Birth Defect Research Paper
Defects
Like most expectant parents, you probably alternate between fantasies about a healthy baby and worries that your baby will have a health problem. Or perhaps you've been told throughprenatal screening that your baby might be born with a birth defect.
Many parents assume that all birth defects are severe or even fatal, but the fact is that many are treatable, often immediately after birth — and sometimes even before the baby is born.
It's especially important to know the risk factors involved and how to prevent birth defects. However, it's also important to realize that most babies born with congenital defects are born to two healthy parents.
About Birth Defects
Birth defects are defined as abnormalities of structure, …show more content…
function, or body metabolism that are present at birth. Major birth defects are abnormalities that lead to developmental or physical disabilities or require medical or surgical treatment. There are more than 4,000 different known birth defects, ranging from minor to serious, and although many can be treated or cured, they're the leading cause of death in the first year of life.
According to the March of Dimes, about 150,000 babies are born with birth defects each year in the United States. The American College of Obstetricians and Gynecologists (ACOG) says that 3 out of every 100 babies born in the United States have some kind of major birth defect.
Birth defects can be caused by genetic, environmental, or unknown factors. For most birth defects, the cause is believed to be an interaction of a number of genetic and environmental factors.
Structural or metabolic defects are those in which a specific body part is missing or formed incorrectly; metabolic birth defects are those in which there is an inborn problem in body chemistry. The most common type of major structural defects are heart defects, which affect 1 in 150 babies in the United States.
Other common structural defects include spina bifida, cleft palate, clubfoot, and congenital dislocated hip.
Metabolic defects affect 1 in 3,500 babies and usually involve a missing or incorrectly formed enzyme (a protein necessary for processing chemical substances in the body). Most children with a metabolic birth defect do not have any visible abnormalities, but metabolic defects are usually harmful or can be even fatal. Metabolic defects include Tay-Sachs disease, a fatal disease that affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein.
Defects caused by congenital infections result when a mother gets an infection before or during the pregnancy.
Infections that can cause birth defects include rubella (German measles),cytomegalovirus (CMV), syphilis, toxoplasmosis, Venezuelan equine encephalitis, parvovirus, and, rarely, chickenpox. None of these affect 100% of babies whose mothers are infected during pregnancy. If the mother is infected during early pregnancy, rubella carries the highest risk for birth defects (approximately 20%). Because of nearly universal immunization in the United States, rubella is very, very rare and the congenital rubella syndrome is almost never seen. CMV is probably the most common congenital infection and may be associated with intellectual disability (mental retardation) and hearing …show more content…
loss.
Other causes of birth defects include alcohol abuse by the mother. Although a few medications, such as medicines used for epilepsy, are associated with increased risks for certain birth defects, most commonly prescribed drugs are not associated with a significant risk of birth defects.
Birth Defects: Causes and Statistics
By: Ingrid Lobo, Ph.D. (Write Science Right) & Kira Zhaurova, M.S. (Nature Education) © 2008 Nature Education
Citation: Lobo, I. & Zhaurova, K. (2008) Birth defects: causes and statistics. Nature Education 1(1)
Every year, about 7.9 million infants (6% of worldwide births) are born with serious birth defects. With the causes of over 50% of birth defects unknown, how do we diagnose and prevent them?
Every year, an estimated 7.9 million infants (6% of worldwide births) are born with serious birth defects. Although some congenital defects can be controlled and treated, an estimated 3.2 million of these children are disabled for life. Moreover, birth defects are the leading cause of infant mortality in the United States. But where do these defects come from? Although some birth defects are inherited, others are a product of harmful environmental factors known as teratogens, and still others are multifactorial, resulting from a complex interaction of genetic and environmental influences. However, in approximately half of all birth defect cases, the causes are unknown (Christianson et al., 2006).
Genetic causes of birth defects fall into three general categories: chromosomal abnormalities, single-gene defects, and multifactorial influences. Prenatalenvironment can play a major role in the development of defects in all three categories, especially those linked to multifactorial causes.
Chromosomal Abnormalities
A person's genetic makeup is determined at conception. It is then, during the nuclear events of fertilization, that the genetic causes of many birth defects are determined. For example, chromosomal abnormalities, or large-scale duplications or deletions of chromosomal segments or entire chromosomes, can become apparent during this period. Many zygotes that carry such abnormalities do not develop into embryos, but among those that are carried to term,trisomy 21 (Down syndrome), trisomy 13 (Patau syndrome), and trisomy 18 (Edwards syndrome) are the most frequent birth defects. Embryos with these three conditions will develop severe disabilities regardless of the environmental factors associated with the pregnancy.
