transmitted to the fetus via this procedure. The rate of transmission of HIV is associated with the mother not being on antiretrovirals, and the risk of hepatitis B is associated with the maternal viral load at the time of the procedure.Therefore, counseling regarding risk-benefit analysis should occur with those patients before the procedure.

Amniocentesis

Outcomes

The goal is to obtain a “clear tap,” indicated by return of clear amniotic fluid during the procedure, without inserting the needle through viable maternal and fetal organs, avoiding preterm contractions, and avoiding a miscarriage.