Congenital defects

In this article we will talk about congenital defects, genetic and otherwise, their causes and their implications.

Congenital Defects (CD)

Congenital defects are alterations that originate  at the moment of conception, before birth, or during pregnancy.

A birth defect or disease is a disorder, a significant abnormality in the appearance, structure, or function of a newborn’s body when it is born.

A defect is genetic, when it is due to one or more anomalies of the genotype, and derives from one or both parents. An inherited disease is always genetic, but not necessarily the other way around.

  • Congenital problems are relatively common: 2 to 3% of live births have one or more defects.
  • By one year of age, their number increases to about 5%, and this is because some defects that were not obvious at birth can only be detected later.

Birth defects can appear obvious on the outside, they can be hidden inside the body, or they can be due to chemical imbalances. For example:

  • a visible defect  could be the absence of an arm, or a  hemangioma  (which is a benign vascular tumor due to the proliferation of the blood vessel endothelium located on the surface of the skin);
  • an internal defect  could be a malformed kidney or a  ventricular septal defect  – the dividing wall between the right and left ventricles of the heart;
  • a chemical imbalance  could be  phenylketonuria (PKU) , which is a potentially serious inherited metabolic disorder that consists of a defect in a chemical reaction that results in severe mental retardation in the child.

As for the number of congenital defects, a child can be born,

  • either with only one of these problems : for example with the  cleft lip  (a fissure in the upper lip);
  • either with multiple defects:  for example with cleft lip together with  cleft palate  (a malformation of the palate), or again, with a cleft lip and cleft palate together with other defects associated with the brain, heart or kidneys.

The diagnosis of a defect can be made through prenatal diagnosis, during pregnancy, at the time of birth of the child, or later.

As we have said, not all birth defects can be detected from birth.

  • Some may not show up until the baby is several months old, such as sickle cell disease  (a defect in red blood cells that causes severe anemia and bone pain).
  • Others , such as a malformed kidney, could take years to discover.
  • Still others  may go undetected for many years: for example, Huntington’s disease or Huntington’s disease: an inherited condition in which those affected live normally for decades and – at some point – develop dementia in middle age and lose their control of their arms and legs. 

The causes of genetic defects

As we have just specified above, hereditary diseases are all genetic, but not all congenital diseases (that is, those present from birth) are also genetic.

In fact, birth defects can be caused by genetic factors, or by a series of environmental factors such as infections, radiation, or certain drugs taken during pregnancy.

However, the causes of most birth defects are unknown.

The most common genetic defects

About 20% of congenital defects are linked to genetic or hereditary factors: each cell of the human body, in fact, contains 46 chromosomes; each chromosome contains thousands of genes; each gene has “written within it a blueprint” which has the development or function of a particular part of the body.

The presence of too many, or too few chromosomes compared to what is necessary, therefore does not give the necessary or complete information for a correct development and for the right functionality of our organism. 

Let us now analyze one by one the most common genetic ones.

Down syndrome

An example of a genetic condition caused by too many chromosomes is  Down syndrome . Only in very rare cases does this syndrome have a  hereditary component .

  • Due to an accident during cell division, people with Down syndrome are affected by the presence of a third copy (or part of it) of a particular chromosome.
  • That too much, is responsible for the typical group of birth defects found in people who are affected.

Individuals with Down syndrome have mental retardation, muscle weakness, drooping eyes, low-set and malformed ears, an abnormal crease in the palm of the hand, and heart and intestinal defects.

Turner’s syndrome

In Turner syndrome, a disorder that affects only women, an X chromosome is missing, which is one of the two human sex-determinant chromosomes. This fact leads to some characteristics that are typical, such as short stature, learning disabilities, and atrophic ovaries.

Since each of the chromosomes controls the structure and function of a certain part of our body, people with defective genes will have corresponding defects. Turner syndrome  is not an inherited disease.


Hemophilia is an  inherited disorder  due to the absence of a blood-clotting chemical that is caused by a faulty gene.

sickle cell anemia and cystic fibrosis

Other examples of  genetic/inherited diseases  are, sickle cell disease  (which is a blood disease), and  cystic fibrosis  which is a disorder that causes progressive damage to the  lungs  and  pancreas .

spontaneous mutations

Some defective genes can also be due to accidental damage, a condition called spontaneous mutation.


Most cases of  achondroplasia  (a condition that causes extremely short stature and deformed bones) are caused by a “new” genetic damage: that is, the mutation of a particular gene not present in the parents.

Their other possible causes

About 10% of birth defects are caused by environmental factors, such as infections, radiation, and medications taken during pregnancy.

The incidence of these environmental factors may vary depending on when this exposure occurred during pregnancy.

