Continuing Education ActivityAmniocentesis is the aspiration of amniotic fluid from the amniotic cavity and is the most common invasive fetal testing procedure. Amniocentesis is an invasive technique. It is usually performed to diagnose or exclude fetal aneuploidy or other fetal genetic, biochemical or infectious risks. Prenatal diagnosis enables the diagnosis of a broad spectrum of chromosomal abnormalities, gene disorders, X-linked conditions, neural tube defects, and infections to be made before the birth of the fetus. The indications grow with progress in these fields. This activity outlines the procedure, reviews its complication rates, describes the complexity of obtaining truly informed consent, and examines the role of the healthcare team in improving care for high-risk patients who undergo this invasive procedure. Show
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Access free multiple choice questions on this topic. IntroductionPrenatal diagnosis enables the diagnosis of a broad spectrum of chromosomal abnormalities, gene disorders, X-linked conditions, neural tube defects, and infections to be made before the birth of the fetus. The various invasive prenatal diagnostic tests are amniocentesis, chorionic villus sampling, and fetal blood sampling or cordocentesis. Amniocentesis Amniocentesis is an invasive technique. This technique removes amniotic fluid from the uterine cavity using a needle. This procedure is performed transabdominally and under ultrasound guidance by a trained obstetrician. It was first performed for the diagnosis of genetic diseases (sex determination) of the fetus by Fuchs and Riis in 1956.[1] It is performed for diagnostic and therapeutic purposes, including for diagnostic evaluation in the form of chromosomal, biochemical, histopathological, and microbial assessments. When performed as a therapeutic procedure, it is done to reduce the volume of amniotic fluid in patients with polyhydramnios.[2][3][4] The amniotic fluid obtained consists of fetal exfoliated cells, transudates, fetal urine, and lung secretions. Amniocentesis can be performed from 15 weeks of gestation to delivery, with an attributable risk of loss in experienced hands of 0.13% in singletons. Earlier the attributable risk is greater than chorion villus sampling (CVS), which provides similar data from 11 to 15 weeks. There is an increased risk of amnionic fluid leakage of 1 to 2%, most of which corresponds to decreased activity in days and fetal demise, which is usually much rarer than the risk of demise attributable to the indication for the procedure, except in low-risk women with no maternal risks indicating the procedure, and talipes equinovarus, presumably from oligohydramnios.[5] Counseling of the couple is necessary regarding the procedure's indications, risks, benefits, and limitations.[6] This can be complex, as the individual circumstances leading to risk, including maternal age, parental family history, maternal serum screening, sonographic signs of chromosomal and other problems, and population history, can vary significantly. The benefit of possible pregnancy termination also varies depending on the patient's education, religious and ethical preferences, and, at present, state law. Chorionic Villus Sampling It is a prenatal invasive procedure and is done under ultrasound guidance. This procedure uses ultrasonography to guide the catheter or needle into the chorion frondosum. It is done abdominally and is followed by tissue aspiration (chorionic villi) for genetic or chromosomal analysis with a syringe containing tissue culture media. It is done in the first trimester for prenatal diagnosis between 10 to 14 weeks. Depending on the position of the uterus and bladder, the patient's gestational age, and placental localization, it can be performed transabdominally or transcervically. The safer and earlier termination of pregnancy is possible as karyotype results are available within 7 to 10 days, although placental mosaicism is a risk for a false diagnosis or reassurance. It is indicated in chromosomal and genetic disorders. The samples collected are sent for DNA analysis. It is not performed in vaginal bleeding, in cases of cervical abnormalities, and severe