Birth Defects
What is it?
A birth defect is an abnormality that is present at birth. There are over 3,000 different known birth defects. A birth defect can occur in any major organ and in any part of the body, and can range from minor to severe. Many birth defects lead to mental or physical disabilities, but some birth defects are fatal. They are, in fact, the leading cause of death in the first year of life. Birth defects are also called congenital
abnormalities.
Who gets it?
Around 3 to 4 percent of all newborns have a major birth defect. However, many birth defects are not evident until a child grows. For this reason, the rate of birth defects reaches about 10 percent by age
five.
What causes it?
Statistics show that around 60% of birth defects have an unknown cause. The others are caused by genetic or environmental factors, or a combination of the two. Genetically inherited birth defects occur when one or both parents pass along a defective gene to the child. In very simple terms, genes are carried on thread-like structures called chromosomes, and determine our individual characteristics, such as how we look. Just one missing or faulty gene can cause a birth defect. There are 46 chromosomes. One pair of chromosomes determines the child's sex. Boys inherit an X chromosome from the mother and a Y chromosome from the father. Girls inherit two X chromosomes. X-linked birth defects, such as hemophilia, are those that can only be passed on to boys by their mothers. These defects are only carried on the X chromosome. Because boys have only one copy of the X chromosome, which they receive from their mothers, a defective gene on the X chromosome causes problems. Because girls have two X chromosomes, an abnormal gene on one X chromosome might be balanced by a normal gene on the other X chromosome. Some birth defects are dominantly inherited, which means at least one parent must have the trait in order for the child to get it. Polydactyly (extra fingers or toes) is a dominantly inherited birth defect.
Some birth defects can occur only if both parents are carriers of the defect. This means they are healthy, but both have the defective gene, which they pass on to the child. This is called recessive inheritance. Recessive diseases are more severe than dominant diseases. Examples of birth defects caused by recessive inheritance include sickle cell anemia, Tay-Sachs disease, cystic fibrosis, and phenylketonuria (PKU). If only one parent passes along the recessive gene for a disorder, the normal gene received from the other parent will prevent the disease. However, that child will be a carrier for the disease. Children of a carrier have a 25% chance of getting the disease if the other parent is also a carrier. Birth defects, such as Downs syndrome, can also be caused by too many or too few chromosomes, or damaged chromosomes.
Environmental causes of birth defects include infections; poor prenatal care; use of drugs or alcohol by the mother during pregnancy, and exposure to chemicals, radiation, or diseases. Doctors use the term
"teratogen" to describe any substance that can cause abnormal development of the egg in the mother's womb. Infections that can cause birth defects include rubella, cytomegalovirus (CMV), syphilis, toxoplasmosis, Venezuelan equine encephalitis, and parvovirus. In rare cases, chicken pox during pregnancy can also cause birth defects.
Alcohol abuse during pregnancy can cause fetal alcohol syndrome, which includes mental retardation, low birth weight, and heart problems. Drugs that can cause birth defects include thalidomide, tetracycline, sulfa drugs, drugs used to treat tuberculosis and cancer, anticonvulsants, hormone supplements, recreational drugs such as LSD and cocaine, and certain drugs used to treat psychosis and anxiety. Some birth defects, such as neural tube defects and cleft lip and palate, are caused by a combination of genetic and environmental factors. These are called multifactorial birth defects. Birth defects are also caused by Rh disease, in which the mother's and baby's positive and negative blood factors (Rh factors) are not compatible. Too much or too little amniotic fluid can cause birth defects, or be a sign of a specific birth defect. Too little fluid interferes with the development of the lungs and
limbs.
What are the symptoms?
Symptoms depend upon the type of birth defect. Symptoms are classified as structural, if they involve a missing body part, or metabolic, if they involve a problem in body chemistry. Common structural defects include heart defects, spina bifida, cleft lip and/or palate, hyspospadias (in which the opening in a male baby's penis is in the wrong place), and gastrointestinal defects. Spina bifida is one of a group of birth defects called neural tube defects (NTDs). With spina bifida, the spinal column doesn't close completely around the spinal cord. Another NTD is anencephaly, in which parts of the brain do not develop. Metabolic defects include Tay-Sachs disease, which affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein.
