What is amniocentesis?
Amniocentesis is a procedure where a sample of amniotic sac fluid is taken with a needle. Using an ultrasound it allows the physician to insert a needle safely and not harm the fetus. The obtained amniotic fluid, which contains cells scaled with the baby, still needs to be tested in the laboratory using genetic and biochemical tests.
When it is done?
It needs to be done after the 16th week in the amniocentesis is done in order to analyze chromosomes or DNA. In some centers it can be done a month earlier. If the delivery must be performed ahead of the right delivery date, then amniocentesis can be done before the birth in order to check the maturity of the fetal lung.
Why is it done?
In the first half of the pregnancy, amniocentesis is done if there is suspicion that the baby has an increased risk for a chromosomal abnormality, a genetic disease or cleft neural tube.
Microscope examination of fetal chromosomes can detect abnormalities such as Down’s syndrome (read here). Chromosome analysis will reveal the gender of the child, so if you do not want to find out this information, warn the doctors. (Otherwise, amniocentesis is not done just because of determining the sex of the child.)
The analysis of fetal DNA in the genes can often detect the disease which has been occurring in your family (i.e. cystic fibrosis). The gene is revealed by a complex technique involving the use of specific genetic probes (samples) and markers.
Analysis of amniotic fluid can also detect conditions such as anencephaly and spina bifida. Although amniocentesis can determine the severity of the damage, very high levels of alpha-fetoprotein (AFP), suggest the existence of neural tube cleft defects or other congenital “open wall” (those where the hole is not closed with the skin or other tissues). AFP may be falsely elevated when a little fetal blood enters the amniotic fluid during the procedure. In such cases advanced levels of ultrasound examination that can detect physical changes caused mainly by neural tube cleft is helpful. In 10% to 30% of fetuses with neural tube fissure AFP may be normal, but advanced levels of ultrasound examination in some cases can detect it in 18th to 20th week.
Rating of the maturity of the fetal lung
This is important if you have to give birth prematurely. By examining the amniotic fluid doctors can tell if the fetus’s lungs developed enough to breathe on its own. This test is done in the second half of the pregnancy.
Disease due to Rh factor incompatibility
Causes the antibodies in the mother’s bloodstream to destroy fetal blood cells. Amniocentesis is useful for the assessment of the fetus and the possibility of reducing complications, and it is done in the second half of pregnancy.
What are the risks of amniocentesis?
In America amniocentesis is done about 200,000 times a year and is thought of as a fairly safe practice. The risk of miscarriage after amniocentesis ranges from 1 in 200 to 1 in 400. In practices where an ultrasound is regularly used to guide the needle, the risk is around 1 in 400. (Following the 3rd month of pregnancy about 3 to 4 pregnancies out of 100 will end in miscarriage even when any prenatal test is not applied.)
In rare cases where amniocentesis causes miscarriage, usual cause is an uterus infection, amniotic fluid leak or preterm labor. If amniocentesis is done with the help of ultrasound, fetus getting stung by a needle is a rare occurrence.
After amniocentesis less severe complications occur. These disorders can be uterine contraction, wetting or discomfort around the place of the injection. Be sure to contact your doctor if such interference persist or become strong.
Amniocentesis description can range from “comfortable” to “like a bee sting” and “momentarily painful” (under a local anesthetic or a short needle prick). The uterus wall cannot be made insensitive therefore the sting of the needle will be felt.
How it is done?
The procedure may take place in a doctor’s office or at an outpatient hospital. It takes about 45 minutes, while setting up the needle and getting the sample of the amniotic fluid only takes 5 minutes.
Given that you will have an ultrasound examination before the amniocentesis, you must first drink a few glasses of fluid. Ultrasound examination is previously done to determine if you carry one or more fetuses, assess gestational age, measured by the size of the child and assess the position of the uterus and placenta.
Your tummy will be cleaned with an antiseptic. Then a sterile conduit to assess the safe place to place the needle will be placed on your stomach. At your request, doctors can use a local anesthetic which will be injected near the main sting that will numb the abdomen wall. A hollow and long needle will be placed into the amniotic sac and uterus through the abdomen. Then a minor amniotic fluid sample (about 1 to 2 tablespoons) will be released. If not enough amniotic fluid is not collected at this point, the needle will be taken out and placed into another place. The amniotic fluid will be transparent and slightly yellowish as it is primarily made of fetal urine. The fetus will be observed on the screen to make sure that it is well. After being marked, the samples are sent to a laboratory.
Maya is a blogger and a freelance writer. She loves writing about anything related to parenting, relationship and fashion trends. She’s currently working on a project for Baby Glimpse, one of the leading bonding ultrasound centers in Sydney, and as a result she was inspired to write this article. Besides working, writing and blogging she’s also juggling one 7-year old and one 5-year old.
Earnest Parenting: help for parents thinking about amniocentesis.
Image courtesy of tmat1075 via Creative Commons license, some rights reserved.