What Is An Amniocentesis?
Amniocentesis is a prenatal test that provides information about how your baby is doing in your womb. The information is gathered from testing a sample of the amniotic fluid (hence it is also known as the Amniotic Fluid Test) which is produced in the amniotic sac at about 12 days after conception. The test is usually conducted between the 16th and 22nd week of pregnancy. Mothers who are recommended for this test are typically those with a high risk for genetic disorders and chromosomal abnormalities.
What does amniocentesis detect?
- Almost all chromosomal disorders, including Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome and Klinefelter syndrome). It has proven to have more than 99 percent accuracy in diagnosing these conditions.
- Several genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease. The test can usually determine if your baby is at increased risk for one or more of these disorders.
- Neural tube defects such as Spina bifida and anencephaly, which is done by measuring the level of a substance called alpha-fetoprotein (AFP) in the amniotic fluid.
When will you be recommended for amniocentesis?
- If you have an abnormal ultrasound
- A family history of certain birth defects
- Previously had a child or pregnancy with a birth defect
- Will be 35 or older at the time of delivery
Amniocentesis may also be done for other reasons such as:
- To assess the maturity of your baby's lungs when considering an early delivery for medical reasons (unless it's clear the baby needs to be delivered immediately regardless of lung maturity)
- To diagnose or rule out an intrauterine infection
- To check on the well-being of your baby if you have a blood sensitization, such as Rh sensitization. This is a complex condition that can occur if your blood is a different type than your baby's.
How does the amniocentesis test work?
- During the procedure a very thin needle is inserted into the lower abdomen to draw out a small amount of amniotic fluid (the fluid surrounding a developing fetus) from the uterus.
- An ultrasound is used to guide the needle during the procedure. Most women report an uncomfortable feeling of pressure, a cramping feeling during the procedure (about 30 seconds to one minute).
- This fluid can be tested for:
- Chromosomal abnormalities like Down syndrome, trisomy 18 and trisomy 13. Testing detects over 99% of all chromosome abnormalities.
- Inherited diseases when parents have been shown to be carriers of the specific disease e.g. Tay-Sachs disease, cystic fibrosis and sickle cell disease.
- Open neural tube defects, such as Spina bifida and anencephaly
- After the sample is taken, another ultrasound check is conducted.
- Note: If your blood is Rh-negative, you'll need a shot of Rh immune globulin after amniocentesis unless the baby's father is Rh-negative as well. (Your baby's blood may mix with yours during the procedure and it may not be compatible.)
It is important to know that neither Chorionic villus sampling nor amniocentesis is able to test for birth defects that do not have a known cause. A few examples are autism, cleft lip, non-specific mental retardation and most heart defects.
The risk of miscarriage in amniocentesis
Amniocentesis carries a low risk of miscarriage. According to the American College of Obstetricians and Gynaecologists (ACOG), it is as low as 1 in 300 to 500. This risk is perceived to be even lower if the doctor or center has extensive experience in performing this prenatal test. The College therefore advocates that all pregnant women be offered the option of diagnostic testing (as opposed to just screening) for Down syndrome, trisomy 18 and open neural tube defects.
How can the risk be lowered?
- Look for an experienced doctor to do the testing. Your gynaecologist or healthcare practitioner should be able to help with this. Check his/her track record with respect to the miscarriages that have occurred on account of this procedure.
- Talk to a genetic counsellor about amniocentesis and other forms of prenatal testing. They can provide detailed information about the different genetic tests so that you can make the right choices for you and your baby.
- When you go for the test ask the doctor to guide you through the procedure. This will help you know and be prepared for every step. It also reduces stress and makes you feel more comfortable which can make the procedure easier to go through.
Amniocentesis helps make important decisions about the future. Moreover, if the test detects a problem early it can sometimes be treated while the baby is still in the womb.
Dr. Jorge L. Gomez earned his Medical Degree in 1990 at Central Del Caribe University in Bayamon, Puerto Rico. Following residency in Obstetrics and Gynecology at Bronx-Lebanon Hospital center in the Bronx, NY (1990–1994), he completed additional fellowship training at New York University Medical Center NY, specializing in Maternal Fetal Medicine (1994-1996). After his fellowship in 1996 he joined South Florida Perinatal Medicine. Dr. Gomez is Board certified in OBGYN and Maternal Fetal Medicine. From 2003–2007 He was a reviewer for the American Journal Of Obstetrics and Gynecology.