While amniocentesis itself is a simple procedure, the test is very emotionally demanding for parents. Amniocentesis is performed soon after the first movements of the baby are felt.
The test is designed to detect about forty of the approximately four hundred known fetal abnormalities. In many cases parents will be forced to choose between keeping a child who will be born with a life-long condition or terminating the pregnancy.
The test can also determine the baby's sex, although it is not used for that purpose except when it could predetermine a genetically linked disorder such as hemophilia. The test is used to confirm the presence of certain fetal abnormalities that may have been suggested by an alphafetoprotein test or nuchal scan.
During the early part of your pregnancy the cells that line the amnionA membrane that surrounds the amniotic cavity, covering the fetal side of the placenta and the outer surface of the umbilical cord. It also becomes the outermost layer of skin on the developing fetus.
Visit our comprehensive glossary for more pregnancy terms and definitions., the stretchy sac that surrounds the fetus makes the amniotic fluidThe liquid, which is produced by both the fetal membranes and the fetus that surrounds the baby during pregnancy. The liter of fluid at term serves to protect the fetus during pregnancy and also provide active chemical exchange.
The amniotic fluid consists of maternal and fetal plasma in varying concentrations. The pH of the fluid is almost neutral and clear, although lipids and desquamated fetal cells can make it cloudy.
Visit our comprehensive glossary for more pregnancy terms and definitions.. Around week twelve the baby takes over as it swallows the existing fluid and passes it, adding a little more as it does so. As the baby moves in what is essentially its own recycled urine, cells are removed and lie suspended in it. The same thing happens when you bathe: if you take a sample of your bathwater you would probably find some of your cells in it.
Amniocentesis involves removing a small sample, about ½ to 1 oz (15 - 30 ml) of the amniotic fluid and examining the cells. Your doctor will require that you have a full bladder before beginning the procedure since the uterus needs to be properly positioned before removing the sample. Using ultrasound, your doctor will locate an area in the uterus that is unobstructed by the fetus and the placentaThe placenta is a large disk shaped membrane responsible for providing nourishment to the fetus during pregnancy. It consists of three parts, the fetal part made up from the chorion membrane surrounding the fetus, the maternal part, formed from the decidua basalis layer of the uterine lining, and the intervillous space between the two plates. It is connected to the fetus by the umbilical cord and consists of tissue from both the mother and the embryo.
Its function is complex. It has been described as a simple organ that combines the functions of a kidney-dialysis machine, heart and lung machine and intravenous drip. It consists of enormous numbers of blood vessel branches that permit the exchange of nutrition and oxygen, from the mother's bloodstream to the fetus and the removal of wastes to the mother to be excreted. The placenta's remarkable quality is that it does so without the blood of the mother mixing with that of the baby.
It also is responsible for the production of vital hormones including, estrogen, progesterone, and human chorionic gonadotropin. After birth, the placenta is delivered, and is sometimes referred to as the afterbirth.
Visit our comprehensive glossary for more pregnancy terms and definitions.. The abdomen is cleaned and numbed with local anestheticAn agent or process that removes the body's sensitivity to pain. Anesthetics are usually medically administered chemicals, although they include other forms such as hypnosis, or the body's own ability to cause numbness through shock.
Anesthetics can either be local, whereby only a portion of the body or an individual organ is desensitized or general, in which the entire body is desensitized, with the result the patient is often temporarily unconcious.
Visit our comprehensive glossary for more pregnancy terms and definitions. and a long hollow needle is inserted through the abdomen into the uterus. The fluid is withdrawn using a syringe.
Once removed, the fluid is spun in a centrifuge to separate the fetal cells from the amniotic fluid. These cells are removed and grown in cultures before being examined through a microscope to identify if any fetal abnormalities are present.
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The little hole in the amniotic sac usually closes up by itself very quickly. If it doesn't amniotic fluid may slowly leak out. While not unusual during the first few hours, if it continues you should tell your doctor right away. Such leaks do not often cause problems but they should be carefully monitored. Occasionally a woman will complete her pregnancy while continuing to leak small amounts of fluid with no harm to the baby. If you are Rh-negative you should have an Rh-immune globulin injection after amniocentesis.
It is important to understand that amniocentesis is designed to confirm the presence of fetal abnormalities suspected as a result of an alphafetoprotein test, ultrasound or nuchal scan. The implications of a positive result should not be taken lightly and if you are thinking about amniocentesis you should consider talking to a counsellor before accepting the test.
The test is reserved for women who have high risk pregnancies. This includes women who will deliver their baby after their thirty fifth birthday, have a history of a baby with a birth defect, a birth defect themselves, a family history of birth defects or a partner with a birth defect. Certain genetic disorders such as Tay-Sachs disease and sickle cell anemia, or chromosomal disorders such as Down's syndrome are high risk factors.
Some diseases such as hemophilia or one type of muscular dystrophy can only be passed onto a male child. In fifty percent of cases a serious illness will develop. During the early part of your pregnancy you will have received screening to determine if you are a carrier for those diseases linked with the female x-chromosome. In the past screening for this type of high risk pregnancy also included diabetes, a condition in which amniocentesis was used to determine the maturity of the fetal lungs. A decision could then be made whether to induce labor although this practice is now more commonly replaced with ultrasound dating and careful monitoring.