They can have serious consequences such as death; they can cause serious birth defects, but they can also have no effect. 

After its conception, the child is in fact in the following two stages of development (which are the main ones in this respect).

  1. The first stage is the embryonic stage , and includes the first 10 weeks of pregnancy. During this stage, most of the organs and systems of his body are formed.
  2. The second stage is the fetal stage , and includes the rest of the pregnancy. This stage is the period of growth of organs and the fetus in general.

The baby is most vulnerable during the embryonic stage, when its organs are developing. In fact, infections, radiation and drugs cause the greatest damage when exposure occurs between the second and tenth weeks after conception.


Rubella   is an example of an infection that causes birth defects if a woman gets it while pregnant .

The type of birth defect that results at birth depends on the developmental stage at which the infection occurs.

Rubella can lead to cataracts and deafness if the infection occurs during the 9th week, and cause heart defects if the infection occurs between the 5th and 10th weeks of pregnancy.

the radiation

Radiation during the first 3 months of pregnancy is another factor capable of causing some birth defects such as  microcephaly  (small head), spina bifida (a hole in the back that marks the premature end of spinal nerves), blindness or cleft palate which is a malformation of the palate.

medicines and recreational drugs

Many medicines and recreational drugs can also cause birth defects: these are all the more serious if the drugs are used during the first 3 months of pregnancy.

Thalidomide, an anti-nausea drug that was prescribed in the 1960s, caused a serious birth defect called phocomelia (it involved missing most of the arm, with the hands extending from the shoulders).

the alcohol

Alcohol is perhaps the most common substance capable of causing birth defects.

Fetal alcohol syndrome is the term that is used to describe those typical defects (learning disabilities, mental retardation, irritability, hyperactivity, poor coordination and abnormal facial features) due to the use of alcohol by the mother.

Indeed, this early vulnerability of the developing child has serious consequences.

A woman may not have known that she is pregnant for several weeks and may unknowingly expose her unborn child to the effects of medicines, X-rays, recreational drugs or alcohol during this most vulnerable time.

the uterus

Another type of environmental factor that can cause birth defects is related to the fact that the child has to grow up in the uterus.

The human fetus grows in its mother’s uterus and is surrounded by amniotic fluid (as if suspended in a bag of water) which cushions mechanical damage.

When the fibrous sac that holds this fluid ruptures, the bands of fibers from the torn sac can press on the fetus and cause amniotic band syndrome (which leads to the amputation of an arm or leg).

An inadequate amount of amniotic fluid can therefore put too much pressure on the entire baby, resulting in pulmonary hypoplasia (lack of lung development).

unexplained causes

Medicine has identified the causes of about 30% of birth defects, which means that about 70% of these still remain without an explanation.

These congenital malformations are difficult to classify, and may have multifactorial causes. This means that the defect is not caused by a single factor, but by a complicated combination of both genetic and environmental factors.

folic acid (vitamin M, or vitamin B9)

An insufficient intake of folic acid by those pregnant women who have a slight deficiency, in some cases can be the cause of spina bifida.

If a folic acid supplement is taken before and during pregnancy, this defect does not appear. So the problem occurs in the children of those women who have a faulty chemical reaction and who do not take folic acid supplements .

To remember:

Many birth defects can be avoided: if you are expecting a child or planning a pregnancy, do not take any medications or supplements without first consulting a doctor.

Birth defects: the implications

The subject of birth defects is quite complicated and has a strong emotional impact. This is because these are common problems that can be caused by many different genetic and environmental factors.

The fact that most of these problems occur without a known cause is frustrating for both parents and doctors as well.

The subject is particularly sensitive for parents who are understandably and deeply shocked when they learn that their child has a serious birth defect.

  • Many parents believe that medical science should be able to prevent, or at least identify in advance all possible birth defects.
  • They often tend to blame someone or themselves. Mothers, in particular, may blame themselves for fear that they did something that caused the defect, or for not doing something that could have prevented it. In reality, this is almost never the case.
  • Sometimes parents are convinced that the obstetrician (the specialized doctor who follows women during pregnancy, childbirth and hospitalization) is responsible. They think the obstetrician could have ordered a test, prescribed a medicine, or done something different to prevent the defect from appearing. This is not usually the case, but an honest and open discussion with your child’s doctor will help you understand if someone is at fault.

Parents of a child with a birth defect should schedule several discussions with the doctor, especially at times when both may be present. Parents and doctor should discuss thoroughly possible causes, tests, treatments. Parents should continue these discussions with specialists and support groups until they are completely satisfied.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

Leave a Reply

Your email address will not be published. Required fields are marked *