The Procedure of Fetal Karyotyping

The fetal karyotyping is performed in order to evaluate the chromosomal abnormalities associated with the fetus. 

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When a karyotype test is performed using fetal tissue (by amniocentesis) with an objective to rule out various chromosomal conditions before birth, the whole technique is known as a fetus or fetal karyotyping. 

The most trusted, versatile and traditional genetic technique, scientists using for a long time is karyotyping. It’s a process to study chromosomes (not DNA); their structure, number and other related conditions. 

More a manual method; karyotyping is now a key cytogenetic technique, researchers use in diagnosis as well. It can investigate and study various genetic disorders at prenatal and postnatal stag

The use of karyotyping in checking the genetic status of a fetus is employed widespread. Unknown random events during cell division and the effect of the environment cause an imbalance in chromosomes or alter the structure of chromosomes. 

Consequently, a baby may suffer from serious mental, developmental and reproductive abnormalities. Clear reasons in most of the cases are still unknown but taking some preventive measures during pregnancy may help. Here have written an article on it, you can read it here:

Chromosomal abnormalities such as down syndrome, Klinefelter syndrome and other structural problems are so common. If we can somehow diagnose the fetus early, we can make a decision to manage it. Henceforth it is a wise decision to check the chromosomal status of the baby prior to birth. 

Fetal karyotyping is widely used in the field of prenatal genetic testing for a long and it is the most-trusted method too. In the present article, I will explain to you fetal karyotyping, its importance and procedure. 

Though the sample collection process is different from conventional karyotyping, the entire process to get metaphases is almost the same. I will also explain to you the process and method of a fetus or fetal karyotyping, the technique of sample collection, advantages and limitations. 

What is fetal karyotyping? 

A developing embryo in a mother’s womb is a fetus. Genetic conditions that occur from birth are categorized into congenital genetic disorders and majorities are non-inherited and can’t be treated.

When a karyotype test is performed on the fetal sample using the cell culture technique, it is known as fetal karyotyping. The whole technique of testing a fetus is known as prenatal genetic testing. 

Moreover, FISH and microarray are two other testing method scientists uses beside fetal karyotyping to rule out genetic condition associated with the fetus.

In order to prevent the spreading of congenital conditions, it is very important to test it before birth, if detected we can manage it. Among many techniques, fetal karyotyping is a cost-effective and primary testing method to encounter many chromosomal defects.

Inherited genetic disorders:

When a genetic disorder passing from parents to their offsprings, it is known as inherited.

Role of genetic counseling: 

Usually, fetal karyotyping isn’t recommended for all. I mean, if a mother is healthy and doesn’t have any previous history, fetal testing isn’t required. The reason is the risk of miscarriage associated. The role of a genetic counselor is to let you know if fetal karyotyping is required or not!

So the genetic counselor first collects information from parents such as their previous history of any disorder, maternal age, or other disease condition. After gathering information, he or she advises either to go for fetal karyotyping or not. Here is the condition in which fetal karyotyping is required: 

  • Maternal age above 30 
  • Previous history of a genetic condition 
  • Any family history of a genetic disorder 
  • Any inherited genetic condition running in the family 
  • Any history of cancer or inherited cancer

In any of these conditions, medical genetic practitioners advise fetal karyotyping. 

Importance of fetal karyotyping: 

Usually, the fetal karyotyping or such type of related genetic testing are not recommended during the normal pregnancy. There are two reasons for that, first, not needed if everything is ok! And second, the genetic tests are actually costlier. 

But in conditions like the maternal age above 35, previous history of genetic disorders or indicated by a sonographer, a fetus karyotyping is performed. 

For example, the condition observed during the sonography in which a nasal bone is not observed, karyotyping is advised. It may result in Down syndrome.

Structural chromosomal problems like chromosomal deletion, duplication and translocations can be identified. Also, numerical chromosomal abnormalities are also characterized by the present method. 

The overview of the process of fetal karyotyping is explained here in the figure.

If you want to learn more about how a karyotype is performed, you can read this article: What is Karyotyping?- Definition, Steps, Process, and Advantages.

The brief overview of fetal karyotyping.

Process of fetal karyotyping: 

The whole process is divided into few steps listed below, 

  • Sample collection 
  • Cell culture 
  • Culture harvesting  
  • Microscopy 
  • Preparing a karyotype 

Sample collection: 

Two types of samples can be collected to perform fetal karyotyping- amniotic fluid (amniocentesis) and chorionic villi sampling. 

Amniocentesis: 

The important and crucial step in fetal karyotyping is sample collection. A process is known as “amniocentesis” in which a fluid or some tissues are isolated from a live fetus and is processed for karyotyping. 

Two types of samples are usually preferred; amniotic fluid and chorionic villi. The whole amniocentesis technique is an invasive method that includes painful procedures and the risk of miscarriage. 