infections. The major complications involved in this procedure are limb reduction defects from earlier procedures, chromosomal abnormalities present in the extraembryonic tissue, which are not found in the fetal tissue, intrauterine infections, membrane rupture, and fetal loss. The attributable risk in trained hands is similar to amniocentesis. Both procedures assume direct ultrasound guidance for a safe procedure. Fetal Blood Sampling or Cordocentesis It is the technique in which, under ultrasound guidance, fetal blood sampling is performed through the maternal abdomen. It is usually performed after 18 weeks after visualization of cord insertion. As the lumen of the cord at earlier weeks of gestation is narrow, it is considered safer to perform at 20 to 28 weeks of gestation. The blood sample is sent to the laboratory for hematological, immunological, and biochemical analysis. The results are obtained within 24 to 72 hours. There is an increased risk of fetal loss, which is comparatively higher (1 to 3% attributable risk) compared with other invasive procedures. The benefits include conversion to fetal transfusion, which can be life-saving. This is commonly indicated in maternal blood group sensitization from a transfusion or prior or current pregnancy sensitization to fetal cells from delivery or miscarriage of fetomaternal hemorrhage, suspected in the case of aplastic anemia from fetal Parvovirus B19 infection with the maternal acquisition of "Slapped face fever" - more common in teachers, parents, and childcare workers.[7] Anatomy and PhysiologyAmniotic fluid is a transparent fluid with a light yellowish color. It is present in the amniotic sac. It creates a space for the fetus to grow and survive. It helps permit fetal movements, which are necessary for the effective musculoskeletal development of the fetus. It helps in fetal swallowing and fetal breathing. Development On the 8th day, the trophoblast changes. Bilaminar germ disc formation occurs after the differentiation of embryoblast. On the dorsal aspect of the bilaminar germ disc, there is the presence of tall columnar cells. They are ectodermal in origin. On the ventral aspect of the bilaminar germ disc, flattened polyhedral endodermal cells are present. Connecting stalk forms the umbilical cord later; it connects the bilaminar germ disc with the trophoblast. There is the appearance of 2 cavities on either side of the germ disc:
Physiology of Amniotic Fluid Maternal and fetal compartments are essential in forming amniotic fluid in the first trimester of pregnancy. Fetal skin is non-keratinized in earlier weeks, allowing free transfer of water and other small molecules and solutes through the amnion and chorionic.[8] Amniotic fluid is similar to maternal and fetal extracellular fluid and functions as a nonsterile aqueous electrolyte solution. During the second trimester of pregnancy, the diffusion process ceases as keratinization of fetal skin occurs, making the fetal skin impervious to water and other solutes. On transvaginal ultrasonography, urine is observed at nine weeks in the fetal bladder, and on transabdominal sonography, urine is seen at 11 weeks of gestation.[9][10] During this period, the major component of the amniotic fluid is fetal urine. It is hypotonic (80 to 140 mOsm/liter), and as the fetal kidneys mature, they contain increased concentrations of urea, uric acid, and creatinine. At term, a fetus produces 500 to 700 ml of urine per day.[11][12][13] The average amniotic fluid volume at 12 weeks of gestation is 60 mo.[10] By 16 weeks, the mean volume is 175 ml.[14] From 20 weeks on, amniotic fluid volume varies. Amniotic fluid volume increases steadily throughout pregnancy to a maximum of 400 to 1200 ml at 34 to 38 weeks.[14][15][16] Near term, the net increase of amniotic fluid is only 5 to 10 ml/day in the third trimester. After 38 weeks, fluid volume declines by approximately 125 ml/week to an average volume of 800 ml at 40 weeks.[14][15][16] IndicationsAmniocentesis is a commonly performed procedure for several reasons. It is performed for:
Diagnostic Indications Chromosomal Analysis Karyotyping and DNA analysis (to diagnose sex-linked disorders, inborn errors of metabolism, and neural tube defects).
