Overview of Amniocentesis
Before a baby is born, doctors can do tests to identify a wide array of abnormalities and conditions. These issues might be related to the baby’s chromosomes, genes, spine, or even infections that could affect the baby’s health. They use different techniques such as amniocentesis, chorionic villus sampling, and fetal blood sampling for this purpose.
Amniocentesis is a procedure where fluid from the womb, known as amniotic fluid, is taken out with a needle. The doctor uses an ultrasound to guide them. This test was first used in 1956 to identify the sex of a baby while it was still in the womb. It’s now used to test for many different health issues by examining the cells, chemicals, and bacteria in the fluid. It can also be used to lower the amount of fluid in the womb in certain medical situations.
The amniotic fluid collected contains many substances like cells shed by the baby, fluid that has come through the baby’s skin, urine from the baby, and substances produced by the baby’s lungs. This test carries a small risk of loss and is usually done after 15 weeks of pregnancy.
Like any medical procedure, amniocentesis comes with potential risks and benefits. It is important for the parents to have an understanding of why the test is being done, what it involves, and what the results could mean. This understanding can help them make a decision that aligns with their personal, ethical, and religious beliefs about pregnancy, as well as legal requirements.
Chorionic Villus Sampling, or CVS, is another way doctors can identify genetic and chromosomal disorders. It is done between 10 to 14 weeks of pregnancy with the help of ultrasound. The test involves taking a small tissue sample from the part of the womb that becomes the placenta. The results generally come back within 7 to 10 days. However, there are risks involved due to the invasive nature of the procedure.
Last but not least, there’s fetal blood sampling (also known as cordocentesis). In this procedure, doctors collect a sample of the baby’s blood from the umbilical cord while the baby is still in the womb. It’s usually performed after 18 weeks once the cord is clearly visible on ultrasound; however, it’s safer to perform the procedure between 20 to 28 weeks. The results of the test are usually available between 24 and 72 hours. This procedure carries the highest risk of fetal loss compared to the previous two procedures. It’s most commonly used when there is an issue with the mother’s blood reacting against the baby’s blood, which can happen after a blood transfusion or a previous pregnancy.
Anatomy and Physiology of Amniocentesis
Amniotic fluid, which is clear, slightly yellow in color, is a crucial element of a pregnancy. This fluid can be found inside the amniotic sac, providing a comfortable environment for a baby to grow in the womb. Among its functions are encouraging movement, which aids in skeletal growth, and facilitating the baby’s swallowing and breathing in the womb.
Here’s a brief look at how it forms:
Starting from the 8th day of pregnancy, changes begin to happen in the building blocks of the baby, known as the trophoblast. A formation called the bilaminar germ disc is created after some parts of the baby start to differentiate or become more developed. On one side of this disc, we find tall cells that originate from the ectoderm layer of the developing baby. The other side of the disc features flattened cells from the endodermal layer. The disc is connected to the trophoblast by what’s known as a connecting stalk, which later becomes the umbilical cord. Two cavities then appear on either side of this disc: the amniotic cavity and the yolk sac.
The amniotic fluid is created by maternal and fetal compartments in the first months of pregnancy. To get a better picture of this, it’s important to understand that the skin of a baby in early development stages is non-keratinized, meaning it doesn’t have a protective cell layer yet. This state allows small molecules and water to freely pass through into the amniotic sac, which makes up the amniotic fluid. The fluid then acts as a balanced environment for the growing baby.
As the pregnancy progresses into the second trimester, the baby’s skin undergoes keratinization, meaning it starts to develop a layer of protective cells. This makes the baby’s skin impervious to water and other molecules, halting the transfer of more substances into the amniotic fluid.
On scans, at about nine weeks, urine can be seen in the baby’s bladder. By this phase, urine becomes the primary component of the amniotic fluid. The urine has low concentrations of certain substances (80 to 140 mOsm/liter), and as the baby’s kidneys grow, the urine contains more urea, uric acid, and creatinine. At full term, the baby contributes about 500 to 700 ml of urine per day into the amniotic fluid.
The volume of amniotic fluid averages about 60 ml at 12 weeks of pregnancy. By 16 weeks, the volume increases to around 175 ml. From 20 weeks forward, the quantity of amniotic fluid rises gradually. Its volume reaches between 400 to 1,200 ml at around 34 to 38 weeks. The net increase of the fluid is about 5 to 10 ml/day during the third trimester. After 38 weeks, the volume shrinks by about 125 ml/week to an average of 800 ml at full term of 40 weeks.
