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Amniocentesis



Why Get Tested

To detect and diagnose certain birth defects genetic diseases and chromosomal abnormalities in a fetus especially if maternal serum screening tests are abnormal to evaluate fetal lung maturity when there is an increased risk of premature delivery sometimes to diagnose a fetal infection occasionally to help diagnose and monitor hemolytic disease in a fetus

When To Get Tested

Between 15 and 20 weeks of gestation to test for genetic diseases chromosomal abnormalities and open neural tube defects after 32 weeks to evaluate fetal lung maturity when it is suspected that a fetus has an infection or other illness serially about every 14 days when it is suspected that a pregnant woman has an Rh or other blood type incompatibility with her fetus

Sample Required

A sample of amniotic fluid obtained using a procedure called amniocentesis

Test Preparation Needed

You may be instructed to have either a full or empty bladder prior to amniocentesis depending on when during your pregnancy the testing is being performed follow any instructions you are given




Common Questions


Amniotic fluid analysis may used for several different purposes and the specific testing that is done depends on the reason for testing The following list includes some of the more common ways that this analysis may be used To detect chromosomal abnormalities or genetic disorders Chromosome analysis a cytogenetics test that may also be called karyotyping Chromosome analysis will detect chromosomal abnormalities associated with a variety of disorders It evaluates the 22 paired chromosomes and the sex chromosomes X Y in the nucleus of cells cultured from those collected in the sample of amniotic fluid and can be used to diagnose a variety of disorders including Down syndrome Trisomy 21 caused by an extra chromosome 21 in all or most cells of the body Edwards syndrome Trisomy 18 associated with severe mental retardation caused by an extra chromosome 18 Patau syndrome Trisomy 13 caused by an extra chromosome 13 Klinefelter syndrome the most common sex chromosome abnormality in males caused by an extra X chromosome Turner syndrome caused by missing one X chromosome in females Due to the nature of this type of testing chromosome analysis can also definitively determine the sex of a fetus Genetic testing also called molecular testing It looks at fetal DNA to identify specific gene mutations and diagnose a variety of inherited diseases Each test is ordered separately based upon the parents personal and family histories If a specific gene mutation is known to be present in the mother s or father s family then that specific gene mutation can be tested for While there are hundreds of genetic tests that can be performed only a few are associated with relatively common disorders Typically only the most common mutations are tested therefore a fetus could still have an inherited disorder even though genetic testing did not identify one A few examples of genetic tests more frequently performed include those for Cystic fibrosis Tay-Sachs disease Canavan disease Familial dysautonomia Sickle cell anemia Thalassemia To detect birth defects Testing for open neural tube defects NTDs such as spina bifida or anencephaly detects chemicals that may be present in abnormal quantities when a fetus has an anatomic abnormality For example AFP alpha-fetoprotein is increased with neural tube defects Acetylcholinesterase is increased with neural tube defects and also other anatomic abnormalities To evaluate fetal lung maturity Testing to evaluate fetal lung maturity may be performed if a woman is at an increased risk for premature delivery or an early birth is necessary for the baby or mother s health The tests are based upon the presence of adequate protective liquid substances called surfactants in the lungs which are necessary for proper lung function If there are insufficient surfactants a newborn may develop life-threatening neonatal respiratory distress syndrome RDS Tests include Lamellar body count Phosphatidylglycerol PG Lecithin sphingomyelin L S ratio To detect Rh and other blood type incompatibilities and diseases When a mother has been previously exposed through prior pregnancies or blood transfusions to red blood cell antigens that she does not have on her own red blood cells she may develop antibodies against those red cell antigens become sensitized If the antigens are present on the red blood cells of the fetus inherited from the father then the fetus is at risk for a maternal-fetal incompatibility The mother s antibodies can cross the placenta and bind to and destroy the fetus s red blood cells causing hemolytic anemia An affected fetus can be born with hemolytic disease of the newborn One of the most commonly encountered incompatibilities is due to ABO group differences but there are many other blood types that may also cause this problem Tests for bilirubin may be performed on a regular basis starting at about 25 weeks of pregnancy to detect evaluate and monitor the severity of the hemolytic anemia in a fetus To evaluate fetal distress Evaluation of amniotic fluid color may be indicative of fetal distress To detect fetal infections There are a few tests that can be performed on amniotic fluid to detect infections that are passed from mother to baby during pregnancy congenital infections Some of these infections may have serious consequences for the developing fetus A few examples include tests for Cytomegalovirus CMV Toxoplasmosis Parvovirus B19 Fifth disease Cultures for bacterial infections

While amniocentesis is safe and has been performed for many years it is an invasive procedure that poses a slight risk of injury to the fetus and of miscarriage For this reason it is not performed routinely with each pregnancy Genetic amniotic fluid analysis may be offered as part of second trimester prenatal testing and is performed primarily between 15 and 20 weeks gestation if A woman is 35 years of age or older A woman has an abnormality on a first trimester Down syndrome screen or second trimester maternal serum screen such as an increased or decreased alpha-feto protein AFP level A woman had a previous child or pregnancy with a chromosomal abnormality or birth defect There is a strong family history of a specific genetic disorder A parent has an inherited disorder or both parents have a gene for an inherited disorder An abnormality has been detected on a fetal ultrasound Fetal lung maturity amniotic fluid testing is ordered when there is a risk of premature delivery at any time after 32 weeks gestation Biochemical testing is sometimes ordered to monitor bilirubin levels when a woman has been sensitized or it is suspected that she has become sensitized has developed antibodies to red blood cell antigens and there may be an Rh or other blood type incompatibility with the fetus In this case serial testing for bilirubin may be performed usually about every 14 days An amniotic fluid analysis may be performed in late pregnancy to check for fetal distress and to diagnose a fetal infection

