Chromosonal Abnormalities in Babies: Causes, Signs & Diagnosis

Baby Born With Extra Chromosome or Trisomy – What Does It Mean?

As a mother, you try everything in your capacity to have a healthy pregnancy and a healthy baby. However, there may be times when babies may develop certain health complications in the mother’s womb due to various reasons. And one such complication that a baby may have is an extra chromosome or trisomy. Is it a serious condition and what does it mean? Well, if you have these questions in your mind, then we recommend that you read the following article to understand this condition in a better way.

What Does It Mean If a Baby is Born With an Extra Chromosome?

In most cases, a baby is born with two copies of each chromosome: one copy is inherited from the mother, and the other from the father. However, sometimes a biological glitch during the cell division may happen, and instead of 46, a baby may be born with 47 chromosomes. In scientific terms, this is called ‘trisomy’.

In the majority of such cases, nature takes care of the situation but ‘aborting’ the foetus – i.e. a mother will suffer a natural miscarriage in the first trimester itself. However, if it does not happen, then the baby may be born with an extra chromosome. Trisomy is most commonly observed in chromosome number 21, a condition known as Down syndrome. All babies who are born with this condition may have some degree of mental retardation, but only 10 per cent of babies may have a severe mental condition. Apart from chromosome number 21, trisomy may also be observed in chromosome numbers 13 (Patau syndrome), 18 (Edwards syndrome), 8 (Warkany syndrome) and 9, each of which is marked by a characteristic set of symptoms – both physical and mental. Babies who have trisomy 13 or 18 rarely live more than a few weeks or months.

Causes and Risk Factors of Extra Chromosome in Infants

You may wonder as a mother that what went wrong and why your baby has this abnormality. Here are the reasons that will let you understand why your baby is at risk:

Causes of Trisomy

1. Meiosis Abnormality

Meiosis is a special kind of cell-division which gives rise to eggs in females, and sperms in males. Both the eggs and the sperms have only 23 chromosomes each – one copy of each chromosome. However, if meiosis goes wrong, it can result in an egg or sperm with an extra chromosome, a missing chromosome, or extra pieces of some chromosomes.

2. Mitosis Abnormality

This is the kind of cell division that lets your single-celled embryo develop into a fully functional baby, before you give her birth. Mitosis occurs throughout life – it helps us replenish dead cells from the body. However, if mitosis occuring in a foetus goes wrong at some point, it can lead to trisomy.

Mitosis versus Meiosis

Risk Factors of Trisomy

1. The Age of the Mother

If an expectant mother is more than 35 years of age then her chances of giving birth to a baby with trisomy increase. This is because as the woman ages the quality of her eggs deteriorates, increasing the possibility of there being chromosomal defects.

2. Deficiency of Vitamin B

In a lot of trisomy cases, it has been found the mother was deficient in Vitamin B, especially folic acid. This is one of the primary reasons women are put on folic acid supplements as soon as they conceive.

3. Presence of Teratogens

Teratogen is any substance that causes harm to an embryo. Teratogens interfere with the normal development of the embryo and can give rise to defects in your baby. Some commonly known teratogens are alcohol, smoking, tobacco, use of certain medicines, illegal drugs, bacterial or viral infections and radiation.

What Happens If Your Newborn Baby has Trisomy

If your baby has an extra chromosome, then in most cases it may lead to a miscarriage (even before your baby develops fully) or a stillbirth. If the baby survives with this defect, not only may she have a shortened lifespan, but she may also have various health complications. Here are some health conditions or diseases with the extra chromosome that a baby may have:

Trisomy 21 – Down Syndrome

As the name suggests, this abnormality arises in the chromosome number 21, and this is the most common abnormality of an extra chromosome. In approximately 90 per cent of the cases, the baby may get this abnormality from the mother’s side. Trisomy 21 or Down syndrome arises when a baby is born with a set of three 21 chromosomes.

Karyotype of person with Down Syndrome

Following are the types of Down syndrome:

  • Standard Trisomy 21: Every cell in the body has an extra copy of chromosome number 21. This happens as a result of faulty meiosis (i.e., either the egg of the sperm has an extra chromosome).
  • Mosaic Down Syndrome: Only some cells in the body have an extra chromosome number 21. This is usually a result of faulty mitosis (i.e. development of the foetus in the womb).
  • Translocation Down Syndrome: This usually happen when the extra copy of chromosome number 21 attaches itself to some other chromosome in the cell.

