User:Wikichi2/Amniocentesis

Medical uses

Genetic diagnosis

Amniocentesis is offered to pregnant individuals whose fetus has an increased risk of chromosomal, genetic, and other fetal problems such as :

• Down syndrome, also known as Trisomy 21
• Trisomy 13, also known as Patau syndrome
• Trisomy 18, also known as Edwards syndrome
• Sex chromosome aneuploidies, also known as sex chromosome anomalies
• Fragile X
• Neural tube defects (anencephaly and spina bifida) by alpha-fetoprotein levels.
• Tay Sachs disease
• Rare, inherited metabolic disorders

Lung development

Amniocentesis can be used to test fetal lung development. Problems with lung development can increase the risk of infant respiratory distress syndrome. Fetal lung development can be tested by sampling the amount of surfactant in the amniotic fluid in pregnancies greater than 30 weeks. Several tests are available, including the lecithin-sphingomyelin ratio ("L/S ratio"), the presence of phosphatidylglycerol (PG), or the surfactant/albumin (S/A) ratio.

• For the L/S ratio, if the result is less than 2:1, the fetal lungs may be surfactant deficient.
• The presence of PG usually indicates fetal lung maturity.
• For the S/A ratio, the result is given as mg of surfactant per g of protein. An S/A ratio <35 indicates immature lungs, 35-55 is indeterminate, and >55 indicates mature surfactant production.

Infection

Amniocentesis can detect infections via decreased glucose level, a Gram stain showing bacteria, or abnormal differential count of white blood cells.

Rh Incompatibility

Amniocentesis can be used to diagnose Rh incompatibility, a condition when the mother has Rh-negative blood and the fetus has Rh-positive blood. Early detection is important to treat the mother with Rh immune globulin and to treat her baby for hemolytic anemia.

Decompression of polyhydramnios

Polyhydramnios, or the accumulation of amniotic fluids which leads to increase risk of cesarean section, can be relieved via decompression amniocentesis. Amniocentesis can also be used to diagnose potential causes of polyhydramnios.

Preterm rupture of membranes

An emerging indication for amniocentesis is in the management of preterm rupture of membranes where measurement of certain amniotic fluid inflammatory markers may be helpful. If amniotic fluid IL-6, a marker of inflammation, is elevated, the fetus is at high risk and delivery should be considered.

Stem cells

Amniotic fluid can be a rich source of pluripotent and multipotent mesenchymal, hematopoietic, neural, epithelial, and endothelial stem cells that is safe to collect and is easily cultured.

A potential benefit of using amniotic stem cells over those obtained from embryos is that they side-step ethical concerns among anti-abortion activists by obtaining pluripotent lines of undifferentiated cells without harm to a fetus or destruction of an embryo. These stem cells would also, if used to treat the same individual they came from, sidestep the donor/recipient issue which has so far stymied all attempts to use donor-derived stem cells in therapies.

Artificial heart valves, working tracheas, as well as muscle, fat, bone, heart, neural and liver cells have all been engineered through use of amniotic stem cells. Tissues obtained from amniotic cell lines show promise for patients with congenital diseases/malformations of the heart, liver, lungs, kidneys, and cerebral tissue.

The first amniotic stem cells bank in the US is active in Boston, Massachusetts.

Risks

Amniocentesis is performed in the second trimester between the 15th and 20th weeks of pregnancy; performing this test in the first trimester is associated with increased risk of pregnancy loss and fetal congenital abnormalities. The term "early amniocentesis" is used to describe use of the process between 9 to 14 weeks of gestation.