Why do People Need Amniocentesis
Amniocentesis is a procedure performed for various reasons. It generally falls under two categories: diagnosis and treatment.
Diagnostic Reasons:
Chromosomal Analysis:
Amniocentesis can diagnose problems with the baby’s chromosomes and genes. These tests analyze the baby’s DNA and can help identify things like inherited diseases, conditions linked to the baby’s biological sex, and disorders affecting the baby’s metabolism. Doctors might recommend these tests in certain situations like:
- If the mother is aged 35 or above
- If lab tests done during pregnancy show abnormal results
- If an ultrasound finds certain physical abnormalities in the baby
- If there were chromosomal abnormalities in previous pregnancies
- If either parent has a chromosomal abnormality
Genetic Testing:
Amniocentesis can assess the level of certain proteins, like Alpha-fetoprotein and Acetylcholinesterase, to detect potential genetic conditions.
Assessment of Rh Factor:
In situations where the baby’s blood type is not compatible with the mother’s, amniocentesis can determine how serious the issue is.
Fetal Infections:
Amniocentesis can be used to check for infections in the baby. These could include conditions like CMV, parvovirus, and toxoplasma gondii.
Lung Maturity:
Amniocentesis can be done in the later part of pregnancy to check if the baby’s lungs are mature enough for the baby to breathe on its own after birth.
Chorioamnionitis:
Amniocentesis can diagnose a condition called chorioamnionitis, which is an infection of the amniotic fluid and the tissues surrounding the baby.
Bleeding Disorders:
Amniocentesis can help identify more severe genetic bleeding conditions, such as Hemophilia A and B or type 3 von Willebrand Disease, to prevent possible complications during delivery.
Therapeutic Reasons:
In certain cases, amniocentesis can also be done as part of treatment:
- Excess fluid within the womb can cause discomfort for the mother. Removing this fluid can provide relief and allow for the administration of medications directly into the womb.
- For twin pregnancies with uneven fluid, the amniocentesis process can relieve pressure, bettering the flow of nutrients from the placenta and improving outcomes for the baby.
- In cases with a lack of amniotic fluid, fluid can be injected via amniocentesis to protect the baby’s lungs and prevent compression of the umbilical cord during labor.
- If a baby has severe blood-related issues, amniocentesis can enable a blood transfusion to the baby even before birth.
When a Person Should Avoid Amniocentesis
There’s no situation where amniocentesis, a test done during pregnancy, is strictly not allowed.
However, there are situations where this test might not be the best choice:
1. If a woman has Hepatitis B or HIV, these infections can be passed to her baby during the test. For women with HIV, the test should ideally be postponed until after they start taking medicine that lowers the virus count in their bodies. This kind of HIV medicine is highly effective at preventing the virus from passing from a mother to her baby.
2. If there’s not enough amniotic fluid surrounding the baby (a condition known as oligohydramnios), doing the test might also not be ideal. Amniotic fluid is like the baby’s cushion, providing protection and helping them grow.
3. This test is not suitable if a woman is taking a medicine to prevent blood clotting. This type of medication needs to be stopped 48 to 72 hours before the procedure. In the meantime, these women might be shifted to a different type of blood-thinning medication known as low molecular weight heparin.
Equipment used for Amniocentesis
The procedure is carried out under constant supervision and direction of an ultrasound machine. This allows the doctor to view inside your body in real-time for the best results. Here is a list of equipment that needs to be available:
1. An ultrasound machine – a device that uses sound waves to create images of the inside of your body.
2. Sterile swabs and drapes – these are clean materials used to clean the skin and cover the patient to maintain a clean environment and prevent infection.
3. Syringes (of 2 ml and 10 ml sizes) – these are tools used to inject or withdraw fluids from the body.
4. A 20 to 22 gauge needle – a slim, hollow tool used for injections or to get samples of tissue or liquid from your body.
5. Containers – used for collecting samples during the procedure and safe transportation afterwards.
6. 5% povidone-iodine solution – an antiseptic solution often used to clean the skin before a procedure to prevent infections.