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If you are subject to convulsions and using medications such as phenytoin or valproic acid to control seizures your doctor will have discussed with you the risk of neural tube defectsAny of a group of congenital malformations that involve the skull and the spinal column. Most commonly it involves the failure of the neural tube to close properly during embryonic development.
High levels of alphafetoprotein in the amniotic fluid can reveal potential problems prenatally, and the fetus can be scanned using ultrasound. Immediate surgical repair is required.
Visit our comprehensive glossary for more pregnancy terms and definitions. associated with these drugs.
Amniocentesis is a wonderful tool during a high risk pregnancy that can be used to provide a window into the uterus and monitor the development of the fetus. But knowledge is a double-edged sword and before you commit to amniocentesis consider why you may want to refuse it.
Many people feel strongly about abortion for ethical, moral or religious reasons. The right of a child to live even if born with a genetic disorder must be carefully considered. You may decide that amniocentesis can provide you and your family the time to prepare for the baby and help you make certain decisions about the delivery of the baby.
Of all the invasive tests, amniocentesis performed by an experienced doctor has proven to be the safest. The risk of miscarriage is about 1% (1 in 100) although some studies report a risk as low as 0.2% (1 in 500). This risk must be weighed against the general risk, about 4% (1 in 25) of a baby born with a deformity. Some studies have suggested that amniocentesis is responsible for respiratory difficulties in about 1% (1 in 100) procedures. This is a matter of debate and you should discuss it with your doctor before having the test.
The use of ultrasound while performing amniocentesis has dramatically improved the safety of the test and the fetus, umbilical cord and placenta are rarely struck by the needle. Occasionally temporary cramping, slight bleeding and leakage of amniotic fluid may occur and in about 0.1% (1 in 1000) examples anmioitis, an infection in the amniotic fluid, may result. You should always report an increase in body temperature after amniocentesis just in case.
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In about 1% (1 in 100) procedures the cell samples will fail to culture. Rarely, in about 0.17% (1 in 600) procedures, an unusual problem is maternal cell contamination, in which the mother's cells are found in the fluid. If these problems occur time is against you and you will need to decide how much a definitive answer is worth to you. It is possible to ensure an accurate result is through karyotyping: chromosome analysis that includes counting and looking for structural changes. Karyotyping would require a second amniocentesis and many women decide not to pursue this option late in pregnancy. Another alternative is cordocentesis, a specialized procedure that removes fetal blood from the umbilical cord.
If a second amniocentesis is performed near term there is a slight chance that the membranes will rupture and labor may be initiated. If you are screening for Down's syndrome on the basis of maternal age alone at this stage in pregnancy you should consider a detailed ultrasound scan as an alternative. While the ultrasound will only screen and cannot provide a definitive answer regarding the presence of Down's syndrome, it is safer during later pregnancy.
Amniocentesis takes from 10 - 20 minutes to perform. Once the fetal cells are separated, they are grown in cultures for two weeks and the results are usually received three weeks after the operation. The test is typically performed by week sixteen, so that the results can be returned by week twenty leaving parents the option to terminate the pregnancy if they choose. At this stage in the pregnancy an induced labor is the only option and it is an unpleasant experience. This is a distressing decision to make since the first fetal movements will almost certainly have been felt by the time the test is taken. The three week wait between the test and receipt of the results is a time of considerable stress, and many women talk about 'putting their pregnancy on hold' during this time. Parents who are going through this experience will need as much emotional support as their family can provide.
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Experiments have been made with amniocentesis as early as week nine. There are many concerns about an increase in the rate of respiratory disease at birth as a result of removing amniotic fluid this early in pregnancy. Since less fluid is available during early pregnancy about 21% (1 in 4) cell cultures fail to grow and the test will need to be repeated. The risk of miscarriage also increases, between 3% and 7% (3 in 100 to 7 in 100), depending on the skill of the doctor.
Once the cell cultures have developed a laboratory can determine considerable information from them. Using chromosome analysis or karyotyping, the chromosome count and structure can be examined to discover whether the fetus has a disability. If there is a risk of a genetically linked disorder that affect 50% of male children, the cells will be examined through a microscope to discover the sex of the fetus.
Separate analysis of the amniotic fluid can confirm the presence of metabolic disorders that are caused by missing or defective enzymes. The amount of bilirubinThe broken down red blood cells converted into non-toxic substances in the liver from the hemoglobin. Newborns may have levels of pigment too high for the liver to convert. Also known as bile pigment.
Visit our comprehensive glossary for more pregnancy terms and definitions. in the amniotic fluid will determine if the baby is Rhesus positive and whether an intrauterine transfusion will be necessary.
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If there is uncertainty about the age of the fetus, the laboratory will measure the ratio of lecithin to sphingomyelin (L/S ratio) in the amniotic fluid to verify the maturity of the lungs. Gasses disolved in the amniotic fluid can also be measured to ensure that the baby is receiving enough oxygen. This can be confirmed by measuring the acidity of the fluid to verify that there is no sign of fetal distress as a result of inadequate oxygen.
Waiting for the results of the test to arrive is a miserable and distressing experience. Your doctor and the staff in the hospital or facility you are attending will attempt to support you as best they can. You should consider counselling to prepare you for the results of the test, and it should be immediately available for both parents if a test returns positive.
For some parents, termination of the pregnancy will be the only option. Ask your doctor to recommend a support group designed for parents who face termination because of abnormalities. Try not to feel pressured into making a quick decision and spend as much time as you can considering your options.
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