First trimester screening

First trimester screening refers to the prenatal screening test, which helps in early detection of an abnormality in the unborn fetus. Some of the abnormalities, which can emerge in an unborn fetus are genetic or chromosomal disorders like Down’s Syndrome (trisomy 21) and Edwards Syndrome (trisomy 18). The screening also helps to understand the profile of the growing baby. The First trimester screening test includes the following steps:

  1. Blood test – It is done to evaluate the Human chorionic gonadotropin (hCG) and Pregnancy-associated Plasma Protein-A (PAPP-A), which are pregnancy- determined substances, in the expectant woman’s blood
  2. Ultrasound scan – It is done to examine the amount of clear space or area in the tissue located at the back of the neck of the fetus (nuchal translucency). In addition, a full pelvic scanning is also done.

First trimester screening test is advised between 11th and 14th week of pregnancy. By assessing the age of the expectant woman and the results of both the blood test and ultrasound scan, the doctor can diagnose if the unborn fetus has any chromosomal abnormality. This helps the family to decide on whether to continue with the pregnancy or terminate it.

If the risk level investigated is low, this screening test can provide early comfort and reassurance of a fit and healthy pregnancy.

If the risk level investigated is moderate to high, then the woman might go for some other definitive tests.


Why it's done? What are the risks? How to prepare for the procedure? Expected Results from the Procedure: FAQ Section:

First trimester screening is a very useful test, which helps in providing early diagnosis of chromosomal problems i.e. risk of either Down’s syndrome or Edwards syndrome.

Down's syndrome causes long-term impairment, which is physical, mental and social.  Edwards syndrome affects multiple body parts and it becomes lethal by the age of 1 year. First Trimester Screening test does not detect neural tube disorders like Spina Bifida.

As the first trimester screening test gives the results in an early stage, it gives more time to the family to decide or manage the pregnancy.

There are certain cases, where it is important for the expectant mother to go for the first trimester screening test. Some of these scenarios are mentioned below.

  • Any family history of conditions highlighted
  • The mother herself or her partner having any genetic disorders.
  • The age of the women carrying the baby is 35 years or above. At this age of the pregnancy, the woman is considered to be at a higher risk of having a chromosomal disorder like Down’s syndrome or Edwards syndrome.
  • Spontaneous abortions

 There are other screening tests available which are advised in later stages in pregnancy such as Quad Screen (Quadruple marker) test, which is a blood test done during the second trimester (15-20 weeks) of pregnancy to examine any birth defects in the unborn baby such as Down’s syndrome, Edwards syndrome and Spinal Bifida. The quad screenis done to evaluate levels of the following substances in the women's blood:

  • Human chorionic gonadotropin (hCG); a hormone produced by the placenta
  • Alpha-fetoprotein (AFP); a protein produced by the growing baby.
  • Inhibin A; a hormone produced by the placenta
  • Unconjugated Estriol (UE); a hormone produced by baby's liver and placenta

Some doctors may advise a combination of both the tests i.e. First trimester screening and Quad test, in order to get a clear picture. This would enable the physician to make a confirmed and more confident diagnosis on the abnormalities.

Before getting the screening done, the expectant mother should be prepared for the results of the test as negative results can cause emotional stress to the patients.

The first trimester screening test is completely safe and does not have any negative effects on either the mother or the unborn baby. It includes a blood test followed by an ultrasound scan. Both the tests are usually safe. A blood test involves only a pricking of a needle to draw a blood sample from the arm of the expectant mother. An ultrasound scan does not involve exposure to any radiations as in case of CT-scan and X-rays. It is completely safe as it only involves sound waves transmission to capture images. Hence, there is no risk involved in getting a first trimester screening done.

The doctor or the nurse will inform the patient about the details of the first trimester screening test.

Blood test – 

  • The patients is advised to wear half sleeved clothes
  • The clothes should not be tight especially the sleeves part
  • The patient should not panic and should sit calmly.
  • The woman can eat and drink normally before getting g a blood test done.

Ultrasound scanning

  • The woman is advised to wear loose clothes or asked to change into a hospital gown.
  • The woman is asked to avoid wearing any jewelry and stay calm during the procedure
  • The woman can eat and drink normally after the procedure.