Experts first perform an ultrasound to know the exact position of a baby in a womb. 

Afterward, inserts a thin, long, hollow needle from the abdominal wall to the uterus (It’s an invasive technique- the patient may feel pain). Carefully, the expert removes amniotic fluid using the needle. 

The amniotic fluid present in the amniotic sac is rich in fetus cells, approximately 10 to 15 ml collected, aseptically. 

Sample can be stored at -4°C temperature for further use. 

Soon after the sample is sent for karyotyping immediately, the karyotyping should be performed immediately within 24 hours of sample collection. 

After collection, the patient may feel pain, bleeding from the lower part or discomfort for a couple of days. Note that miscarriage may occur in some cases if not performed well. 

No post-processing is required for preparing an amniotic fluid for cell culture. 

Fetus karyotyping is performed by invasive methods like amniocentesis and chorionic villie sampling, although non-invasive methods like cffDNA- cell-free DNA testing aren’t used.

Chorionic villi sampling and processing: 

Another sample type for fetal or fetus karyotyping is the chorionic villi sample, abbreviated as CVS or CV sample. 

The chorionic villi is a solid tissue sample isolated from the wall of the placenta, rich in fetal cells. Placenta generally provides oxygen and nutrients to the fetus and thus has fetus cells. 

Tissues are removed from the abdominal wall or cervix known as transabdominal and transcervical sampling, respectively. Note that CVS is collected around 10 weeks of pregnancy. 

The collected sample is solid white tissue, stored in TE buffer or saline buffer for further use. It can also be stored in culture media (RPMI 1640). 

Before processing further, the chorionic villi sample must be prepared. Using TE buffer washing, maternal blood traces and other waste should be removed first. 

The sample is taken into an Eppendorf tube and TE buffer is added. Invert tubes several times and centrifuge them. 

Remove the TE buffer and add a fresh one to the pellets, repeat the process until clear pellets obtain. 

The sample is taken into a Petri dish, and TE buffer is added and again washed thoroughly. 

The prepared sample is send for fetal karyotyping.

Cell culture: 

The process of fetal karyotyping, as I said, is almost similar to the conventional karyotyping process. 

Using a ready-to-use culture media (especially for fetal samples), cells are cultured aseptically. 

Here the cells are culture under the aseptic conditions using the ready to fetal cell culture media. All the culture tubes or flask are placed for 72 hours at 37°C. At the end of incubation, colchicine is added to stop the process of cell division and immediately process cell harvesting. 


Read more on present topic: Cell Culture: Definition, Types, Media and Examples.


Karyotyping: 

The process of fetal karyotyping is much like the conventional PBLC with some modifications. 

Using the combination of methanol and glacial acetic acid, cells are harvested until clear pellets appear. After that, the slide is prepared and observed under the microscope to identify anomalies if any. 

The fetal karyotyping is an invasive and painful sample collection technique having chances of miscarriage. Hence it is not normally recommended by gynecologists. 

Although as we mentioned, in some special cases it is needed. 

Harvesting: 

Cells are harvested and cleaned using methanol, glacial acetic acid and repeated centrifugation. 

Microscopy:

Harvested cells are stained and/or banded using Giemsa stain and observed under a microscope. Varied chromosome banding patterns are observed. 


Read the whole process and protocol in our previous article, the link is given here: Explaining the whole karyotyping technique and procedure.


What is fetal karyotyping used for? 

Fetal karyotyping is advised, as we said in some cases where it is needed. To encounter serious chromosomal conditions related to health the fetal karyotyping is performed. 

Those commonly are structural chromosomal aberrations or numerical chromosomal aberrations. 

Conditions like trisomies, monosomies, deletions, duplications, translocation or inversions are common indications. Here are some common indications detected: 

Trisomy 21: 

Also known as the down syndrome is a mental condition that occurs by an event known as non-disjunction. Here an extra chromosome is added along with a pair. 

Cytologically it is written as 47, XX/ XY; +21. It is a kind of numerical chromosomal abnormality. 

Trisomy 18: 

Also known as Edward’s syndrome is a genetic condition associated with motor, mental and muscle problems. Cognitive problems are common as well. Alike down syndrome, it is occurred by non-disjunction, leads to triplication of chromosome 18. 

Cytologically it is written as 47, XX/XY; +18.

Philadelphia chromosome: 

Translocation, known as Robertsonian translocation between chromosome 22 and 9 cause a serious type of cancer. It causes chronic myeloid leukemia and occurs by birth. 

During the chromosome distribution in cell division, some portion of chromosome 9; q arm deleted and translocated to chromosome 22 at q arm. 

Klinefelter syndrome: 

The present condition is also a type of trisomy in the sex chromosome, commonly present in male individuals. Here with the X and Y chromosome, an additional X chromosome is also present. 

