With advancing age, the risk of conceiving a child with a genetic abnormality increases. Because of this, older mothers, including those who have had a tubal reversal, have more reasons to consider genetic testing during pregnancy. A tubal reversal is often done in women who had their tubes tied when they were younger in order not to have anymore children.
A chromosomal abnormality like Down syndrome is associated with advancing maternal age. A number of diagnostic tests are currently available which may detect Down syndrome during pregnancy. These include the nuchal translucency ultrasound and Quad marker screening, among others.
What is a Nuchal Translucency Ultrasound?
A nuchal translucency ultrasound is a sonographic prenatal test which can identify a high risk pregnancy during the first trimester. It is performed between the 11th and 14th week of gestation. Aside from Down syndrome, the test can also detect an increased risk for major heart efects and other chromosomal anomalies in the fetus. Because it is performed during the first trimester, compared to the Quad marker test performed during the second trimester, parents are able to know their risk much earlier in the pregnancy.
The test however does not provide a final diagnosis. If a mother is in the high risk category, she is often advised to undergo an amniocentesis or a chorionic villus sampling. These procedures are invasive and entail a small risk for miscarriage. Findings from these two procedures will generally give the parents a definite diagnosis.
How is the Nuchal Translucency Ultrasound performed?
Nuchal translucency ultrasound is performed either by placing an ultrasound probe over the lower abdomen or by gently inserting a thin ultrasound probe into the vagina. Ultrasound will measure the thickness of the fold located at the back of the fetal neck. Other information needed during the test includes the age of the mother, the gestational age of the fetus, and additional bloodwork.
What are the factors that influence the test results?
The following are important factors that influence the findings from the nuchal translucency ultrasound:
- Age of gestation (should be between the 11th and 14th week
- The scan is obtained with the fetus in the sagittal position
- Hyperflexed or extended position of the fetus may affect results
- The fetal image is enlarged to 75 percent within the screen
- The nuchal lucency should be distinguished from the underlying amniotic membrane
Is a history of tubal ligation reversal a risk factor for a chromosomal disorder?
Tubal ligation reversal has absolutely no adverse affect on the fetus. The correlation between a tubal reversal and any chromosomal disorder is strictly due to the fact that most patients who undergo a tubal reversal are older, and that older patients are inherently at increased risk for a chromosomal disorder in the fetus.