Who is needed to perform Amniocentesis?
If couples are planning to have a baby, it’s a good idea to visit a genetic counselor. This expert can explain whether they might pass down any genetic diseases to their baby, helping them make informed decisions.
Just like any other medical procedure, they should also sign an informed consent form. This just means they agree to the procedure after a thorough discussion about what it means – don’t worry, the doctor will explain everything!
The doctor will discuss all the aspects of the procedure. This discussion will include the good and the bad, the reasons for the procedure, what will happen during the procedure, and any possible problems for the mother or baby. He or she will give detailed explanations about anything that could happen to the baby or the mother. They will explain how long it takes for results to come, what it means if the cells they collect can’t be grown for the test, and the kind of genetic test they’ll do on the sample.
The doctor will keep a record of the procedure and write how many times a needle was inserted. This is important for their records.
A pregnancy ultrasound or scan is done before this procedure. This scan helps the doctor see how many babies there are, whether they’re healthy, where the placental (a structure that provides oxygen and nutrients for the baby) is located, the gestational age (how far along the pregnancy is), where the cord is attached, and if there are any obvious physical issues with the baby.
The doctor who will do the procedure must have enough experience, which means they’ve done at least 20 similar procedures under supervision. If they’re doing this test on a pregnancy with more than one baby, they should have high-level skills in understanding pregnancy anatomy, accurately collecting samples, and potentially ending the pregnancy of an identified baby if needed.
Preparing for Amniocentesis
Before beginning the medical procedure, both the doctor and the assistant need to clean their hands thoroughly using a special germ-killing solution, and put on sterilised gloves. The part of the patient’s stomach that will be worked on also needs to be cleaned. This is done using a special antiseptic solution called povidone-iodine and sterile bandages soaked in antiseptic.
Even though many procedures require local anesthesia, which is a medicine used to numb a specific area of the body, it’s not needed here. Also, preventive antibiotics, medications that help stop infections before they start, aren’t necessary in this case.
In women who have a specific blood type known as Rh-negative, a medicine called anti-D immunoglobulin needs to be given. This drug helps prevent potential complications associated with the Rh blood type.
For this procedure, an ultrasound device is used. This is a tool that uses sound waves to create images of the inside of the body. The ultrasound probe needs to be covered with a sterile plastic cover for safety and to avoid any contamination. A special gel is applied to the inside of the cover, which helps the ultrasound waves travel better into the body. Ideally, this gel should also be sterile to further decrease the risk of any unwanted germs spreading.
How is Amniocentesis performed
Amniocentesis is a test done in a clinic that checks the health of your baby while they are still in your womb. Before the test, you will receive counseling to help you understand what the test is for and what the results could show. You will also be asked to sign a form saying you understand this and agree to the test.
The doctor will perform an ultrasound, which uses sound waves to create a picture of your baby inside your womb. During the ultrasound, they will check the baby’s age, the location of the placenta (which provides the baby with nutrients), and if there are any visible birth defects. The doctor will also check the position and movement of the baby, the baby’s heartbeat, and the amount of amniotic fluid (the fluid that surrounds the baby in your womb).
After the ultrasound, the area of your skin where the needle will be inserted will be cleaned with an antiseptic. Once everything is ready and has been checked, the doctor will carry out the amniocentesis. They will use a long thin needle to take a sample of your amniotic fluid. The needle is guided by the ultrasound to make sure it doesn’t touch the baby. Ideally, the needle will go in at a right angle to your skin. It can be a little less uncomfortable if the needle is inserted in the upper part of your womb.
The doctor will make sure not to insert the needle through the placenta or close to the baby or the umbilical cord, which provides the baby with nutrients and oxygen. If there’s a risk of infection, such as HIV or Hepatitis B or C, it’s even more important not to go through the placenta.
Once the needle is in the right spot, the doctor will carefully draw out some of the amniotic fluid. This fluid contains cells from the baby, which can be tested in a lab. The first bit of fluid is usually not used, because it can contain cells from the mom, which can give a false result. Normally, about one or two tablespoons of fluid is taken for the test. After enough fluid has been collected, the needle is removed.
It’s important that the baby is doing well after the test, so the doctor will keep checking their activity and heartbeat. You’ll also be able to see this on the ultrasound.