Genetic tests chromosome analysis and testing for birth defects Women should discuss their test results with their health practitioner and with a genetic counselor If a chromosomal abnormality or a genetic disorder is detected then the baby likely will have the associated condition However test results may not predict the condition s severity or prognosis Normal results make it less likely that a fetus has an inherited condition but all genetic conditions cannot be ruled out Not every genetic disorder or chromosomal abnormality will be detected with this testing If an increased or decreased alpha fetoprotein suggests a structural abnormality such as an open neural tube defect then additional testing and imaging may be performed to determine the severity of the condition and the best course of action Fetal lung maturity If testing indicates that there are low levels of surfactants then a fetus s lungs have not yet matured and measures can be taken to attempt to delay delivery to promote lung maturity and when necessary to treat the baby as soon as it is born If the levels of surfactants are deemed high enough then the baby may be safely delivered without increased risk of complications from lung immaturity Rh or other blood type incompatibility Increasing bilirubin concentrations in a fetus with a fetal-maternal blood type incompatibility indicate increasing destruction of red blood cells RBCs and the likelihood that the fetus will be born with hemolytic disease of the newborn requiring treatment depending on the severity Fetal distress or infection Evaluation of amniotic fluid color Green-tinged indicates that meconium the fetus s first stool has been released Yellow to amber may indicate bilirubin in the fluid Red-tinged indicates blood from the mother or the fetus Cultures of the amniotic fluid will indicate whether or not an infection is present

Both blood contamination and stool from the baby meconium in the amniotic fluid can affect some chemical test results An alternative to amniotic fluid analysis for chromosomal analysis and genetic testing is chorionic villus sampling CVS which can be performed earlier between 10 and 12 weeks of pregnancy This first trimester procedure collects a placenta tissue sample at the site of implantation and carries about the same risks as amniocentesis CVS cannot however detect neural tube defects Performed on a blood sample obtained from the mother the first trimester screen for Down syndrome and the second trimester screen for Down syndrome and open neural tube defects assess the risk of a fetus having these conditions but are not diagnostic In most cases the subsequent amniotic fluid analysis will be normal only a small percentage of those with an abnormal blood screening test result will actually have an affected baby

Amniocentesis is the removal of a small amount of fluid about an ounce from the sac that surrounds a developing fetus using a needle and syringe Before the procedure ultrasound is used to find the position of the fetus in the womb The area on the mother s abdomen is cleaned and a local anesthetic is applied to or injected into the skin During the procedure the needle is inserted through the walls of the abdomen and uterus and into the thin-walled sac of fluid that surrounds the developing fetus A small amount of amniotic fluid is withdrawn and sent to a laboratory for analysis Depending on the specific tests being performed results may be available within a few days to 2 weeks or in the case of fetal lung maturity testing within a few hours There is a slight risk with amniocentesis that the needle inserted into the amniotic sac might puncture the baby cause a small amount of amniotic fluid leakage following the procedure cause a uterine infection or in rare cases cause a miscarriage

Genetic and chromosomal abnormalities cannot be prevented The risk for open neural tube birth defects can be minimized by a woman getting plenty of folic acid prior to and during pregnancy The number of women with Rh sensitization has greatly decreased since injections of Rh immune globulin RhoGam to prevent the formation of Rh antibodies became routine in prenatal and postnatal care

The decision is best made by a woman and her health care provider together The American College of Obstetricians and Gynecologists ACOG recommends that all pregnant women should at least be given the option of having amniocentesis performed The slight risks associated with amniocentesis must be weighed against the information gained Speaking with a genetic counselor may also be helpful to learn more about the testing included in amniotic fluid analysis and what to expect from the information that can be learned

No the testing requires specialized equipment and training to interpret It needs to be performed in a laboratory and may need to be sent to a reference laboratory However the procedure for collecting the amniotic fluid can be done in an outpatient setting such as a health practitioner s office

There is a newer test called cell-free fetal DNA cffDNA that only requires a blood sample from the pregnant woman and can be used to screen for certain fetal chromosomal abnormalities including Down syndrome Edwards syndrome and Patau syndrome trisomy 13 It can be performed as early as the 10th week of pregnancy Several organizations support its use in pregnant women at high risk of having a child with a disorder caused by an abnormal number of chromosomes However invasive diagnostic tests such as amniocentesis and chorionic villus sampling CVS are still needed to confirm the results The test is also still seen as experimental by many insurance companies so the test may not be a covered expense and it may not be available everywhere

Yes Separate testing may be performed to evaluate the quantity of amniotic fluid that surrounds a fetus Too little oligohydramnios early in a pregnancy can cause birth defects or miscarriage Late in a pregnancy it can cause poor fetal growth or even stillbirth Too much amniotic fluid polyhydramnios may cause few symptoms When it is severe however it may affect a pregnant woman s breathing and increase the risk of premature birth and postpartum hemorrhage