Amniocentesis

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Precap
Amniocentesis is a prenatal test that can check for many genetic conditions and baby’s sex using aspirated amniotic fluid.

Inside your womb, the baby has a bag with fluid cushioning and supplying nutrients to your baby. Amniotic fluid has fetal cells and proteins that your baby makes. These markers can tell about the possibility of your child having any genetic disease in the course of a lifetime. Downs Syndrome is the most concerning disorder doctors look for.

The family history of genetic defects makes it mandatory for getting an amnio. Removal of fluid poses a risk of miscarriage from injury or puncture. Even though the test is diagnostic, it’s the parent’s choice whether or not to take it.

Some parents willingly chose to go ahead with a high-risk pregnancy, whatever be their reason. In their case, such tests only help them prepare for coping with the responsibilities. Others may look for options like medical termination of pregnancy MTP after getting results diagnosing a fetus with chromosomal aneuploidies.

Amniocentesis Test During Pregnancy
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Amniocentesis Test During Pregnancy

What is amniocentesis?

A prenatal test, amniocentesis is an invasive genetic test1 done in the 15-20th week of pregnancy. Doctors can determine the sex of the baby too using amnio. Accurately it can give you a clear picture of the genetic status of your baby.

Amniotic fluid is present all around your baby giving buoyancy. An obstetrician puts a fine needle, using an ultrasound transducer as a guide, into the sac to take out amniotic fluid. Only a small volume like 30mL is enough. Floating cells and cell-free DNA both have genetic information. Pregnancy-associated proteins and hormones present in the fluid are markers of pregnancy health.

Either your genetic counsellor or perinatologist recommends you the test. In some cases a previous screening test like the first trimester screen, Quad Screen, or triple screen is primary. When the results are not satisfactory from the non-invasive screening test, you can negotiate amniocentesis. An alternative test for amniocentesis is Chorionic Villus Sampling.

Amnio tells you about hereditary disorders like spina bifida, Downs Syndrome and cystic fibrosis. You can also evaluate baby’s lung functioning, infections and premature birth risk by amniocentesis in the third trimester. That’s called fetal lung maturity amniocentesis.

What conditions does amniocentesis test for?

While amnio mainly detects genetic disorders, it can also test fetal lung functioning. Amniocentesis at 32 weeks examines lung functioning of the baby to decide whether the baby is ready for coming out. Before inducing labor, amnio is a way to determine whether its safe.

A condition called Rh sensitization kills fetus using the mother’s immune system. Blood factors of mother and baby conflict and immune cells from the mother’s body destroy the baby as a foreign entity.

Other infections can also be detected during amnio testing based on the factors obtained in the fluid. At times excess fluid accumulates in the sac choking the baby. Though the reason is different the procedure for removal of excess liquid is the same.

What disorders and defects can amniocentesis detect?

Amnio test looks mainly for the genetic disorder in the baby. The results are accurate and are clear yes or no answers. Depending on maternal age and other factors gynecologists recommend the test. Complications such as Tay Sachs, Muscular Dystrophy, Cystic Fibrosis, Downs Syndrome and Sickle Cell Disease are life-threatening. Early detection allows time for thinking and taking the right decision.

Groups of women who are above 35 years, with abnormal screening results and history of pregnancy complications must get the test. Before the stage of getting an amniocentesis, you do have an ultrasound and optional screening.

Even while getting the amniocentesis while drawing out the fluid you have an ultrasound. At the stage where you get the test, defects such as clubbed digits, heart anomalies, and cleft palate also appear.

Lung functioning and the risk of premature delivery are other things third-trimester amniocentesis tells. Gender determination is extremely accurate with the test. However, sex determination using amniocentesis is illegal in some countries like India.

Anencephaly and open neural tube defects also show up during amnio testing. Both involve the incomplete development of the brain and spinal cord.

What chromosomal abnormalities can amniocentesis detect?

