If you’re over 35 or at risk for having a baby with a birth defect, your obstetrician or healthcare provider may recommend that you have a prenatal diagnostic test called an amniocentesis. There are risks that come with an amniocentesis that you should be aware of, so you need to do your research before deciding whether to consent to this second trimester prenatal test.
What is an Amniocentesis?
An amniocentesis is a diagnostic test that looks for certain birth defects and genetic problems in your unborn baby. Amniocentesis is usually performed between 15 and 20 weeks of pregnancy. (There is also an earlier diagnostic test called a CVS – Chorionic Villus Sampling – that can be performed late in the first trimester.)
During an amniocentesis test, your doctor will withdraw a small amount of amniotic fluid, which surrounds your unborn baby. Because amniotic fluid contains live fetal cells (that are shed from your baby) and chemicals produced by your baby, like alpha-fetoprotein (AFP), an amniocentesis can provide your doctor with vital information about your baby’s health.
Why Have an Amniocentesis?
There are many reasons why a woman may choose to have an amniocentesis. You may want to have an amnio if you’re risk for certain birth defects. For example, you may have a family history of specific birth defects and you want to find out your baby’s health. All women over age 35 are at higher risk for genetic defects, so they will be offered an amniocentesis. You will also be offered an amnio if you had an abnormal ultrasound.
Because an amniocentesis’ provides you with vital information, the results may affect your decision to continue the pregnancy, or it may arm you with the knowledge of preparing to have a special needs child.
Although an amniocentesis cannot detect all birth defects, it can accurately confirm that your developing baby has certain health problems. An amniocentesis can detect nearly all chromosomal disorders, including Down syndrome, trisomy 18, trisomy 13, and all sex chromosomal abnormalities. This diagnostic test can also diagnose hundreds of genetic problems – like Tay-Sachs disease, sickle cell disease, muscular dystrophy, and cystic fibrosis. Neural tube defects, like spina bifida and anencephaly, can also be detected with an amniocentesis.
If you’re having an amniocentesis, you can also ask the doctor about your baby’s sex. Amniocentesis is the most accurate way to determine your developing baby’s gender. (Ultrasounds are accurate, but not as accurate as an amniocentesis.)
There are certain problems that an amniocentesis cannot diagnose. This includes physical birth defects, like heart malformations, cleft palate and cleft lip. These birth defects can be picked up, however, in a second trimester ultrasound.
Other reasons why you may need an amniocentesis include:
- To check the maturity of your baby’s lungs, if you need to have an early delivery due to medical reasons. This type of amniocentesis is performed in the third trimester.
- To diagnose a uterine infection.
- To check on your baby’s health if you have a different Rh factor than your baby.
- To decrease the volume of amniotic fluid in the womb.
Accuracy of an Amniocentesis
An amniocentesis is pretty accurate when it comes to diagnosis genetic problems. Experts estimate the accuracy of an amniocentesis is 99 percent. Sometimes, an amnio will need to be repeated due to technical problems – such as not enough amniotic fluid was collected, or the collected cells failed to grow in the lab.
What Happens During an Amniocentesis
When you come in for your amniocentesis, you will be asked to lie on an examining table. Next, the doctor will clean your belly with alcohol or another antiseptic. An ultrasound will be used to figure out exactly where to insert the needle – where is the safest area to collect fluid.
Then, under ultrasound guidance, your healthcare provider will insert a long, hollow needle through your abdominal wall, into the amniotic sac, and withdraw a small amount of amniotic fluid. After the amniotic fluid is collected, the needle will be withdrawn.
During the amniocentesis procedure, you may experience some cramping and pressure. (Some women experience no discomfort at all.) Before the procedure, your doctor may offer to give you a local anesthetic to numb your abdomen.
If you have Rh-negative blood, your doctor will give you a shot of Rh immune globulin to prevent Rh sensitization.
In the two to three days following your amniocentesis, you should take it easy. Avoid having sexual intercourse, traveling by pain, or any heavy lifting. You may notice some minor cramping. But if you have painful cramping, vaginal bleeding, or you start to leak amniotic fluid, contact your healthcare provider immediately. These could be signs of a possible miscarriage.
The decision to have an amniocentesis is yours, but you need to understand the risks that come with it.
An amniocentesis is considered a very safe procedure, and over 200,000 amnios are performed annually. Because an amniocentesis is an invasive procedure, it does come with a number of risks.
- Miscarriage – The primary risk that comes with having an amniocentesis is having a second trimester miscarriage. Although it’s a slight risk, it’s one that you may not want to take. Research estimates that your miscarriage risk is between 1 in 300 to 1 in 500. Your miscarriage risk is higher when an amniocentesis is performed before 15 weeks.
- Uterine Infection – In rare cases, having an amniocentesis can lead to a uterine infection.
- Cramping and Spotting – After having an amniocentesis, some women experience abdominal cramping and some spotting (light vaginal bleeding).
- Needle Injury – During an amniocentesis, your developing baby might move his or her arm or leg into the path of the needle. Serious injuries are rare, but they do happen.
- Leaking Amniotic Fluid – Another rare complication from an amniocentesis is the leakage of amniotic fluid through your vagina.
- Rh sensitization – In rare circumstances, the baby’s blood can enter the mother’s bloodstream. If the mother has Rh-negative blood and the baby has Rh-positive blood, this can cause a complication called Rh sensitization.
If you are worried about any cramping, leaking of amniotic fluids, or any other worrisome symptoms after an amniocentesis, consult your obstetrician or healthcare provider right away.
Amniocentesis and Miscarriage
Miscarriage after an amniocentesis is one of the most worrisome risks.
After an amniocentesis, the risk of miscarriage is low (1 in 300 to 500). Keep in mind that some women end up having second trimester miscarriages anyway, so it’s hard to know whether the miscarriage was caused by the amniocentesis or from another factor.
Before consenting to an amniocentesis, you should weigh the risk versus the benefit of knowing whether or not your baby has a genetic or birth defect.
To lower your miscarriage risk, you need to find a doctor with many years of experience doing amniocentesis. You should also ask beforehand about continuous ultrasound guidance during the amnio. This will improve the chance that your doctor extracts enough amniotic fluid during the first try. Plus, with continuous ultrasound guidance, injuries from the amnio needle are rare.
When Will You Get the Results?
You must be patient after you have the amniocentesis. You will not get the full results for two to three weeks afterwards. During this time, your amniotic fluid sample will be sent to a lab, where the scientists will measure the amount of alpha-fetoprotein (AFP) in the amniotic fluid. The baby’s living cells, found in the amniotic fluid, will be cultured and checked for any evidence of genetic birth defects and chromosomal abnormalities.