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Prenatal Screening Overview

Prenatal chromosomal screening is a safe and a simple screening test you can take as a pregnant mother. These screening tests can ensure that your pregnancy is safe and also assess the probable risk of any chromosomal conditions of your baby in the womb.

  • These tests are recommended by Gynaecologist across the world for all pregnant women
  • Prenatal Screening is the most important test to assess your baby’s health in the womb
  • They are mostly performed during the first and second trimester of the gestational period
  • It only requires a small amount of maternal blood for the screening process and hence safe
  • The tests enable the to-be parents to make informed decisions on continuance of pregnancy

Why Prenatal Screening?

The objective of prenatal screening is to screen health problems that could affect the pregnant mother and the baby inside the womb. It allows the gynaecologist and the expectant parent to get enough information and have a fully informed decision about pregnancy continuation and management. Prenatal Screening is recommended for all pregnant women.

Prenatal screening tests are useful in the following ways:

  • Prenatal screening is a safe way to check for chromosomal conditions & hence globally recommended all pregnant women.
  • These tests reassure expectant parents when the test results are normal and also highlights on the probable risk in their baby.
  • These comprehensive screening protocol ensuring necessary medical care and support during pre & post pregnancy.
  • It helps the pregnant couple to prepare and make an informed decision; based on further confirmatory diagnostic tests.

Factoids on Prenatal Screening

India ranks the highest in the world with an annual estimate of 1.3 lakh babies born with chromosomal disorders

Currently, the incidence of Down syndrome in India is 1:800, which means over 32,000 babies are born every year

American college of Obstetricians & Gynaecologists (ACOG) suggests prenatal screening to all pregnant women

Society of Obstetricians and gynaecologists of Canada (SOGC) recommends prenatal screening for clinically significant chromosomal conditions

When is PNS done?

Prenatal Screening test is usually recommended for pregnant women from the first trimester of pregnancy to check the baby’s normal growth and development.

  • In the first trimester biochemical screening tests can be done between 9 weeks and 13 weeks and can stretch for another 6 days too
  • Nuchal translucency (NT) ultrasound test is performed between 11 and 13 weeks of pregnancy to check for neural tube defects
  • If the to-be mother misses her 1st trimester biochemical screening, she can opt for a triple or a quadruple marker in the 2nd trimester (15-20 weeks)
Disorders Screened

Usually, humans have 46 chromosomes arranged in 23 pairs; each pair comprises of one chromosome from the mother and one from the father. Changes in the chromosome number or structure may cause chromosomal conditions in babies.

General Chromosomal Abnormalities:

  • Chromosomal conditions in the foetus may result in miscarriage, still-birth or developmental problems or complications in babies
  • About half of miscarriages are caused by chromosomal abnormalities and the baby may not survive beyond 20 weeks in the womb
  • Children born with chromosomal conditions show various symptoms like intellectual disabilities & developmental defects
  • Sometimes the symptoms manifested in the children with such abnormalities may vary based on the affected chromosomes
Commonly Screened Disorders

Down Syndrome (Trisomy 21)

  • Down syndrome in humans caused by the third copy of the 21st chromosome one of the most common chromosomal abnormality
  • It causes intellectual disabilities, developmental delays, short limbs, heart conditions and distinct facial features such as mongoloid representation
  • The risk increases if the previous pregnancy is affected with Down syndrome; when the age of the mother is above 35 and family history

Edwards and Patau Syndrome (Trisomy 18 & 13)

  • These are the second most common chromosomal abnormalities caused by an extra copy  of the chromosomes 18 & 13
  • The risk of a baby being born with such conditions is 1 in 2500 pregnancies, Patau syndrome affects 1 in 8000-12,000 births
  • Babies born with Edwards or Patau syndrome may experience congenital heart disease, brain abnormalities & growth problems
  • Children affected with these conditions may also possess abnormal facial structures, severe birth defects and health problems
  • Mostly, these chromosomal conditions result in miscarriage or still-birth and hence the chances of survival are less

Other Common Chromosomal Conditions

  • These are caused by duplications or deletions of the chromosomes or parts of a chromosome, resulting in Klinefelter Syndrome, Turner’s Syndrome & Triple X syndrome
  • Some chromosomal conditions occur when a segment of chromosome is deleted or duplicated; this also causes birth defects and developmental issues in babies

Open Neural Tube Defects (ONTDs)

  • Neural tube defects are birth defects of the brain or spinal cord that occurs during the 1st month of pregnancy
  • Neural tube defects are birth defects that occur when the brain or the spinal cord does not form properly in the baby
  • During developmental phase, if the neural tube does not close completely, it forms open neural tube defect in the baby
  • If the neural tube defect involves spinal cord, it is called spina bifida and if it is associated with the brain, it is called anencephaly
  • Babies born with spina bifida have difficulty in walking, no control over bowel and may also experience mental disabilities
  • Babies born with anencephaly die soon after birth or stillborn, since their brain development is highly limited to survive
Guidance and Counselling

All Pregnant women who undergo diagnostic testing should undergo Prenatal genetic counselling. BabyShield offers medical guidance and support to mothers through trained counsellors or through your gynaecologists. If the screening test results are positive, it is essential to let the expectant mother know the following:

Positive Screening Shows

Positive screening does not mean that the baby is affected by a chromosomal condition. There are chances of false positives too so it is better to confirm through next level diagnostic tests

Confirmatory Tests

The detection of chromosomal condition is further investigated using the parents’ chromosomes previous pregnancies and family history before making a firm diagnosis

Decision Making

The pregnant mother has the option of continuing or terminating the pregnancy. If the mother chooses to continue, a foetal echocardiogram with routine obstetrical care are provided

Ray of Hope

Various support services are available for kids with down syndrome, they can attend school, grow older, hold jobs, live independently & also make lasting contributions to the society