Abnormalities In Pregnancy - How Genetic And Chromosomal Defects Can Cause Miscarriage?
Being pregnant can give blissful joy of having a baby as well as insecurities that come along with it. Some fortunate to-be-mothers would easily progress through ups and downs of pregnancy, while some other might not be successful. These are some unlucky women that would face some unusual abnormalities in pregnancy that would eventually lead to miscarriage or abortion. We will discuss one such factor in this topic.
Chromosomal and Genetic abnormalities in Pregnancy
Chromosomes are important part of human body cell that contains genes. These genes contains specific information and instructions that determines physical characteristic, blood type, risk of getting specific diseases as well as thousands of biochemical processes.
A chromosomal abnormality in pregnancy occurs when fetus carries either incorrect number of chromosomes or chromosomes that are structurally faulty. These abnormalities or flaws in chromosomes can lead to birth defects, disorders such as Down syndrome and in severe cases, miscarriage.
What statistics tells us about chromosomal abnormalities?
According to WHO, out of 26 million birth in India every year, 2-3 percent accounts for some sort of chromosomal abnormality. That’s simply translates to birth of 5-6 lakhs babies with genetic disorders. According to some experts, severe cases of birth defects range between 25,000 and 40,000 annually.
Human body is made up of cells and each cell contains 23 pairs of chromosome, 46 in total. Out of these 46 chromosomes, half comes from sperm of the father and half of these are derived from the egg of the mother. Out of these 23 pairs of chromosomes, 22 pairs are known as autosomes while the remaining two called as allosomes.
These allosomes are also known as sex chromosomes that determines sex and sexual characteristics of a person. Where female has two X chromosomes (XX), male has two X and Y chromosomes (XY). A healthy baby should be getting equal amount of these chromosomes, else there are chances of genetic abnormalities.
Relation between Chromosomal abnormalities and Miscarriage
Chromosomal and genetic abnormalities are one of the major causes of miscarriage, especially during the first trimester. The errors or faults in chromosomes can prevent a fetus from developing properly. When this situation occurs, the immune system of the mother will react spontaneously and terminate the pregnancy.
- Various researches suggest that in about 60-70 percent of first time miscarriages, chromosomal abnormalities plays spoilsport. Though in most of the cases, the error is irregular means it does not affect subsequent pregnancies.
- In many cases, a disorder called trisomy is responsible for miscarriages. In trisomy, there are three instances of chromosome instead of two. Trisomy can occur in any of the chromosome but trisomy 16 and trisomy 9 are the most common types that are responsible for about 13 percent of all miscarriages in the first trimester.
In other cases, a chromosomal disability may result in a rare condition called molar pregnancy. There are two types of molar pregnancy; complete and partial.
- In complete molar pregnancy, the egg that comes from the mother has no genetic information that ends up look like a cluster of grapes. Fetal development does not occur in this case.
- In partial molar pregnancy, an egg is fertilized by two sperm instead of one. It also means the embryo gets two chromosomes from father and one from mother. This results in abnormalities in the baby.
Relation of Down syndrome with chromosomal abnormalities and miscarriages
Down syndrome also known as trisomy 21, is a common genetic disorder caused by an extra copy of chromosome 21. In Down syndrome, the baby is born with physical characteristic such as small stature, low muscle tone, small chin, flat nasal bridge and slanted eyes. Down syndrome is one of the most common genetic disorders prevalent in India.
- Down syndrome can also cause miscarriage and stillbirth. According to an estimate, about 30 percent of all Down syndrome pregnancies that are not terminated, end up in miscarriage or stillbirth.
- Advanced maternal age is considered as the biggest risk factor of having a child with Down syndrome. As woman grows older, the chances of Down syndrome increase accordingly. About 80-85 percent of children born with Down Syndrome are born to mothers aged under 35.
Besides Down syndrome, there are other disorders caused by presence of extra chromosome. These are:
- Trisomy 18 or Edwards Syndrome - Characterized by low birth weight and abnormally shaped head.
- Trisomy 13 or Patau Syndrome - Characterized by extra fingers, underdeveloped eyes, heart defects and intellectual disabilities.
- Klinefelter syndrome or XXY syndrome - This condition is the result of extra X chromosome in males which is characterized by sexual dysfunctions, little body hair, weaker muscles and reduced strength.
Diagnosis - Testing for chromosomal abnormalities
Analyzing cells of the fetus is the only way to detect chromosomal abnormality. You would go through ultrasound, various blood tests and other minimally invasive tests such as:
- Aminocentesis - Usually performed after the start of the 15 week pregnancy, this test analyzes sample of the amniotic fluid that surrounds the fetus.
- Chorionic villus sampling (CVS) - The test investigates the sample of the placenta. It is conducted on woman with 11 weeks of pregnancy.
Are there any treatment options?
There is no treatment known to medical science for chromosomal abnormalities. If the doctor is able to make correct diagnosis, you might be advised to terminate the pregnancy. This decision solely rest with the prospective parents. Some parents may choose to continue.
For women who are planning to conceive or already expecting or had history of some sort of chromosomal abnormalities during pregnancy, they must consult a gynecologist. She might refer you to a genetic counselor. By assessing medical records and family history, the genetic counselor can help determine the probability that your baby will be born with chromosomal defects.