11-14 Week Fetal Exam

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Amniocentesis Test

Just what is the amniocentesis test and how it can help us diagnose certain conditions during your pregnancy?

Who should consider prenatal testing and genetic counseling?

You are pregnant and will be 35 years of age or older on your due date.

You are pregnant with an abnormal expanded AFP blood test. (Quad Test)

You have had an ultrasound of your fetus showing a possible birth defect.

You have already had a child or close relative with a birth defect or genetic disease.

You and your partner are carriers of a recessively inherited disease such as Tay-Sachs, sickle cell anemia, cystic fibrosis or thalassemia.

You are a carrier of an X linked disease such as Fragile X, hemophilia or muscular dystrophy.

You and your partner are closely related to each other (such as first cousins).

You have been exposed to medications, X-rays or other agents during your pregnancy that may be harmful to the developing fetus.

To fill out our online assessment form click here

Why have a scan at 11-14 weeks?

Nuchal Translucency:
Currently the most accurate non invasive test for detecting Down syndrome during pregnancy is the measurement of the nuchal translucency with ultrasound between 11-14 weeks of pregnancy. (See First Trimester Screening)

What is the Nuchal Translucency?
The nuchal translucency is a collection of fluid beneath the fetal skin in the region of the fetal neck and is present in all fetuses in early pregnancy. The fluid collection is however increased in many fetuses with Down syndrome and some other chromosomal abnormalities. It is called a "translucency" because on ultrasound it appears as a black space beneath the fetal skin. It is this black space that you will see measured during the ultrasound scan.

If the Nuchal Translucency is increased what happens next? If the nuchal translucency is increased then you will be offered a test called amniocentesis. This test involves removing fluid from around the baby and examining the baby's chromosomes. In some circumstances an urgent report is requested and if sufficient cells are present in the sample the results may be processed as early as 2-3 days using a technique called FISH analyis. The complete analysis (long term culture) takes 7 to 10 days.

How is the Ultrasound Performed?
Most often, the exam can be performed trans-abdominally. If the resolution is poor or the fetus is not in position for an accurate measurement, a vaginal ultrasound may have to be done. With this approach greater detail is obtained of the fetal anatomy.

What happens if the chromosome test (Amniocentesis) is normal?
For patients where there was an increased nuchal translucency and later a normal amniocentesis result, there is still a slight increased risk of a structural abnormality in the baby (6%, compared to the background risk of 2-3%); eg a congenital heart defect. For this reason a detailed ultrasound examination of the fetal anatomy is required and can be done from 18-20 weeks. A specialized exam of the fetal heart (echocardiography) is also performed at 22 weeks. For most patients the anatomy is normal and the pregnancy progresses uneventfully.

What happens to the increased nuchal translucency with advancing pregnancy?
In the majority of patients this disappears and is not visible at the routine 22 week ultrasound. This explains why it is important that the scan be performed around 11-14 weeks. This is a narrow window of opportunity to screen the baby for chromosome abnormalities.

What is the risk of the scan?
A transvaginal and transabdominal ultrasound examination is a safe investigation at all stages of pregnancy.

What else can the 11-14 week ultrasound scan show?
A scan at 11-14 weeks provides an opportunity to assess the anatomy of the baby. At this early stage of pregnancy it is now possible to determine many structural abnormalities previously only visible at 22 weeks. During the examination many parts the fetal anatomy will be pointed out to you. It is also an opportunity to determine the number of babies present and the baby's heart rate.