Having a healthy baby is a joyful event for every couple and their families; however this happiness turns into feelings of guilt, stress and disappointment when the baby is born with some abnormality.

Birth defects are abnormality of structure, function or metabolism present at birth that results in physical or mental disabilities or death. Thousands of birth defects have been identified so far that lead to major health problems. About 5 percent of children worldwide are born with birth defects that are also often responsible for a considerable number of child deaths at the time of pregnancy, birth and during the first month of life.  30 percent of children born with birth defects are expected to die during infancy and another 30 percent are more likely to suffer from severe disability. A majority (about 75%) of these birth defects can be prevented, treated or rehabilitated for schooling, working and marriage, but often the treatment is lifelong and may be expensive.

The famous adage ‘Prevention is better than cure’ is so very true for birth defects. Luckily there are tests for both husband and wife, called Carrier tests, conducted before pregnancy to identify the carrier status for possibility of birth defects. Other tests, the prenatal tests are carried out during the three trimesters of pregnancy for detection of major abnormalities that might occur while baby is in the womb. These tests provide an opportunity to decide whether the couple wishes to conceive, continue or terminate the pregnancy on medical grounds.

Categories of birth defects

Birth defects are mainly caused by genetic and environmental factors, or a combination of both; however, the causes of about 70 percent of birth defects are still unknown. Following are the most common categories of birth defects:

A. Chromosomal Anomalies
Abnormalities in the number or structure of chromosomes can cause many birth defects. These are usually caused by an error that occurs during the development of the fetus. Because of the error, a baby can be born with too many or too few chromosomes or with one or more chromosomes that are broken or rearranged. Some common types of chromosomal anomalies are:

• Trisomy Disorder: This type of birth defect is caused by an alteration in the number or genetic structure of chromosomes. The most common type of Trisomy is Down’s syndrome, with an extra copy of chromosome. Affected children have varying degrees of intellectual disabilities, characteristic facial features and, often, heart defects and other health problems. The risk of having a child with Down syndrome increases with increased maternal age from 1 in 600 births for mothers under the age of 30 years to 1 in 50 births for mothers over 40 years.
  
• Sex Chromosome Abnormalities: Missing or extra copies of the sex chromosomes, X and/or Y affect sexual development and may cause infertility, growth abnormalities and behavioral and learning problems. However, most affected individuals live fairly normal lives. Examples include Turner syndrome (in which a girl is missing all or part of an X chromosome) and Klinefelter syndrome (in which a boy has one or more extra X chromosomes).

B. Single Gene Disorders
This type of abnormalities involves mutation or change in a single gene of human chromosomes. Common examples include:

• Thalassaemia – An abnormality in the production of hemoglobin
• Hemophilia – A blood-clotting disorder
• Sickle-cell anemia – Sickle shaped red blood cells gets infected with abnormal heamoglobin
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency – The body doesn't have enough of the enzyme G6PD which helps red blood cells function normally
• Achondroplasia – A form of dwarfism
• Tay Sachs disease – A fatal nervous system disorder
• Cystic Fibrosis – A serious disorder of lungs and other organs
• Duchenne muscular dystrophy – Progressive muscle weakness

C. Multifactorial Birth Defects
Some birth defects are caused by a combination of genes and environmental exposures; and are known to have multifactorial inheritance. In some cases, an individual may inherit one or more genes that make him or her more likely to have a birth defect if he/she is directly or indirectly exposed to certain environmental substances, such as cigarette smoke. These individuals have a genetic predisposition to a birth defect. But if the individual is not exposed to the environmental substance before birth, they probably will not develop birth defect, in the first place. Examples of multifactorial birth defects include:

• Cleft lip/palate – Opening in the lip and/or roof of the mouth)
• Neural tube defects (NTDs) – Serious birth defects of the brain and spinal cord, including spina bifida and anencephaly
• Heart defects – The most common type of birth defect and usually associated with majority of birth defect related deaths.

Factors associated with birth defects

• Advanced Maternal Age
• Advanced Paternal Age
• Maternal Malnutrition
• Consanguineous Marriages
• Maternal infections such as Rubella and Toxoplasmosis
• Poorly controlled maternal diabetes mellitus
• Unsupervised intake of medicines during pregnancy
• Folk remedies for abortions
• Inadequate dietary intake of foliate, vitamins, iron and iodine before and during pregnancy 
• Smoking, alcohol and drug addiction
• Exposure to X-rays and other mutagens

Strategies for prevention

Some genetic birth defects can be prevented from arising in the first place by targeting at their cause (primary prevention). Other defects can be avoided by early detection, appropriate management, identifying individuals and couples at risk, and by providing genetic counseling. The following interventions can be applied both before and during pregnancy:

I. Preconception Checkups

• Certain health conditions that are likely to pose a risk in pregnancy can be identified during preconception visits and treated. Such visit is especially crucial for women with chronic health conditions, like diabetes, high blood pressure and

  Myths about Birth Defects

  • Birth defects are rare
  • Birth defects are contagious
  • Birth defects are punishments from God for the sins of parents
  • Birth defects are mainly due to mothers
  • Birth defects are only caused due to marriages with blood relations
  • Birth defects cannot be prevented or cured
  epilepsy. For example, women with diabetes who have poor blood-sugar control are several times more likely to have a baby with a serious birth defect than women without diabetes. However, if their blood sugar levels are well controlled before pregnancy, women are likely to have a healthy baby.
• In the presence of a hereditary disorder, taking a good family history helps in detecting pregnancy risks. Carrier testing, genetic counseling and referral to specialized centers is offered to the couple.
• Reducing birth defects related to advanced parental age such as Down syndrome can be treated as part of the family planning services.
• Congenital rubella syndrome can be prevented by immunizing against rubella infection.
• Information regarding the deleterious effects on the developing embryo of smoking, alcohol intake, unsupervised medication, exposure to X-rays and certain mutagens / tetragons at the workplace should be made available to women prior to pregnancy.

II.    Use of Prenatal Diagnosis for Early Detection of Birth Defects
Some birth defects can be diagnosed during pregnancy by prenatal tests. The following 3 tests are commonly available at all leading tertiary care hospitals of Pakistan:

• Ultrasound can help diagnose structural birth defects, such as spina bifida, heart defects and some urinary tract defects.
• CVS is usually performed during the first trimester of pregnancy to diagnose or rule out chromosomal abnormalities, such as Down syndrome and many other genetic birth defects.
• Amniocentesis is usually done from 16 weeks onwards to detect Down syndrome and other chromosomal abnormalities, structural defects such as spina bifida and anencephaly and inherited metabolic disorders.

About the Writer:
Ms. Seema Lasi is affiliated with The Aga Khan University – Human Development Programme as a Senior Instructor. She has an academic background of Masters in Epidemiology & Biostatistics and Masters in Genetics. Her research interests are Early Childhood Growth, Promotion & Development and Childhood Injuries and Disabilities.