Detection of autosomal trisomies in second trimester of pregnancy

Trisomy is a type of polysomy.
In which instead of normal two instances, three instances of particular chromosome can be seen.
 The trisomies that can commonly affect the intrauterine fetus are
trisomy 21 ( Down syndrome), trisomy 18 (Edwards syndrome),
 trisomy 13 Patau syndrome.
The chances of having babies with trisomies increases with maternal age.
The possible risk of these trisomies can be detected during pregnancy by screening tests.
In second trimester:
-Quadruple test:
It is a blood test.
It should be done between 16 to 22 weeks.
In which levels of
AFP (Alfa feto protein)
hCG (Human chorionic gonadotropin)
uE3 (unconjugated estradiol)
Inhibin A are analyzed.

High HCG, inhibin A levels, low AFP and uE3 levels indicate high risk for trisomies especially Down syndrome.
Triple test measures first three and Inhibin A is not included in it.

Amniocentesis:
It is a invasive test and can be used as a diagnostic test.
Can be performed between 16 to 21 weeks.
By this amniotic fluid is collected and possible fetal cells in it are analyzed for chromosomal abnormalities.
It is having little bit higher risk for miscarriage and infections.

TIFFA scan (Targeted imaging for fetal anomalies):
It is a ultrasound examination to detect fetal anomalies.

It should be performed between 18 to 22 weeks.

By combined result of all these investigations one conclusion can be drawn regarding the possibility of trisomies.


Detection of autosomal trisomies in first trimester:
detection-of-autosomal-trisomies-in first trimester

Detection of autosomal trisomies in first trimester of pregnancy

Trisomy is a type of polysomy.
 In which instead of normal two instances, three instances of particular chromosome can be seen.
 The trisomies that can commonly affect the intrauterine fetus are
trisomy 21 ( Down syndrome),
trisomy 18 (Edwards syndrome),
trisomy 13 Patau syndrome.
The chances of having babies with trisomies increases with maternal age.

The possible risk of these trisomies can be detected during pregnancy by screening tests.
In first trimester:
-Double marker test is a blood test which is used to identify the risk of chromosomal abnormalities like trisomies.
It identifies levels of
hCG(human chorionic gonadotropin),
PAPP-A(pregnancy associated placental protein - A) in maternal blood.
In case of possible abnormality, the levels of these substances will be high.
The cutoff values may differ from lab to lab.

-Nuchal Thickness in the ultrasound. Increased nuchal thickness indicates high risk for Down syndrome.

At around 11 to 13 weeks, nuchal thickness less than 3.5 mm can be considered as within normal limits.
 To come to one conclusion combined result of blood test and nuchal thickness should be considered.

Diagnostic tests can give a clear picture.
In first trimester the diagnostic tests that can be performed are:
-CVS (chorionic villi aspiration sampling):
It can be performed between 10 to 13 weeks of gestation.
By this fetal tissue can be obtained and genetically analyzed.
It is true that chorionic villi aspiration sampling is a better test but it is having risks like chances of miscarriage, infection etc.
And it is difficult to perform in situations like low lying placenta.

-Non invasive tests like NIFTY(Non invasive fetal trisomy test).
It is a blood test.
In which maternal blood in drawn and available fetal cells in it are analyzed for chromosomal abnormalities.
As it is a non invasive test, so there is low risk for miscarriage and infection.
It is more useful in situations like low lying placenta.
According to the studies available NIFTY is also having good accuracy in detecting the abnormalities.


Detection of autosomal trisomies in second trimester:
http://srsree.blogspot.com/2014/03/detection-of-autosomal-trisomies-in_13.html