1) Trisomy 21 Downs Syndrome

Trisomy means an extra copy of the chromosome, making it a triplet instead of a pair. Bringing in the imbalance in genetic composition, trisomy 21, causes developmental delays. The child does survive but can have heart diseases, tongue displacement, thick skin, intellectual disabilities and speech delay. Treatment options other than supportive therapies like shelter care and special activities are not fully understood.

2) Trisomy 18 Edward’s Syndrome

Fatal genetic disorder Edward syndrome symptoms include clenched hands, defects in organs and a small head. Sex organs may also be absent partially or wholly. A hernia, kidney dysfunction, breathing difficulties, drooping eyelids and low set ears are other signs. Babies with trisomy 18 generally die within their first year.

3) Turner Syndrome one x absent

Females are affected by the disorder where the supposed sex chromosome pair has a singleton. One copy of the X chromosome either disappears entirely or partly. Women with Turner syndrome have a delay in puberty and are short. Congenital heart disease is also common in such patients. Celiac disease, amenorrhoea, and Thyroid diseases are co-occurring disorders.

4) Klinefelter Syndrome extra x present

Only male children can have Klinefelter syndrome. They have an extra copy of X chromosome which imparts feminine bodily features. The crotch doesn’t develop properly, and breast formation occurs. Production of sperms is absent, infertility, limp muscles, lack of libido, osteoporosis, and ADHD are other symptoms of the disorder.

5) Trisomy 13 Patau Syndrome

Only advanced labs conduct the test for trisomy 13 2. Babies born with the syndrome have intestines outside the body, small head, and severe body deformation. They have intellectual disabilities, low birth weight, seizures, and heart murmuring. Majority of such cases lead to infant mortality.

What Gene Related Genetic Diseases can amniocentesis detect?

Other than chromosomal defects, genetic diseases occur due to a single gene defect. Marfan syndrome, Ehlers Danlos Syndrome, Lejeune’s syndrome, Prader Willi syndrome 3 and many others are because of mutation. Amniocentesis can detect some of them.

For instance, the Marfan syndrome involves a defect in the fibrillin gene that affects connective tissues. Individuals have a long stature and limp joints of limbs leading to hypermobility. There is a tendency to develop heart diseases and lens dislocation.

Blood Disorders That Amniocentesis can Detect

1) Sickle Cell Anaemia

Blood has red blood cells that have hemoglobin to carry oxygen. When there is a mutation (change) in the hemoglobin structure, the cells get a peculiar sickle shape. Oxygen transport is affected, and the person is not able to perform strenuous exercises. Spleen, brain, and capillaries clog due to these weird cells, and the anemic condition persists.

2) Thalassemia

There are different types of Thalassemia alpha, beta, and delta. Hemoglobin production is defective and lowered. When the mutation is 3/4, there is jaundice, bone malformation and enlargement of spleen and liver. Complete mutation results in stillbirth or death after delivery.

3) Hemophilia

Bleeder’s disease is due to the absence of antihemophilic factor that clots blood. Blood transfusion is the only cure for temporary control of symptoms.

4) Fragile X Syndrome

Related to sex chromosome the disease involves symptoms related to neural and behavioral abnormalities.

5) Cystic Fibrosis

Accumulation of mucus inside different organs causes blockage of pathways. Cysts appear in pancreas due to an abnormal protein formation. Baby tastes salty when you kiss him. That is because the salt balance of the body is not maintained. There is 1:1800 risk factor in North Americans and Caucasian Europeans.

Some inheritance probability can be done using a pedigree analysis such as color blindness. You can decide whether you would want to take a confirmatory amnio or rely on the pedigree.

Amniocentesis involves a second-trimester scan that shows neural tube defects.

Sex Determination Using Amniocentesis

The karyotype of fetal cells from the amniotic fluid tells about the sex of the baby. Just like testing for other disorders amnio can be used for looking for the sex chromosomes of the baby. It’s the most accurate method for determining sex.

By the 16th week, a gender prediction ultrasound is also quite accurate. Babies playing with their umbilical cord presents a false image. Amniocentesis can also go wrong but rarely.

Who all should get amniocentesis? And who must not?

Those who feel that amniocentesis results can affect their willingness to have the baby must get the test.