The condition is known as XXY or Klinefelter syndrome associated with male infertility and related conditions. 

Cytologically it is written as 47, XXY +X. 

Turner syndrome: 

Yet another sex chromosomal disorder is Turner syndrome or monosomy X in females. Here instead of the pair of X chromosomes, only a single copy of the X chromosome is present. 

The condition is known as XO or Turner syndrome associated with female infertility and present by birth. 

Cytologically it is written as 45, XO -X. 

Chromosome 5 deletion: 

Not so common, but a prevalent cytogenetic condition is the deletion of p arm of chromosome 5, often known as Cry-do-chat syndrome. In this condition, a baby’s cry looks like a cat. 

It includes a high pitch-cat-like cry having distinct facial features, mental retardation and developmental problems. Cytologically, it is written as 46, XX/XY; del5p. 

Besides the above listed common conditions, thousands of other indications related to cancer, mental retardation, developmental problem and infertility are also detected using the fetal karyotyping technique. 

Summary:

  • Turner Syndrome- Known as XO, is a condition in which a single X chromosome is absent in a female. 
  • Down syndrome– Known as trisomy 21 or T21 in which an extra chromosome 21 is observed with a pair. 
  • Edward’s syndrome– known as trisomy 18 or T18, is a condition of one extra chromosome number 18. 
  • Philadelphia chromosome– Inversion between chromosomes 22 and 9. 
  • Cri-du-chat syndrome– Deletion of P arm of chromosome 5. 

Note that alterations of more than 10 or 20Kb in size can only be detected using the karyotyping technique. To study mutations at a molecular level, DNA microarray, DNA sequencing, or PCR is performed. 

FAQs:

What can’t be detected using fetal karyotyping? 

Though fetal karyotyping is one of the most common prenatal genetic testing techniques, yet not used to detect every genetic disorder. Mutations at the DNA or gene-level can’t be encountered using the present technique. 

Technically, a portion of 10Kb to 100MB can only be detected, although other techniques are required to detect lower base-pair mutations. 

Noted, other cytogenetic techniques such as FISH- fluorescence in situ hybridization and chromosome microarray can screen more mutations precisely. 

Mutations fewer than 100kb can’t be detected precisely using fetal karyotyping. 

When to not go for fetal karyotyping? 

Commonly, fetal karyotyping isn’t required during normal pregnancy. It includes chances of miscarriage or fetal loss. It isn’t required, 

  • If the female is healthy 
  • Maternal age below 30 
  • Normal ultrasonic report 
  • No previous family history of a genetic condition 
  • Parently karyotype is normal

Which sample collection method isn’t useful for fetal karyotyping? 

A non-invasive technique known as cffDNA or cell-free fetal DNA can’t be used for fetal karyotyping. cffDNA relies on the use of free DNA fragments present in the maternal blood. 

To karyotype, we need cells with intact genetic material or all chromosomes present. Therefore non-invasive prenatal technique isn’t suitable for fetal karyotyping. 

Karyotyping of fetus done through which method? 

The fetus or fetal karyotyping is performed using an invasive technique known as amniocentesis (collection of amniotic fluid) and chorionic villi sampling. Both sample collection techniques include pain, collection through needle and chance of miscarriage and henceforth are invasive.  

We have explained it in our previous section please read it there. 

What fetal karyotping results show? 

The fetal karyotyping results only include a karyotype of a baby growing in the womb (not father and mother). It shows defects or chromosomal defects associated with the fetus if any.

Can amniocentesis and karyotyping results differ?

First, understand, that amniocentesis is a sample collection method in which amniotic fluid isolated from the fetus. The collected fluid or CV sample is then processed for karyotyping. Therefore, we can say amniocentesis is a step or part of karyotyping process. It’s a sample collection technique.

The final product of amniocentesis is the amniotic fluid, while the final product or we can say results of karyotyping is the karyotype of chromosome.

Which invasive method is used in fetal karyotyping?

Amniocentesis and chorionic villi sampling are two invasive technique used in fetal karyotyping. It includes painful process.

Conclusion:

For high-risk pregnancy, fetal karyotyping is must require. If your doctor indicates, please go for fetal karyotyping. Genetic conditions are incurable mostly and therefore, families have to suffer economically, socially, and emotionally.

High-end expertise and a specialized microscopy system are required to perform the fetal karyotyping because the sample used in it is so precious.

The amniotic fluid or chorionic villi sample can’t be repeated, it puts the fetus at risk and it must be processed in a single collection. Hence a person who is performing fetal karyotyping should be highly experienced. 

Also, the sample should be processed within 24 hours to get maximum output from it. 

If you want a completed protocol, chemical list and procedure of fetal karyotyping we can buy our upcoming ebook. 

We are planning an ebook on protocols of karyotyping from various samples and different methods of banding and staining to observe it. 

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