IRCID

Risk Factors

Chromosomal Abnormalities / Congenital Heart Defects / Neural Tube Defects / Cleft Lip & Palate

Chromosomal Abnormalities

What are they?
Chromosomal abnormalities - extra or missing genetic material visible under the microscope - cause unusual physical features, structural birth defects and mental retardation.

Chromosomes are packages of genetic information found in the nucleus of a human cell. Each cell contains pairs of chromosomes, one inherited from the mother and one from the father. There are 23 pairs of chromosomes - 22 autosomes and an X or Y sex chromosome. Together, these chromosomes contain about 100,000 genes.

The most common chromosomal abnormality is Down syndrome. This syndrome results from an extra chromosome #21. It is also referred to as trisomy 21.

How are they detected?
Chromosome abnormalities are detected by analyzing white blood cells or from a prenatal specimen. The chromosomes can be seen as banded strings under the microscope.

Prenatal diagnosis for chromosomal abnormalities is offered to all women in Iowa and includes:

Amniocentesis - The recommended study for prenatal diagnosis of a chromosomal abnormality. The test involves sampling the amniotic fluid (fluid surrounding the baby) for fetal chromosome analysis.
Prenatal ultrasound - In an ultrasound test, high frequency sound waves are bounced off the fetus creating an image of both the outside and some internal organs of the fetus. These images detect some chromosomal abnormalities.
Maternal triple screen - Formerly called the alphafetoprotein or AFP test, three tests are now done on a single sample of the mother's blood. Abnormalities detects in these tests suggest the possibility of chromosomal abnormalities. Additional tests such as an amniocentesis or an ultrasound are needed to confirm these screening test results.

What are they?
In Iowa, 13 of every 1000 births result in an infant with a congenital heart defect. Many of these defects are relatively minor; however, malformations of the heart are the leading cause of premature death from birth defects. Three of the most common heart defects are Tetralogy of Fallot, Transposition of the Great Vessels and Ventricular Septal Defect.

Tetralogy of Fallot is the most common congenital heart defect that results in a "blue baby." This defect involves an obstruction to the usual blood flow through the heart and this results in blood that does not carry enough oxygen. Infants with Transposition of the Great Vessels have a reversal of the aorta and the pulmonary artery. This results in two separate circulation systems for the blood in the heart. The most common congenital heart defect is Ventricular Septal Defect. This defect is an abnormal opening between the two ventricles (pumping chambers) of the heart.

How are they detected?
A baby who is "blue" after birth or who has an abnormal heart murmur will be evaluated by a pediatric cardiologist. Some congenital heart defects can be detected using a stethoscope; others can be detected using an electrocardiogram. Conformation of a heart defect may require an ultrasound examination.

In most instances, the cause of the congenital heart defects is unknown, but in about 10% of children, a cause can be identified. These causes fall into one of four categories: chromosomal abnormalities, single gene defects, environmental factors and familial factors. Infants born to diabetic mothers, mothers who have rubella during pregnancy, mothers who drink alcohol while pregnant, mothers on anticonvulsant therapy or mothers exposed to some other drugs or chemicals at work or in the home, are all at increased risk of congenital heart defect in their infant. The greatest risk factor is a family history of a congenital heart defect in a parent or older sibling.

What are they?
Neural tube defects are a group of disorders caused by failure of development of the structures which form and enclose the spinal cord and brain. These conditions are among the most common birth defects, affecting about 1 in 1,000 infants born in Iowa or about 40 cases per year. Approximately half of these defects are openings in the spine (spina bifida), which lead to a loss of sensation and muscle control below the opening. In the remainder of cases, the top of the brain and skull do not develop. This condition, called anencephaly, leads to death of the infant.

How are they detected?
A protein called alphafetoprotein (AFP) is made in the fetal liver. When a fetus has an open neural tube defect, this protein leaks through the defect and becomes elevated in the bloodstream of the mother. Roughly 85% of neural tube defects can be detected by measuring AFP in the mother's blood between 15 to 20 weeks of pregnancy. If the AFP is elevated and the fetus has a neural tube defect, an ultrasound (using sound waves) can usually determine the location and extent of the neural tube defect.

What are the risk factors?
An insufficient level of folic acid is a risk factor for neural tube defects. Women who take a multivitamin containing folic acid every day can decrease their chance of having a child with a neural tube defect by up to 50%. The risk also decreases in women eating a diet with higher levels of folic acid. The neural tube closes within 28 days after conception, often before a woman is aware she is pregnant. For this reason it is important that folic acid be taken before beginning a pregnancy.

What are they?
Clefts of the lip and/or palate are caused by disturbances in the embryo or fetus usually between 6 and 12 weeks after conception.

In some children, clefts of the lip and palate occur together. Clefts of the lip typically occur in the space stretching from one or both nostrils to the upper part of the lip. Clefts of the palate, or the roof of the mouth, can occur in either the front part of the palate, which has underlying bone, or in the back portion of the mouth, the so-called 'soft palate.'

How are they detected?
Clefts of the lip are immediately apparent at the time of birth. Clefts of the palate may not be immediately visible, but are readily detected when an infant is examined with its mouth open or crying. Some clefts may also be detected on a prenatal ultrasound exam.

What are the risk factors?
Risk factors for clefts of the lip and/or palate are varied and include environmental factors with evidence already being documented that alcohol and smoking can contribute to such clefts. In addition, genetic factors can be identified in some specific families. If there is a family history of a cleft or the lip and/or palate, there may be an increased risk of a cleft in the fetus.

Folic Acid: Prevention Strategy
Investigations over the past twenty to thirty years have demonstrated that folic acid, a B vitamin, is critical for the normal development of a human fetus. The primary benefit of adequate intake of folic acid is a reduction of a category of birth defects known as neural tube defects. These defects represent a failure of normal closure of the spinal canal (spina bifida) or failure of the top portion of the skull and brain to develop (anencephaly). Folic acid is essential for rapid cell division essential to make tissues and organs in the fetus. More research is needed to understand specifically how folic acid works.

If a woman has delivered a child with a neural tube defect, the risk this will happen in a subsequent pregnancy is about 3%. In this circumstance, a prescription for folic acid will be given to the mother. She will be instructed to take of folic acid daily from 1 to 2 months prior to any subsequent attempt to conceive another child and through the months of the pregnancy.

A major public health effort is underway to educate the population about the benefits of adequate consumption of folic acid. The U.S. Public Health Service has recommended that all women of reproductive age consume 0.4 milligrams of folic acid daily. To help insure that more women are adequately supplemented, the Food and Drug Administration has fortified grain products with increased folic acid. A healthy diet which emphasizes fresh fruits, green leafy vegetables (e.g.,spinach, broccoli, asparagus), orange juice, enriched whole grain foods and fortified cereals will allow some women to achieve the recommended daily intake of folic acid.

However, many women will remain undersupplemented. While fortification offers some protection, this strategy is not optimal unless used in combination with a vitamin supplement. The current recommendation therefore, is…

Other health benefits may also be associated with the daily consumption of adequate folic acid. Abnormalities in the development of the heart, limbs, urinary tract, lips and palate may be decreased. However, more studies need to be done to know definitively whether folic acid will decrease these defects, as has been the case for neural tube defects.

There are also studies which show that some of the more serious health problems which affect adults, such as heart attacks and strokes, may occur less frequently in individuals who consume the recommended daily dose, 0.4 milligrams of folic acid. More research is needed to clarify the effects of folic acid in the prevention of these types of diseases, but the message is clear regarding the potential benefits related to consuming folic acid starting in the teen years and continuing throughout life.