2006-09-12-09 Amniocentesis: indications, technique and complications © Font www.thefetus.net/

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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)

Indications

Diagnostic	Therapeutic
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

Technique

• 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:

• Povidine iodine solution
• Cotton balls, towel clamp and cup
• Two 20-cc syringe
• Spinal needle (22 g x 9 cm)
• Four sterile blue towels
• Gauze sponges

Amniocentesis tray

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.

Complications

• 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.

Important Evidence

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.

 

 

References

1. Prenatal Diagnosis and Reproductive Genetics. Kuller J, Chescheir N, Cefalo R. Chapter 18. Mosby edit. 1996

2. Alfirevic Z, Sundberg K, Brigham S. Amniocentesis and chorionic villus sampling for prenatal diagnosis (Cochrane Review). In: The Cochrane Library, Issue 2, 2005.]

3. Alfirevic Z, Neilson J. Editorial. Antenatal screening for Down"s syndrome BMJ  2004;329:811-812

4. Nolan GH, Schmickel RD, Chantaratherakitti P, Knickerbocker C, Hamman J, Louwsma G. The effect of ultrasonography on midtrimester genetic amniocentesis complications. American Journal of Obstetrics and Gynecology 1981;140:531-4.

5. Sundberg K, Bang J, Smidt Jensen S, Brocks V, Lundsteen C, Parner J et al. Randomised study of risk of fetal loss related to early amniocentesis versus chorionic villus sampling. Lancet 1997;350(9079):697-703.

6. American College of Obstetricians and Gynecologists (ACOG). Prenatal diagnosis of fetal chromosomal abnormalities. Washington (DC): American College of Obstetricians and Gynecologists (ACOG); 2001 May. 12 p. (ACOG practice bulletin; no. 27).

7. Tabor A, Madsen M, Obel EB, Philip J, Bang J, Norgaard-pedersen B.Randomized controlled trial of genetic amniocentesis in 4606 low risk women. Lancet 1986; 1:1287-93.

8. Harris RA, Washington E, Nease RF Jr, et al. Cost utility of prenatal diagnosis and the risk-based threshold. Lancet. 2004;363:276-282.

9. Jeanty P, Rodesch F, Romero R, et al. How to improve your amniocentesis technique. Am J Obstet Gynecol. 1983;146:593-596.

10. Eddleman K, Berkowitz R, Kharbutli Y, Malone F, Flint Porter T, et al. Pregnancy loss rates after midtrimester aminocentesis the FASTER trial. Am J Obstet Gynecol 2003;189(6):S111.

11. Centers for Disease Control and Prevention. Chorionic villus sampling and amniocentesis: recommendations for prenatal counseling. Morbidity and Mortality Weekly Report, volume 44, number RR-9, July 21, 1995.

12. Amended Canadian Guideline for Prenatal Diagnosis(2005) Change to 2005 — techniques for prenatal diagnosis. J obstet gynaecol Can 2005;25(11):1048-1054

13. Royal College of Obstetricians and gynaecologists. Amniocentesis and Chorionic villous sampling. Guideline No. 8 (revised). London: RCOG Press; 2005.

14. Williamson RA, Varner MW, Grant SS. Reduction in amniocentesis risks using a real-time needle guide procedure. Obstet Gynecol 1985;65:751—5.

15. Giorlandino C, Mobili L, Bilancioni E, D'Alessio P, Carcioppolo O, Gentili P, et al. Transplacental amniocentesis: is it really a high-risk procedure? Prenat Diagn 1994;14:803—6.

16. Marthin T, Liedgren S, Hammar M. Transplacental needle passage and other risk-factors associated with second trimester amniocentesis. Acta Obstet Gynecol Scand 1997;76:728—32.

17. Hess LW, Anderson RL, Golbus MS: significance of opaque discolored amniotic fluid at a second trimester amniocentesis, Obstet Gynecol 67:44,1986