Those who must get the test include:

  1. Women with pedigree analysis or family history of a particular genetic disease
  2. Who has had a positive screening result
  3. Are above 35 years
  4. Have partners with a history of genetic disorders or carriers of the disorder genes
  5. Previous pregnancy ended in miscarriage or abnormal infant
  6. An ultrasound scan showed abnormal findings

Women who have Rh incompatibility with their baby shouldn’t take the test. As the antibodies will move in the sac from the puncture. Similarly, women with HIV or hepatitis can’t get an amniocentesis or invasive tests. The virus moves inside the amniotic sac during the procedure of the test.

When should you take amniocentesis?

Amniocentesis is ideally between 15-20th week. There is third-trimester amniocentesis for other reasons. Determining the labor dynamics is the purpose of taking amnio in 32 weeks.

What happens during amniocentesis?

The needle needs to prick at right spot, and so nothing should hinder ultrasound observation. Before 20 weeks your uterus isn’t large enough for showing through clearly. Thus your bladder needs to be full stretch out.

Drinking a lot of water is essential in amniocentesis before 20 weeks. After 20 weeks pregnant, you can get the test without taking any water or special eating precaution. A full bladder can cause an injury in amnio 20 weeks.

During the test, your doctor will use a gel to guide the transducer for locating the baby. No anesthetic is used during the examination. A mild prick feels in the abdomen just like getting an injection. Cleaning using an antiseptic ensures that no external pathogen goes inside.

Gradually your doctor will push in the needle in your stomach. When the needle pokes in your uterus, you’ll feel some cramps.

After withdrawing the fluid, the needle is pulled back. Keep breathing deeply and say some affirmations to distract yourself.

Once the needle is out your doctor will continue with the ultrasound to monitor your baby. Looking for neural tube defects, heartbeat, and size of your baby the doctor will glide transducer around. You can feel stinging near the spot where the needle was put.

The fluid sample goes to the lab where the cells are cultured and multiplied. Various tests are done for diagnosis. Reports take time because of the larger number of tests.

Risks associated with amniocentesis

  1. Miscarriage
  2. Rh sensitization or transmission of infections 4
  3. Amniotic fluid leaking
  4. Needle injury
  5. Infections in the uterus

When to call the doctor after amniocentesis?

Your results will be available by the end of 3 weeks. However, in case you’ve severe cramps or discomfort call your doctor. Can I resume activity after amniocentesis? One can start her daily routine soon after the test. Pausing sexual activity and workout for a day or two would be a good choice. Acetaminophen is safe for the discomfort that remains after the amnio.

In case you get fever or inflammation, contact your OB soon. Another important thing is to keep track of is fetal movements. No fetal movement after amniocentesis even upon stimulation is an emergency.

Women who have a risk of miscarriage must report if their uterine cramps don’t go after the procedure.

After getting Amniocentesis Results

Normal results

You can wait for the third trimester to get another amniocentesis if you’re at high risk. There is a rare chance that a genetic disease develops after this. Only upon exposure to radiation or another agent will there be a risk of genetic mutations. Fetal lung function test can be done in the third trimester. Otherwise, it is time to relax and enjoy the rest of your pregnancy while taking care.

Abnormal amniocentesis Results

We can understand the anxiety and despair the result brings to a woman who has been carrying a baby since 3-4 months. Midway you are hit by the shocking news. Nonetheless, you should appreciate the fact that you have a body that can create life. Considering the facts over emotional dilemma, taking the right step is crucial for your and baby’s life.

How accurate is amniocentesis?

It’s one of the most accurate methods of detecting genetic diseases and sex of the baby. The accuracy rate of amniocentesis is 99 out of every 100 women who opt for the test. Even with risks such as needle injury, leaking amniotic fluid and Miscarriage, amnio is immensely useful.

Footnotes

  1. https://www.stanfordchildrens.org/en/topic/default?id=amniocentesis-procedure-92-P07762
  2. https://ghr.nlm.nih.gov/condition/trisomy-13
  3. https://www.pwsausa.org/
  4. https://www.nhs.uk/conditions/amniocentesis/risks/