Major risks associated with amniocentesis include pregnancy loss, vaginal bleeding or amniotic leakage after test, pre-labour ruptured membranes (aka "water breaking"), and preterm labor and delivery. Additional potential complications of amniocentesis include, respiratory distress, postural deformities, chorioamnionitis, fetal trauma and alloimmunisation of the mother (rhesus disease). Studies from the 1970s originally estimated the risk of amniocentesis-related miscarriage at around 1 in 200 (0.5%). Three more recent studies from 2000 to 2006 estimated the procedure-related pregnancy loss at 0.6-0.86%. Unlike the previous studies, the number in this study only reflects the loss that resulted from amniocentesis complications and excluded the cases when parents decided for an abortion following the test results. However, the most recent systematic analysis conducted in 2019 cites the procedure related risk of miscarriage associated with amniocentesis to be 0.30% (95%CI, 0.11-0.49%).

Amniotic fluid embolism has also been described as a possible outcome. Additional risks include amniotic fluid leakage and bleeding. These two are of particular importance because they can lead to spontaneous abortion in pregnant patients.

In spite of the aforementioned risks, the American College of Obstetricians and Gynecologists recommend that diagnostic testing options like amniocentesis be discussed with and offered to all patients that request them and that amniocentesis can be used after screening tests to confirm the presence of chromosomal abnormalities.

Social implications

The prenatal diagnosis of chromosomal abnormalities can have social drawbacks as technology changes the way people think about disability and kinship. One disadvantage associated with amniocentesis is that the results from the test are typically not available until after 17 weeks gestation. This is late in pregnancy and can result in increased emotional distress for patients who receive an unexpected fetal diagnosis. In one sense, amniocentesis offers a window of control and in another, an anxiety-provoking responsibility to make rational decisions about complex, emotional and culturally contingent issues.

Procedure

This procedure is typically performed in the outpatient setting by a team of providers. Typically at least two providers are needed for the procedure since hands must be used to hold the needle, hold the syringe and hold the ultrasound probe. With transabdominal or transvaginal ultrasound guidance, a needle is inserted into the abdomen at an angle through the muscle, into the uterus and into the amniotic cavity. The amniotic fluid is then aspirated and the fluid is analyzed for genetic abnormalities. There are various methods to obtain samples including a single needle and double needle technique. These techniques have their own variations in how they are performed including guidance of needle insertion location, and angle of needle insertion. The collected amniotic fluid is then submitted for laboratory testing for chromosomal abnormalities and the puncture site heals with time.

Ultrasound evaluation

Before the procedure is performed, the fetus is analyzed via ultrasound to determine if it is viable and for any abnormalities. The ultrasound determines the location of the placenta, fetal position and movements, and characteristics of the amniotic fluid. This information is utilized to determine the type of needle used and how the procedure should be performed.

Preparation

The abdomen is treated and cleaned with antiseptic before the procedure and/or the probe is covered with sterile coverings . Sterile gel is also used on the abdomen before scanning with a sterile ultrasound probe. These measures are taken to reduce infection risk. The tools used in the procedure are coated with heparin to prevent clotting.

Needle insertion

With the aid of ultrasound guidance, a needle is inserted through the mother's abdominal wall, then through the wall of the uterus, and finally into the amniotic sac. The physician then punctures the sac in an area away from the fetus and extracts approximately 20ml of amniotic fluid. This procedure can be performed with a single needle or a double needle technique based on individualized patient factors and physician preference. From the 20 ml of amniotic fluid, the first 2 ml is typically discarded due to mixture with maternal blood cells to ensure high quality fluid sampling.

Post procedure recommendations and analysis

If used for prenatal genetic diagnosis, fetal cells are separated by centrifugation from the extracted sample. The cells are grown in a culture medium, then fixed and stained. Under a microscope the chromosomes are examined for abnormalities. The most common abnormalities detected are Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Turner syndrome (monosomy X). The sample is also analyzed for fetal infection and for intra-amniotic inflammation through infection studies.

After the procedure, the patient is instructed to take house rest for the initial 24 hours post-procedure however normal activities are allowed such as personal hygiene. In regard to the fetus, the puncture seals and the amniotic sac replenishes the liquid over the next 24–48 hours. One week after the procedure, the mother will have a follow up appointment for ultrasound analysis to confirm fetal viability and to assess healing of the puncture site.