Genetic Testing Analysis for Alpha-fetoprotein Level and Acetylcholinesterase Assessment of Severity of Rh Isoimmunisation Assessment of Bilirubin Levels in Amniotic Fluid and Grade of the Severity of Alloimmunization Recently non-invasive tests, including the middle cerebral artery Doppler, have gained more importance. It is usually done in the third trimester of pregnancy. Diagnosis of Fetal Infections It can assist in diagnosing TORCH infections.[17] These include:
Fetal Lung Maturation (L/S ratio) Performed in the third trimester of pregnancy. Diagnosis of Chorioamnionitis Diagnosis of Inherited Bleeding Disorders Such as moderate to severe hemophilia A and B and type 3 von Willebrand disease (VWD) in the third trimester of pregnancy. These disorders have increased fetal risk of intracranial bleeding during delivery.[18] Therapeutic Indications
ContraindicationsThere are no absolute contraindications for amniocentesis. Relative contraindications for amniocentesis are:
EquipmentThe procedure is done under continuous ultrasound guidance. The following equipment is required:
Personnel
Preparation
TechniqueAmniocentesis is done as an outpatient procedure. After proper genetic counseling and informed written consent, a detailed ultrasound is performed to assess the gestational age, placental localization, gross congenital anomalies, maximum vertical pocket (MVP) of amniotic fluid, fetal position, fetal movements, fetal cardiac activity, and amniotic fluid volume. Skin is prepared with povidone-iodine, and sterile ultrasonography gel is applied. After confirming the prerequisites and once the preparation is complete, amniocentesis is performed using the aseptic technique. A 20- to 22-gauge spinal needle is used to enter the amniotic cavity under continuous ultrasound guidance. The entire procedure should be performed in real-time sonographic monitoring with continuous, direct visualization of the spinal needle. The needle is directed to the clear region in the deepest amniotic fluid pocket. Needle insertion in the upper third of the uterus is less painful.[25] The needle, in ideal conditions, is inserted perpendicular to the skin. The transducer is placed in a way that the ultrasound beam is directed at a 15 to 20-degree angle from the planned track of the needle. Figure 1 shows the ultrasound picture of the inserted needle during the amniocentesis procedure. It must be ensured that fetal parts, umbilical cord, or placenta are not present in the region of needle insertion. Transplacental puncture is usually not the preferred point of entry.[26] Transplacental entry is strictly avoided in cases of alloimmunization or infections to the mother, like human immunodeficiency virus (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV).[27][28] A firm entry into the amniotic cavity is recommended to prevent the tenting of the amniotic membrane.[29] Once entry into the cavity is confirmed, amniotic fluid is slowly aspirated. The initial 1 ml to 2 ml of amniotic fluid is discarded because it has the highest chance of maternal cell contamination.[29] Approximately 18 ml to 20 ml of amniotic fluid is required for karyotype testing, and 2 ml to 5 ml is required to test for enzyme deficiency testing. The needle is removed after adequate amniotic fluid has been obtained. Fetal wellbeing is confirmed by assessing fetal cardiac activity regularity and fetal movements. This should be witnessed by the patient on ultrasound post-procedure and documented. Amniocentesis in twin pregnancies requires the determination of chorionicity and amnionicity. In dichorionic twins, there are two methods: single-needle technique and two-needle insertion technique. In the single needle technique, after collecting amniotic fluid from one sac, the syringe with the amniotic fluid of the first fetus is removed, and the needle pierces through the septum separating the two amniotic sacs to collect the amniotic fluid from the amniotic sac of the second fetus. This technique has a risk of contamination from the first sac. In the two-needle insertion technique, after collecting amniotic fluid from one sac, a small amount of blue-colored indigo carmine dye is injected into the sac of the first twin. Then the needle has pierced the skin and is placed into the sac of the second twin, and fluid is withdrawn. Repeat sampling of blue amniotic fluid allows the operator to know if the amniotic fluid of the first fetus is sampled twice.