If you’re expecting twins, the process can be a bit more complex. The doctor might use two needles or use a special dye to make sure they get fluid from each baby.
After the test, you might be checked on for a little while before going home. You’ll need to take care and tell your doctor if you notice any signs of complications like fluid leakage, bleeding, pain, or fever. You should avoid heavy exercise, but otherwise can go about your normal activities.
Without using an ultrasound to guide the needle, these tests can sometimes fail, meaning no fluid can be collected. If this happens, your doctor will have to try again.
Remember, amniocentesis is a very safe procedure, but as with any medical procedure, there can be risks. However, your doctor will be sure to explain anything you need to know and answer your questions before your test.
Possible Complications of Amniocentesis
Amniocentesis, a medical procedure used to examine the baby in the womb, can sometimes cause problems for both the mother and baby.
For Mothers:
– There’s around a 2.6% chance that the mother’s and baby’s blood could mix, which isn’t supposed to happen.
– Moms with an Rh-negative blood type may have complications.
– It’s unlikely, but skin bacteria could possibly enter the liquid around the baby, causing an infection. This only happens about 0.1% of the time.
– The procedure can sometimes cause premature labor if done in the third trimester. Other common issues are the breaking of water too early and too little amniotic fluid.
– Vaginal bleeding can occur in 2% to 3% of cases.
– Some mothers may experience pain or discomfort after the procedure.
– Although extremely rare, sometimes the amniotic fluid could enter the mother’s bloodstream, causing serious complications.
– Very rarely, injuries to the mother’s skin or internal organs can occur as a result of the procedure.
For Babies:
– There’s a 0.11% chance that the baby could be lost because of the procedure. This risk increases for women at higher risk of miscarriage, like those with overweight issues, fibroids, vaginal infections, or babies with structural issues.
– Sometimes, the amniotic fluid leaks, which happens in 1% to 2% of cases. Most of the time, it seals on its own. But, in some cases, it might lead to underdeveloped lungs in the baby, causing breathing problems.
– Baby injuries may occur, including bleeding from the umbilical cord, injuries to their eyes, and deformities like clubfoot.
– If the doctor needs to prick more than three times to obtain fluid, the risk of complications is higher. Ideally, if an adequate sample is not obtained in two pricks, the doctor should stop and try again after 24 hours. The risk is lower when the procedure is conducted by experienced practitioners, who perform more than 300 procedures a year.
What Else Should I Know About Amniocentesis?
Amniocentesis is a procedure where a sample of the amniotic fluid surrounding a baby in the womb is taken for testing. This is usually a safe procedure, but the location of the placenta can impact the process. Ideally, the needle used to remove the fluid should avoid penetrating the placenta to minimize complications. If the placenta is towards the front and top of the uterus, this could lead to more complications like multiple needle pricks and bloody amniotic fluid. Penetrating the placenta can also slightly increase the chances of giving birth prematurely. However, the risk of losing the baby does not increase.
Once the amniotic fluid is collected, it’s taken to a lab where tests are carried out to check for genetic and chemical abnormalities. These results may take up to three weeks to come back.
Two of the most common tests done on amniotic fluid include the rapid test and the full karyotype. The rapid test checks for certain chromosomes that could indicate conditions like Down’s syndrome, Edward’s syndrome, and Patau’s syndrome; these conditions can cause physical and mental abnormalities. The rapid test is almost 100% accurate and results are available in 1-2 days.
The full karyotype takes longer. Scientists grow cells from the amniotic fluid in a lab for up to 10 days before looking at them under a microscope. This allows them to check the number and appearance of the baby’s chromosomes.
There are also less common tests, like the Chromosomal Microarray, which can detect certain abnormalities in the baby’s chromosomes. These abnormalities may not show on a normal ultrasound examination and can be found even when the standard chromosome test (karyotype) is normal. Besides, there are specialized tests that help diagnose specific genetic conditions.
Some attributes of the amniotic fluid itself can also be tested. The presence of certain proteins and compounds helps in identifying conditions like open neural tube defects. Additionally, if the fluid is cloudy or discolored, it should be tested for the presence of bacteria to make sure there’s no infection. Antibiotics can be given if necessary.
It’s important to realize that for most chromosomal conditions, there’s no cure. This means parents need to be offered appropriate counseling and support when considering whether to continue the pregnancy.