2006-09-12-09 Amniocentesis: indications, technique and complications © Font www.thefetus.net/
Amniocentesis: indications, technique and complications
Guillermo Font, MD, Fernando Mahmoud, MD, Mariana Solari MD, Luis Garcia MD.
Mercy Hospital, Chicago, Illinois, USA
Introduction: Amniocentesis is a frequently performed invasive procedure during pregnancy, that should be performed under ultrasound guidance, which requires specialized training and ongoing experience. The aim of this article is to review indications, technique and complications associated with amniocentesis.
Definition: Amniocentesis is a diagnostic and/or therapeutic procedure performed by inserting a hollow needle under ultrasound guidance through the abdominal wall into the amniotic cavity and withdrawing amniotic fluid.(1)
| Genetic screening || Treatment of polydramnios|
| Karyotype analysis (cytogenetic accuracy greater than 99%) || |
| Fetal lung maturity evaluation || |
|Diagnosis of premature rupture of membranes and sub clinical chorioamnionitis || |
| Rh isoimmunization || |
Genetic amniocentesis is ideally performed between 15 to 20 weeks gestation.
Fetal loss rate is approximately 0.5% and complications occur infrequently.
Performing amniocentesis at less than 14 weeks increases the risks for pregnancy loss 2.7%, talipes 1.4% and membrane rupture.
Amniocentesis for other reasons is performed when medically indicated.
Materials needed for amniocentesis:
Ultrasound is performed prior to amniocentesis to confirm fetal viability, gestational age, number of fetuses, placental location, amniotic fluid volume, fetal anatomical survey, uterine cavity abnormalities or presence of fibroids. Needle insertion site is identified by ultrasound, the skin is cleaned with an antiseptic, prepped and draped. Ultrasounds prove should be covered with a sterile glove or bag. The procedure is usually performed with a 20- to 22-gauge spinal needle.
A 20 cc syringe is used to aspirate the amniotic fluid following removal of the needle stylet. The first 2 cc should be discharged and then using another syringe we remove 15 to 20 cc of amniotic fluid. Removal of the amniotic fluid generally takes less than 1 minute. Amniocentesis related risk are decreased by avoiding multiple needle insertions, and transplacental passage.
- Fetal loss or miscarriage
- Amniotic fluid leakage
- Vaginal bleeding
- Uterine cramping or contractions
- Uterine infections
- Rh sensitization
- Fetal injury
- Transmission of mother infections as Hepatitis B, C, HIV
The risk of fetal loss or miscarriage is between 0.5%-1 %, this means that 1 pregnant women in 200 - 100 amniocentesis is going to have a fetal loss. Fetal loss due to amniocentesis seems to occur within the first 2 to 3 weeks following the procedure.(1,2,6)
The risk of amniotic fluid leakage is around 1-2%.
The risk of infection after an amniocentesis is as low as 0.1%.
The risk of Rh sensitization is very low since the use of antibody anti-D ( rhogan) after the procedure in all patients at risk.
Amniocentesis should be performed after 14 weeks, in a large prospective randomized study has reported a greater loss of pregnancy when the procedure was perform early (7.6% vs. 5.9%), it also shows a 10 fold increase of incidence of fetal talipes. So commonly amniocentesis is performed between 15-18 weeks of gestation when the amount of fluid is adequate ( Approx. 150 ml). Prior to the procedure an ultrasound scan should be performed to determine the number of fetuses, viability, and document anatomy, confirm gestational age and locate placenta and umbilical cord. Amniocentesis is associated with higher rates of successful taps and lower rates of bloody taps (reduced it from 2.4% to 0.8%) when performed under direct ultrasound control with continuous needle tip visualization. Best practice is that ultrasound scanning during the procedure should be performed by the person inserting the needle. The needle diameter should not be wider than 20- gauge, the smallest the less fluid flow from the puncture site. The use of local anesthetic is no longer recommended after a Randomized Trial which shows no difference in the pain scores between women undergoing amniocentesis with and without it. Transplacental passage of the needle should be avoided; however there is enough evidence to confirm that penetration may not be associated with increased complications, but the needle should be inserted through the thinnest portion, and try to avoid the umbilical cord insertion.
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