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First Trimester Screening - Why Is It Necessary?

Written and reviewed by
Dr. Sumati Saxena 90% (21 ratings)
MBBS, MS - Obstetrics and Gynaecology
Gynaecologist, Allahabad  •  34 years experience
First Trimester Screening - Why Is It Necessary?

A healthy pregnancy is one where the mother and the child both enjoys good physical and mental health. While all parents wish their child to be in the pink of health, incidences of birth-defects are on the rise. This makes the screening tests, especially during the first trimester, very important. These tests play a significant role in determining the well-being of a pregnant woman and also in the diagnosis of any abnormalities, especially chromosomal or genetic aberrations that can give rise to a host of problems including Trisomy 18 or Down Syndrome in the baby. In this article, we will discuss some of the first-trimester screening tests and their significance.

The screening tests involve a series of blood tests (maternal blood) and ultrasound scans to monitor the movement and development of the fetus.

  1. Maternal blood tests: The proteins PAPP-A (pregnancy-associated plasma protein A) and Free ß-HCG (free-beta human chorionic gonadotropin protein) are produced during the early stages of pregnancy by the placenta. These proteins play a pivotal role in ensuring the well being of the fetus and should ideally be present in a slightly elevated level. A maternal blood test showing a low concentration of PAPP-A and free ß-HCG is often indicative of chromosomal abnormalities or genetic defects in the baby.
  2. Nuchal translucency screening test: A characteristic symptom of Down Syndrome is an increased thickness, especially at the back of the neck. In Nuchal translucency screening (during the first trimester), an ultrasound of the back of the fetal neck is done to check its thickness and also to look for any unwanted accumulation of fluids, both of which contributes significantly in the diagnosis of Down Syndrome.
  3. In some incidences, there may be a combined first-trimester screening (an amalgamation of Nuchal translucency screening and maternal blood tests). The probability of the baby suffering from the chromosomal aberrations such as Down Syndrome, Trisomy 13, can be more precisely determined by the combined screening.

In case the individual or the combined screening tests indicate some abnormalities, few other tests may be carried out such as

  1. Amniocentesis: The test involves collecting a sample of the amniotic fluid (the fluid present inside the amniotic sac and acts as a protective shield for the fetus ensuring healthy fetal development) and examining the cells present in it for chromosomal defects (number as well as structure). Amniocentesis is normally carried out between the 15th-20th week of pregnancy.
  2. Chorionic Villus Sampling: Like Amniocentesis, Chorionic Villus Sampling is also a prenatal diagnostic test that plays an instrumental role in the evaluation of the fetal karyotype that goes a long way in the diagnosis of chromosomal and genetic disorders.

Benefits of First-trimester Screening
The screening tests during the first-trimester comes as a blessing, especially under the following situations

  1. Either of the partners is a carrier of the Down-syndrome (or similar genetic disorder) gene.
  2. You already have a child with a genetic or chromosomal disorder.
  3. Women having a late pregnancy (35 years or more).
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