[30][31] The patient should be observed after amniocentesis for a short time. She should be instructed to report if there is any vaginal fluid leaking, vaginal bleeding, severe uterine pain, or fever. Routine activities can be resumed after the procedure, but the patient should avoid strenuous exercise. Amniocentesis done without ultrasound guidance has 5 to 10 percent failure rates, where no amniotic fluid is aspirated.[32] Sometimes when amniocentesis is attempted using a suprapubic needle insertion, there is doubt of the fluid aspirated, be it maternal urine or amniotic fluid. The presence of urea and potassium in maternal urine and crystalline arborization pattern of dried amniotic fluid in slide observed under magnification confirms the fluid origin.[33][34] ComplicationsBoth maternal and fetal complications can occur with amniocentesis. Maternal Complications
Fetal Complications
Clinical SignificanceAmniocentesis procedure is relatively safe, with fewer complications among experienced hands. The location of the placenta is an important factor in amniocentesis. While performing the procedure, one should try to avoid penetration of the placenta. The anterior and fundal placenta is associated with more complications, including multiple pricks and blood-stained liquor; however, it is not associated with increased fetal loss rates.[37] Passing the needle through the placenta is slightly associated with increased preterm birth rates.[38] After the amniocentesis procedure, the sample of amniotic fluid is taken to a laboratory for testing. Results usually take ten days to three weeks depending upon the laboratory. In the laboratory, genetic and chemical tests are done. For genetic tests, specific chromosomes and genes undergo analysis. A. For chromosomal and genetic testing, the amniotic fluid is sent for a conventional cell culture report, which is obtained in 14 days. Rapid chromosomal preparations are available that give results in 1 to 2 days, including fluorescent in-situ hybridization (FISH) and quantitative fluorescence polymerase chain reaction (QF-PCR). Commonly Performed Tests 1. Rapid test: A rapid test looks for abnormalities on specific chromosomes. This test is almost 100% accurate. A rapid test can identify some chromosomal conditions that cause physical and mental abnormalities. These are:
2. Full karyotype: The cells in the sample of amniotic fluid are grown for up to 10 days in a laboratory before being examined under a microscope to check for:
Results from a full karyotype will usually be available in two or three weeks. Amniocentesis in the third trimester has higher cell culture failure rates. Uncommon Tests
B. Amniotic fluid is analyzed for the presence of proteins, minerals, and other compounds. Amniocentesis results will either be positive or negative. Acetylcholinesterase (AChE), in conjunction with elevated alpha-fetoprotein (AFP) in amniotic fluid, is considered diagnostic for open neural tube defects.[43] C. Turbid amniotic fluid should be sent for microbiological culture to detect the presence of any organism. Antibiotic coverage should be given to the patient. Occasionally, brown or green amniotic fluid is aspirated during amniocentesis due to intra- amniotic hemorrhage before the amniocentesis procedure due to the breakdown of blood products.[44] Various studies have shown higher fetal loss rates with the aspiration of such discolored fluid.[45][5] For most chromosomal conditions, there is no cure, so the couple needs to be appropriately counseled regarding the continuation of pregnancy. Enhancing Healthcare Team OutcomesThe decision to perform amniocentesis and to convey the results to the couple requires communication between geneticists and fetal medicine experts operating as an interdisciplinary and interprofessional team. Geneticists must counsel the patient to know the possibility of the fetus being affected by a genetic disease. The genetic counselors should educate themselves and verify the availability of the required laboratory testing facilities prior to suggesting a prenatal diagnostic test to the patient. The operator should be aware of the type of samples required to be collected, the type of procedure to be performed, knowledge of the sample collection instrument, sample storage and handling instructions, and prescribed ways to transport the samples. Following the counseling session, the patient is referred for the procedure. While performing the procedure, coordination amongst the team is required. Once the needle is inside the amniotic cavity, the assistant should carefully and promptly withdraw the amniotic fluid so that the procedure is performed in the minimal time possible and with