Pregnancy can be a worrisome time for some parents-to-be. You may find yourself wondering daily about your baby’s prenatal health, happiness, and development. Genetic disorders are often of special concern to many expectant couples.
Genetic disorders can put your baby at risk for slow mental and physical development, physical defects, and lifelong illnesses. However, new screening tests are now available to help detect these genetic disorders before your baby is born. These can help to ensure that your baby receives the appropriate medical attention and treatment after birth.
What are Genetic Disorders?
Genetic disorders are physical defects or illnesses that are caused by problems in your body’s genetic code. Everybody is made up of 46 chromosomes, and these chromosomes carry your DNA. DNA is responsible for dictating how you will look, act, and develop. When a baby is conceived, he receives 23 chromosomes from his mother and 23 chromosomes from his father.
These chromosomes come together to complete an entire genetic code. Sometimes, however, defects can occur in some of the chromosomes or individual genes. As a result fetal development can change, and your baby can be born with a genetic disorder.
How are Genetic Disorders Transmitted?
Some genetic disorders are hereditary. Parents can sometimes carry a defective gene inside of their DNA. When two parents with the same defective gene conceive a child together, their baby will also be born with this defective gene.
This can sometimes result in a genetic disorder. While chromosomal disorders can be hereditary, they can also develop after fertilization, as the embryo splits during development.
Common Genetic Disorders
There are many different types of genetic and chromosomal disorders. It is important to be aware of these disorders so that you can assess your baby’s risk of developing one.
Sampling Methods to Detect Fetal Anomalies
Over the recent decade scientists have developed what is referred to as non invasive prenatal testing. This test can be used to determine whether the unborn baby is suffering from a number of chromosomal anomalies including Down’s syndrome.
The non invasive test aimed at detecting Down’s is referred to as an NIPT Down’s syndrome test. The only NIPT tests currently available are trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome).
The most significant advancement of non invasive prenatal testing is that, unlike invasive sampling methods such as amniocentesis, a non invasive test carries zero risk. Sampling is done using maternal blood samples from which cell free fetal DNA is extracted and analysed. Non invasive testing currently used to detect Down syndrome has a very high detection rate.
However, NIPT testing is still not as accurate as invasive sampling methods such as amniocentesis. It is useful in excluding the possibility of Down syndrome but if the result shows a high probability that they baby is a Down’s, invasive testing such as amniocentesis or CVS will still be recommended.
Sampling of fetal DNA from maternal blood is also used for non invasive prenatal paternity testing, a risk free way of establishing paternity in pregnancy that is offered by several DNA testing companies including Who’zTheDaddy?, easyDNA, homeDNAdirect and others.
Invasive Sampling Methods
Different fetal DNA sampling methods are carried out depending on the week of pregnancy. The earliest test to be carried out is called chorionic villus sampling and can be carried out at around 11 weeks. The procedure involves the extraction of a sample of chorionic villus from the womb lining. Extraction is done either by the insertion of a catheter through the opening of the womb (cervix) or by inserting a needle through the abdomen.
The entire procedure is done by a qualified OBGYN and insertion of the needle or the catheter in the right place is ensured by using an ultrasound. The chance of a miscarriage following this procedure is of around 1 in every 500.
A fetal sampling method that can be carried out just a bit later is known as amniocentesis. This procedures is done in much the same way as chorionic villus sampling – a needle is inserted into the womb guided by an ultrasound. What is different for this test is that the sample is extracted is a sample of amniotic fluid. Woman who conceive over the age of 35 are often advised to undergo amniocentesis as their risk of having a child with an abnormality increases.
This procedure can help determine whether the unborn baby suffers from any neural spine defects but assessing the levels of alpha-fetoprotein. Alphafeto protein is only found in amniotic fluid and thus, analysis would not be possible with chorionic villus sampling. The incidence of miscarriage with amniocentesis is around 1 in every 500.
The fetal sampling method that can be carried out in the most advanced stage of pregnancy is known as Percutaneous umbilical cord sampling- this procedure is rarely used as the risk of miscarriage is very high. However, if the fetus needs a blood transfusion due to for example anemia, the blood needed can be transferred using this procedure.
Downs Syndrome
Downs Syndrome is actually a chromosomal disorder, caused by the presence of an extra chromosome. In this case, instead of having two of chromosome 21, your baby will have 3. This is why Downs Syndrome is sometimes referred to as Trisomy 21.
Downs Syndrome is characterized by delayed physical and mental development. Children with Downs Syndrome tend to have slower language skills and a lower IQ. Other physical characteristics of Downs Syndrome include a smaller head, a broad, flat face, and small ears.
Downs Syndrome affects 1 out of every 1,000 children born in the United States, however, your risk for having a baby with Downs Syndrome increases with maternal age. Women who are 35 have a 1 in 350 chance of having a child with the syndrome, while women who are 45 have a 1 in 30 chance.
Sickle Cell Anemia
Sickle cell anemia is a hereditary disorder that is passed down from both parents. It causes red blood cells to take on an abnormal sickle-shaped appearance, which results in chronic anemia. Sickle cell anemia can also cause episodes of severe pain and a number of other health related illnesses. About 70,000 children in the United States are currently affected by sickle cell anemia. The disease is most common among people of African or Latin American descent, though it can affect a child of any background or culture.
Tay-Sachs Disease
Tay-Sachs disease is a devastating illness that causes severe mental and physical incapacity. A hereditary disease, this illness can be passed on to your baby if both your and your partner are carriers of the Tay-Sachs genetic defect.
Symptoms of the illness generally appear a few months after birth and gradually worsen. They include blindness, seizures, dementia, and paralysis. Most children born with Tay-Sachs disease die before the age of five. This illness is most common among people of Ashkenazi Jewish or French Canadian descent.
Phenylketonuria (PKU)
PKU is a genetic disorder that affects children who have parents who carry the PKU genetic defect. This disorder affects how the body processes protein, and, if left untreated, can lead to severe developmental and physical delays. It can trigger mild to moderate mental retardation. About 1 in 10,000 children are born with this disease every year in the United States.
Fragile X Syndrome
Fragile X Syndrome is caused by a defect in one of your baby’s X chromosomes. It is typically passed on through the mother and affects male children, although female children can also be affected. Fragile X syndrome is characterized by late physical and mental development as well as particular physical defects.
Children with Fragile X syndrome tend to have a prominent chin, highly flexible joints, and long fingers. They also experience varying levels of impaired mental growth. Every year, about 1 in 2000 males and 1 in 4000 females are affected by Fragile X syndrome.
Testing for Genetic Diseases
Thanks to new technological advances, it is now possible to screen for many genetic birth defects and disorders before you conceive a child. If you have any risk factors for genetic diseases, it is possible for you to speak with a genetic counselor and get tested to find out if you carry any genetic defects that may be passed on to your future children.
Common risk factors include:
- having a family history of genetic disease
- having a child with a genetic disorder
- being of advanced maternal age
Screening tests are often simple and straightforward, requiring only a blood or saliva sample. It is also possible for you to screen your child for some genetic disease while she is still in utero. Pregnancy test procedures often involve the use of ultrasound, amniocentesis, or chorionic villi sampling (CVS) to detect physical abnormalities or genetic defects.
It is now possible to do prenatal screening for:
- Down Syndrome
- Tay-Sachs Disease
- Sickle Cell Anemia