A baby born with Down syndrome may have hampered mental growth, heart defects, distorted facial features etc.

Trisomy 18 – Edward Syndrome

Babies with this chromosomal abnormality have three chromosomes of number 18. This abnormality is named after the doctor who first established this defect. Babies who are carried till full-term pregnancy have 50 per cent survival rate, and girls have better survival rate than boys.

Karyotype of person with Edwards Syndrome

This syndrome may occur in the following ways:

  • Full Trisomy 18: Every cell in the baby’s body has an extra chromosome.
  • Mosaic Trisomy 18: Extra chromosome in present only is few cells.
  • Translocation Trisomy 18: This is a genetic condition, and in this condition, the chromosomes may attach to each other.

The baby born with this abnormality may have cleft lip, defects in vital organs such as kidneys or heart, neural tube defects etc.

Trisomy 13 – Patau Syndrome

Trisomy 13 may result from the glitch in chromosome number 13.

Karyotype of person with Patau Syndrome

This condition may lead to:

Babies with trisomy 13 or 18 may die soon after birth; however, very few of them may survive up to the teenage years.

Signs of Trisomy in Pregnancy

Some signs of trisomy in pregnancy may include the following:

  • Lesser foetal movement.
  • Growth not at par with the gestational age.
  • The placenta is much smaller.
  • Only one umbilical cord artery may be present.
  • More amount of amniotic fluid around the foetus.

How Are Trisomy Disorders Diagnosed?

Your doctor may establish trisomy disorder through one of the following techniques:

  • Testing the amniotic fluid.
  • Through an ultrasound scan.
  • Screening the maternal serum.
  • Testing the sample of the cell from the chorion tissue or CVS.
  • NIPT or non-invasive prenatal testing of the foetal DNA.
  • Testing the baby’s blood after birth.
  • Testing of blood in the first and second trimester.
  • Along with a blood test, also studying the neck and back of the baby in an ultrasound scan.
  • Genetic counselling of women who are above 35 years of age.


Here are answers to some frequently asked questions about babies born with an extra chromosome:

1. Can an extra sex chromosome lead to any disorders?

Yes, sex chromosomes may lead to some complications, but these are less severe than the ones caused by non-sex chromosomal. Some of the disorders that may occur include XYY syndrome, Klinefelter syndrome (XXY), or Triple X syndrome.

2. Can the mother’s age increase the chances of Down syndrome in babies?

Yes. An older woman is more likely to give birth to a baby with Down syndrome. This is because her reproductive cells have an extra copy of chromosome 21, which may increase the risk. However, 75 per cent of babies born with Down syndrome are born to mothers who are 35 years or younger. Therefore, if you are more than 35 years of age, you may be recommended to undergo genetic counselling before you plan to conceive.

3. Are kids with the same chromosomal abnormality alike?

It is not necessary that children with the same chromosomal abnormalities be alike because the reaction of the body to the syndrome is dependent on the gene set-up and it is unique in every case.

4. Do siblings of a child with chromosomal abnormality also have the same problem?

It may not be the case because abnormalities in the chromosomes are usually accidental and thus it means that not all children born to a couple will have a same chromosomal abnormality. However, in case the abnormality is hereditary then the couple may have to undergo genetic counselling to rule out the abnormality in subsequent babies.

5. What are isodicentric chromosome 15 syndrome and chromosome 22?

Isodicentric chromosome 15 abnormalities may lead to developmental complications, which may lead to developmental delays, improper muscle tone, intellectual issues, weak facial features etc.

Whereas Isodicentric chromosome 22 is a rare condition that may occur due to extra chromosomes only in few cells of the body. This may lead to hampered mental growth, an improper growth of both the sides of the body, growth delays etc.

The chromosomal disorders are difficult to establish, especially when they occur along with the foetal growth. However, once your doctor is able to establish any chromosomal abnormality in your baby, you will be guided in the best possible manner.

As there is no curative therapy, genetic counseling has plays a central role in the management. The counselor will need to find out the family’s perceptions about the condition and important issues after the diagnosis like the cause, course, outcome, treatment options, blame, etc. These factors deserve special emphasis for the given family while giving them a realistic picture of the future.

Also Read: Edwards Syndrome in Infants 

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