minimal risk of needle displacement. Following the test, the implications of the report should be conveyed to the patient and her family by the geneticists. Consultation with the pediatrician and disability center counselors can be arranged for the patient if required. Meetings with the diagnosed disability social support group and families dealing with a similar disability in a family member help the patient make a proper decision. Review QuestionsFigureUltrasound picture showing needle insertion during real time sonography guided amniocentesis. Contributed by Zalak Karena, MS References1.Eddleman KA, Malone FD, Sullivan L, Dukes K, Berkowitz RL, Kharbutli Y, Porter TF, Luthy DA, Comstock CH, Saade GR, Klugman S, Dugoff L, Craigo SD, Timor-Tritsch IE, Carr SR, Wolfe HM, D'Alton ME. 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Semin Perinatol. 2012 Jun;36(3):169-74. [PubMed: 22713497] 31.Weisz B, Rodeck CH. Invasive diagnostic procedures in twin pregnancies. Prenat Diagn. 2005 Sep;25(9):751-8. [PubMed: 16170858] 32.Simpson NE, Dallaire L, Miller JR, Siminovich L, Hamerton JL, Miller J, McKeen C. Prenatal diagnosis of genetic disease in Canada: report of a collaborative study. Can Med Assoc J. 1976 Oct 23;115(8):739-48. [PMC free article: PMC1878820] [PubMed: 61796] 33.Guibaud S, Bonnet M, Dury A, Thoulon JM, Dumont M. Letter: Amniotic fluid or maternal urine? Lancet. 1976 Apr 03;1(7962):746. [PubMed: 56559] 34.Elias S, Martin AO, Patel VA, Gerbie A, Simpson JL. Analysis for amniotic fluid crystallization in second-trimester amniocentesis. Am J Obstet Gynecol. 1979 Feb 15;133(4):401-4. [PubMed: 434004] 35.Harris A, Monga M, Wicklund CA, Robbins-Furman PJ, Strecker MN, Doyle NM, Mastrobattista J. Clinical correlates of pain with amniocentesis. Am J Obstet Gynecol. 2004 Aug;191(2):542-5. 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[PubMed: 27101119] 40.Eisenberg B, Wapner RJ. Clinical proceduress in prenatal diagnosis. Best Pract Res Clin Obstet Gynaecol. 2002 Oct;16(5):611-27. [PubMed: 12475543] 41.South ST, Chen Z, Brothman AR. Genomic medicine in prenatal diagnosis. Clin Obstet Gynecol. 2008 Mar;51(1):62-73. [PubMed: 18303500] 42.McConkie-Rosell A, Finucane B, Cronister A, Abrams L, Bennett RL, Pettersen BJ. Genetic counseling for fragile x syndrome: updated recommendations of the national society of genetic counselors. J Genet Couns. 2005 Aug;14(4):249-70. [PubMed: 16047089] 43.Cheschier N., ACOG Committee on Practice Bulletins-Obstetrics. ACOG practice bulletin. Neural tube defects. Number 44, July 2003. (Replaces committee opinion number 252, March 2001). Int J Gynaecol Obstet. 2003 Oct;83(1):123-33. [PubMed: 14626221] 44.Hankins GD, Rowe J, Quirk JG, Trubey R, Strickland DM. Significance of brown and/or green amniotic fluid at the time of second trimester genetic amniocentesis. Obstet Gynecol. 1984 Sep;64(3):353-8. [PubMed: 6205335] 45.Cruikshank DP, Varner MW, Cruikshank JE, Grant SS, Donnelly E. Midtrimester amniocentesis. An analysis of 923 cases with neonatal follow-up. Am J Obstet Gynecol. 1983 May 15;146(2):204-11. [PubMed: 6189400] Why can't you have an amniocentesis before 14 weeks?There are also some other risks, such as infection or needing to have the procedure again because it was not possible to accurately test the first sample. The risk of amniocentesis causing complications is higher if it's carried out before the 15th week of pregnancy, which is why the test is only done after this point.
What procedure is done between the 15th and 18th weeks of pregnancy in which amniotic fluid is withdrawn?An alternative to CVS is a test called amniocentesis. This is where a small sample of amniotic fluid, the fluid that surrounds the baby in the womb, is removed for testing. It's usually carried out between the 15th and 18th week of pregnancy, although it can be performed later than this if necessary.
Why can amniocentesis be done earlier?Having amniocentesis early (before week 15 of the pregnancy) has been associated with an increased risk of the unborn baby developing club foot. Club foot, also known as talipes, is a congenital (present at birth) deformity of the ankle and foot.
What is the most common reason to have an amniocentesis?Besides identifying Down syndrome, amniocentesis can be used to diagnose other genetic conditions, such as cystic fibrosis. Having unusual ultrasound findings. A health care provider might recommend amniocentesis to diagnose or rule out genetic conditions associated with unusual ultrasound findings.
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