Unlike Down syndrome patients, who usually have a relatively long life span, children with Patau and Edwards syndromes often die soon after birth (March of Dimes, 2006). Individuals diagnosed with Patau syndrome suffer from neurological problems, mental and motor deficiencies, and polydactyly (Figure 1), as well as eye, heart, and spine defects (Patau et al., 1960). Those born with Edwards syndrome suffer mental retardation, breathing and feeding difficulties, delayed growth, and malformations of the kidneys, intestines, and heart (Edwards et al., 1960; Van Dyke & Allen, 1990). Thankfully, both of these devastating syndromes are rare.
Figure 2: Primary Down syndrome is caused by the presence of three copies of chromosome 21.
(a) A child who has Down syndrome. (b) Idiogram of a person who has primary Down syndrome.
Copyright National Institutes of Health.
Down syndrome, on the other hand, is by far the most common chromosomal abnormality, affecting 1 in 800 babies. The risk of having a child with this condition increases with maternal age, rising exponentially after a woman reaches age 35. For instance, in young mothers, the frequency of trisomy 21is about 1 in 2,000, but this frequency rises to 1 in 100 when a woman is 40 and to 1 in 12 when she is 50 years old (Figure 2). People who have Down syndrome suffer from moderate to severe mental retardation and a wide variety of health problems, including heart defects, leukemia, and Alzheimer'sdisease. The severity of these defects varies widely, however, and the majority of people with Down syndrome live semi-independent lives, with an average life expectancy of 56 in the United States (Eyman et al., 1991). Aneuploidies such as Down syndrome can generally be detected by the presence of additional chromosomes or chromosome translocations in akaryotype or FISH profile.
Single-Gene Defects
As opposed to chromosomal abnormalities, single-gene defects are usually inherited. For example, phenylketonuria (PKU) is a heritable condition caused by the malfunction of the PAH enzyme that breaks down the amino acid phenylalanine. Because this enzyme is coded for by the PAH gene onchromosome 12, PKU falls under the category of single-gene defects.
Interestingly, many single-gene defects are variably prevalent among different racial and ethnic groups. For instance, sickle-cell anemia (a disorder of the hemoglobin) is most common among people of African, Indian, and Mediterranean descent, whereas Tay-Sachs and Sandhoff diseases (both of which affect the nervous system) occur most frequently among Ashkenazi Jews. Tay-Sachs and Sandhoff diseases are both caused by a lack of the proteinhexosaminidase, which controls the levels of fatty buildup in the brain. Specifically, autosomal recessive mutations in the HEXA gene on chromosome 15 cause various forms of Tay-Sachs, while the presence of a mutated HEXB gene on chromosome 5 causes Sandhoff. These disorders mainly affect young children, who typically die during the first few years of life from progressive neural degeneration.
Multifactorial Influences
In certain cases, a combination of genetic mutations and teratogens leads to the development of multifactorial birth defects.
Although the exact causes of most multifactorial disorders are poorly understood, doctors can often identify common trends among similar conditions. Folate deficiency, for example, appears to play a role in various malformations of the neural tube, but the cumulative causes of such malformations and their relative contribution are rather complex. Neural tube defects have also been linked to trisomy 18, numerous mutations in the genes necessary for the development of the nervous system, and exposure to certain epilepsy drugs. Of the different forms of neural tube defects, a condition known as anencephaly is arguably the most severe. Anencephalic babies lack most of their brain and are often stillborn or die soon after birth. Spina bifida is a (relatively) less severe defect of the neural tube characterized by a series of deformities that are associated with incomplete enclosure of the spinal cord by the twenty-eighth day of development. The exposed spinal cord and the surrounding tissues are usually sealed surgically soon after birth, but the neurological effects, including partial paralysis and loss of bladder control, often last a
lifetime.
Of course, not all birth defects have such profound consequences. Consider, for example, cleft lip and palate; this is a multifactorial birth defect that, if left uncorrected, can create difficulties with eating and speech. Children born with cleft lip usually undergo corrective surgery at an early age. Although genes definitely play a role in the development of this defect, environmental factors, including smoking and the use of antiseizure drugs, have been associated with a greater risk of bearing a child with cleft lip and/or palate (Ericson et al., 1979; Knight & Rhind, 1975).