Other common birth defects and their symptoms include: - Cerebral palsy, caused by brain damage. Children with cerebral palsy have difficulty controlling muscle movement. - Cystic fibrosis (CF), which affects the respiratory and digestive systems, with symptoms including chronic respiratory problems and pneumonia, bulky stools, and poor weight gain.- Down syndrome, characterized by mental retardation and distinctive facial and other physical features. Children with Down syndrome may also have heart defects and other health problems.- Fragile X syndrome, which affects boys more than girls and is characterized by various degrees of learning disabilities and mental retardation. These children also have distinctive features, such as a long face and flat feet.- Muscular dystrophy, which is a group of muscle diseases that lead to progressive muscle weakness and degeneration.- Sickle cell anemia, which affects mostly African-Americans and causes anemia and chronic pain.- Fetal alcohol syndrome, which causes delayed growth, mental retardation, disorders of the central nervous system, and abnormal facial
features.
How is it diagnosed?
There are many screening tests that can be performed during pregnancy to diagnose birth defects. These tests are routinely performed if the mother is over 35 years old or if there is a family history of birth defects. An ultrasound exam can be done during any stage of the pregnancy. This test uses sound waves to produce a picture of the fetus, and can detect spina bifida, limb defects, and heart and kidney problems. During the 16th to 18th week of pregnancy, a blood test that measures levels of alpha-fetoprotein (AFP) can identify neural tube defects in the fetus. During the 16th to 20th weeks of pregnancy, a small amount of amniotic fluid can be withdrawn from the mother's womb and tested for a number of genetic defects, including Down syndrome. Chromosome and some genetic disorders can be diagnosed as early as the ninth week of pregnancy through chorionic villus sampling (CVS). With this test, a fine needle is inserted through the abdomen or a flexible tube is inserted through the vagina. Both methods remove a small sample of the placenta. Keep in mind that most screening tests identify the possibility of a defect. These tests are not fail-safe, so it's important to discuss all options and further testing with your doctor to ensure your baby's health. Babies are also routinely screened after birth for birth defects that require immediate
treatment.
What is the treatment?
Treatment of birth defects depends upon the type of birth defect and how severe it is. Some require surgery to correct the defect at some point in the child's life. Others require a combination of medical and educational therapy as the child grows. Your doctor will help you understand your child's birth defect and the best course of
treatment.
Self-care tips
A healthy pregnancy goes a long way in preventing birth defects, and it all starts before you even become pregnant. If you are thinking about becoming pregnant, make sure you are aware of any family history of birth defects, on both your and your partner's side. Some birth defects cannot be prevented. However, if there is a history of birth defects, or you are considered high risk because of age, ethnic background, or health problems, you can receive genetic counseling and testing to help you in your planning. It's also important to make sure you have had all your immunizations; to avoid cigarette smoking, drugs, and alcohol; and to make sure neither you nor your partner has a sexually transmitted disease. Your diet is also important before and during pregnancy. It has been proven that taking a recommended daily dose of folic acid, found in foods such as leafy green vegetables, beans, and orange juice, actually reduces your risk of having a baby with neural tube defects. Neural tube defects are conditions involving the brain and spinal cord, such as spina bifida. Doctors recommend that all women of childbearing age receive 400 micrograms of folic acid per day. While many foods are now fortified with folic acid, many women still do not get enough folic acid in their diet. That's why your doctor will prescribe special prenatal vitamins to ensure you and your developing baby get the correct amount of important vitamins and minerals. If you must take any medications on a daily basis, check with your doctor to be sure they are okay to take during pregnancy. However, never stop taking any medication without checking with your doctor first. Regular exercise and plenty of rest also contribute to a healthy pregnancy.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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