First Trimester Screening

About the Screening

First trimester screening is a prenatal screening test that provides vital information regarding the risk of  fetal chromosomal defects like Down syndrome. An ultrasound is done to measure the size of the gap at the back of the neck of the baby (nuchal translucency) and blood test done to measure two pregnancy related chemicals in the mother’s blood namely pregnancy associated plasma protein A and human chorionic gonadotrophin. This test is usually done between 11 and 14 weeks of pregnancy but first trimester screening may be done at about 9 weeks.

First trimester testing should be considered as necessary although it is largely optional. Based upon the results of the ultrasound, blood tests and the mother’s medical and family history, the doctor determines the risk of genetic defects in the baby. Patients with low risk level are more likely to have a healthy pregnancy and have a healthy baby. Sometimes if the risk level comes out as moderate or high the doctor may recommend other confirmatory tests.

Importance of Screening

First trimester screening is done to evaluate the risk of carrying chromosomal abnormality like Down syndrome and Edward syndrome. Down syndrome results in mental and social impairment along with a number of other associated organ defects. Edward syndrome is another common chromosomal abnormality characterized by defect in different organs particularly the heart and kidney.

Neural tube defects like spina bifida are not diagnosed by first trimester screening test since it is done in early pregnancy. The result of these tests helps to make decisions regarding undergoing other confirmatory tests, medical treatment required and the course of the pregnancy. The first trimester screening test is optional and this test only shows the risk of the baby of suffering from genetic diseases like Down syndrome. It does not confirm the presence of the abovementioned genetic diseases.

Before undergoing the test the patient should consider the impact of the result. It may alter the way in which the pregnancy is managed and may prompt the parents to make difficult decisions about whether to continue with the pregnancy in some cases.

Testing Procedures

No special preparations are required prior to undergoing the test and the mother can eat and drink as normal. The screening includes a blood test along with ultrasound examination. Blood is collected usually from the upper arm  and is sent to the laboratory for testing. During the ultrasound examination the doctor or the technician inserts the ultrasound probe through the vagina or places it on the lower abdomen. The waves produce an image that allows for the correct measurement of the clear space at the baby’s neck.

First trimester screening test does not carry any risk apart from mild discomfort during the drawing of blood. Depending upon the age of the mother, ultrasound report, blood test reports, family history of genetic disease and mother’s medical history, the doctor determines the risk of genetic disease in the unborn baby. The test result is given as positive, negative or as probable. Positive test results are confirmed by other confirmatory test like chorionic villous sampling, non-invasive prenatal testing and amniocentesis.

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