During the procedure:

Blood Test

The woman is made to sit in a chair and is asked to relax and calm down. The nurse or the technician will clean the area, from where the sample is to be taken i.e. vein in the arm, with an antiseptic lotion. The needle is inserted into the vein and the blood sample is collected. The needle is taken out slowly and the area is again cleaned with an antiseptic lotion. The patient is asked to press the area where the needle was inserted for a minute or two. The patient is sent for the ultrasound scan.

Ultrasound scanning

The woman is asked to lie down on her back on the examination table. The woman would be asked to remove the lower part of the clothes. The sonographer will insert a thin, slender, wand-like device into the vaginal area of the patient. This wand-like device helps in transmitting sound waves, which get reflected from the vagina and are captured on the monitor to form images. The images are interpreted to examine the amount of clear space or area in the tissue located at the back of the neck of the fetus (nuchal translucency). The ultrasound scanning is a completely safe procedure.

After the procedure:

Blood test

After the blood sample is taken the patient is sent for the ultrasound scan. The blood sample collected is properly labeled with the details of the patient. This sample is then sent to the lab for further analysis. When the sample reports come back from the lab, they are handed over to the doctor. The doctor explains the results of the report to the patient in detail.

Ultrasound scan

The woman is asked to change into normal clothes. The expectant woman can go back home after the ultrasound scanning is done and can resume doing normal routine activities. The images captured are interpreted and the report is handed over to the doctor. The doctor discusses the results of the ultrasound scan in detail with the patient.

The doctor discusses the report of both the blood test and the ultrasound scan in detail with the patient. The age of the expectant woman along with the results of blood test and ultrasound scan are together interpreted and the doctor assesses if it is safe to carry on with the pregnancy and if the baby has any chromosomal abnormality i.e. Down’s syndrome (trisomy 21) and Edwards syndrome (trisomy 18). Any family history of such genetic disorders can also increase the risk of the unborn baby acquiring such diseases.

If both the reports are normal, it means that the mother and the child are healthy and fit and no abnormality is detected.  If the reports are abnormal, it means that the unborn baby might have some abnormality like chromosomal disorders (Down’s syndrome or Edwards syndrome). If the doctor is not certain about the results then some additional tests may be advised to the pregnant woman in order to get a better picture and surety. The first trimester screening gives 85% accuracy in detecting abnormalities in the fetus. In approximately 5% woman, it gives false-positive testing which means that that there is actually no abnormality in the baby but the report says positive. In some cases, the low-risk level cannot guarantee that the baby will be born without any abnormality. Similarly, high- risk levels do not guarantee that the baby will be born with a definitive abnormality.

In case of positive or abnormal test results, the doctor advises secondary testing which may include:

  • Non-invasive pre-natal Testing – This type of testing helps to detect any fetal DNA in the mother’s blood, which can lead to a risk of a chromosomal abnormality in the unborn baby.
  • Amniocentesis - Amniocentesis is a prenatal test done during the 15th week of the pregnancy. Amniocentesis is a procedure where a small sample (less than one ounce) is taken from the amniotic fluid for testing. The volume of the fluid taken depends on the baby’s gestational age.

Chorionic villus sampling (CVS) – It is a test performed in some pregnant women to screen their babies for the diagnosis of any birth defects or pregnancy-related issues. Chorionic villus sampling can also help in early diagnosis of any chromosomal disorders e.g. Down’s syndrome or genetic problems e.g. cystic fibrosis or sickle cell anemia.

Q1. When can the expectant mother start doing normal activities after the screening?
A1. The patient is usually advised to go home and rest. If there are no problems or complications, then the expectant mother can start with the normal routine activities the next day of the procedure. However, the patient is still advised not to perform any strenuous exercises.

Q2. Is it mandatory to go for First Trimester Screening?
A2. No, it is not mandatory to go for this procedure (First trimester screening). The doctor will counsel the expectant mother and explain all the required information about the test and the results (if positive) before the procedure. Hence, it is the choice of the mother whether to opt for first trimester screening test or not.

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