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| Explanation of amniocentesis . |
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Many women undergo the agonizing decision of whether or not to have an amniocentesis in pregnancy. An amniocentesis is when your doctor uses a long, small caliber needle to go through the abdomen, into the uterus, through the bag of water and into the amniotic fluid around the baby. Amniotic fluid, about 20 cc, is then abstracted and tested for various reasons. Ideally the needle never goes near the baby, however sometimes babies kick, and this is rarely known to harm the fetus. In fact, your doctor will be very careful to avoid areas of fluid near the face, eyes, and heart for this reason. In general, harm to the fetus is not considered to be one of the major amniocentesis risks. This is just extrememly uncommon.
Multiple tests can be run on amniotic fluid:
· A fetal karyotype, or gross examination of chromosomes to exclude conditions such as Down Syndrome. This test lines up the chromosomes and counts them. This makes sure you have the right number of books.
· Pinpoint genetic mutation test. For instance, if both mom and dad carry a cystic fibrosis mutation, we can see if the fetus inherited both mutations, and will therefore have cystic fibrosis; making sure there are no typos in the books.
· Viral studies on the fluid to see if the fetus has been infected by viruses that are teratogenic (birth defect causing) like CMV, and toxoplasmosis.
No one is ever told they must have an amniocentesis. However, there are many situations when, given the concern of chromosome disorders, it is suggested. Such situations are:
· Advanced maternal age, over 35, with maternal desire to have definitive testing for chromosome abnormalities. (see www.AskAnOB.com/toppregnancyquestions )
· Abnormal Down syndrome screening, such as alpha fetoprotein or AFP, quad screen or nuchal translucency. (see www.AskAnOB.com/nuchaltranslucency )
· Abnormal second trimester genetic ultrasound suggesting possibility of chromosome abnormality. (see www.AskAnOB.com/downsyndromescreening )
· Prior child affected by a major chromosome disorder.
· Known genetic mutations the fetus is at risk for (for instance, sickle cell anemia or cystic fibrosis).
Unfortunately, there are risks of pregnancy loss. The most common complications are rupture of the bag of water, labor, infection and bleeding. Fetal injury rarely occurs. When one of these complications occurs, most often the pregnancy will be lost within several days of the procedure. In some cases, however, the bag of water can reseal. Obsetricians and Perinatologists performing undergo special training to be permitted to do such procedures.
The loss rate for the pregnancy has traditionally been quoted to be approximately 1: 200 procedures. More recent data, however suggest the risk of amniocentesis is actually substantially lower in the modern era of ultrasound and using modern techniques. Two recent trials have substantiate this claim. The FASTER trial was a large study of over 35,000 women that suggested the pregnancy loss rate of baseline loss rate was actually more like 1: 1600 or 0.06%. In another recent publication by Odibo, they determined in over 51,000 procedures they loss about 1: 769. This again is far less than traditionally quoted loss rates, and should be reassuring to patients contemplating such procedures.
When a patient is contemplating amniocentesis, risks and benefits must be considered. Amniocentesis is definitive, it states "yes" or "no" to whether the baby has Down Syndrome, unlike nuchal translucency testing, alpha fetoprotein (triple or quad) screening, and ultrasound for anatomy. Of course, this is very important. Many times women want the option of pregnancy termination, and therefore must know for sure if the fetus is affected. Other times, they may not be considering termination of the pregnancy, but simply want to stop worrying or know for sure to prepare. A mathematical benefit to amniocentesis in that setting cannot be assessed, but is very real.
Amniocentesis also places the pregnancy at some risk, and hundreds of pregnancies are lost every year because of invasive testing. This risk is small, as above, but absolutely needs to be considered heavily prior to proceeding forth with invasive testing.
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