Prenatal Environment
It is difficult to overemphasize the importance of prenatal environment to a developing fetus. Indeed, a pregnant mother's health, diet, and level of exposure to toxins and environmental pollutants all have a direct effect on fetal development. For example, one of the most highly publicized cases of widespread toxin exposure associated with a pronounced increase in birth defects involves the use of Agent Orange, an herbicide that contains the poison dioxin, by the U.S. Army during the Vietnam War. Since the end of that conflict, the frequency of birth defects in those areas exposed to dioxin has risen to almost three times the norm. Dioxin, a product of industrial processes, disrupts the function of nuclear receptors and interferes with cellsignaling. Moreover, dioxin is fat soluble and takes a long time to degrade, which means it can build up over time in soil, in water, and in the fatty tissue of animals that humans consume.
Other environmental toxins that might harm a fetus are taken voluntarily, such as drugs, alcohol, and cigarettes. For instance, excessive maternal alcohol consumption often causes fetal alcohol syndrome, which is characterized by defects of major organs, abnormal facial features, and mental retardation. Similarly, smoking during pregnancy has been linked to an increased risk of stillbirths, low birth weights, and cleft lip and/or palate (Ericson et al., 1979; Knight & Rhind, 1975). Although studies have not demonstrated a strong correlative link between a high incidence of birth defects and consumption of moderate amounts of alcohol and tobacco, doctors strongly recommend complete abstinence from smoking and drinking during pregnancy.
Yet another major factor linked to abnormal prenatal development is poor diet during pregnancy. Certain foods, such as seafood with high mercury content, should be consumed in moderation, whereas other high-vitamin foods are encouraged. Dietary supplements, such as folate (vitamin B9) and iodine taken before and during the early stages of pregnancy, can aid in development of the neural tube. It is important to understand, however, that good diet and a healthy lifestyle do not ensure a healthy child, although they do play a protective role in certain individuals.
Limiting the Frequency of Birth Defects
Although some congenital defects cannot be prevented, improvements in health care, nutrition, and education can reduce their frequency and phenotypic severity. The increasing use of prenatal genetic screens and preimplantation genetic diagnosis (PGD) is also helping limit the frequency and the severity of birth defects. These advances are a great tool, but they also have a surprising downside. Specifically, deleterious genetic mutations that have a recessive pattern of inheritance will remain in the population if the parents seeking PGD are allowed to select only healthy embryos to be carried to term. The current use of this technique, however, is limited to the select few who can afford it, so this phenomenon will not have a noticeable impact on the overall population for quite some time.
|What is a birth defect? |
| |
| |
| |
| |
|A "birth defect" is a health problem or physical change, which is present in a baby at |
|the time he/she is born. Birth defects may be very mild where the baby looks and acts |
|like any other baby, or birth defects may be very severe, where you can immediately |
|tell there is a health problem present. Some of the severe birth defects can be life |
|threatening, where a baby may only live a few months, or may die at a young age (in |
|their teens, for example). |
| |
|Birth defects are also called "congenital anomalies" or "congenital abnormalities." The|
|word "congenital" means "present at birth." The words "anomalies" and "abnormalities" |
|mean that there is a problem present in a baby. |
|[pic] | |
| |How frequently do birth defects occur? |
|[pic] |Most babies are born healthy. In fact, 96 to 97 out of every 100 babies |
| |born is born healthy. About three or four out of every 100 babies born, |
| |however, has some type of birth defect. |
|[pic] | |
| |What causes birth defects to occur? |
|[pic] |There are many reasons why birth defects happen. Most occur due to |
| |environmental and genetic factors. About 40 percent of all birth defects|
| |have a known cause. The remaining 60 percent of birth defects do not |
| |have a known cause. You may find it surprising that scientists and |
| |physicians have not determined the cause for all birth defects. This is |
| |why there is a lot of research into the causes of birth defects, to |
| |understand more about why they happen and how to prevent them. |
|[pic] | |
| |Who is affected by birth defects? |
|[pic] |Birth defects have been present in babies from all over the world, in |
| |families of all nationalities and backgrounds. Anytime a couple becomes |
| |pregnant, there is a chance that their baby will have a birth defect. As|
| |mentioned above, this chance is three to four out of 100, or 3 to 4 |
| |percent. This means that there is a 96 to 97 percent chance with each |
| |pregnancy, for a baby to be born normal and healthy. The "3 to 4 |
| |percent" number is sometimes called the "background rate for birth |
| |defects" or the "population risk for birth defects." |
| | |
| |In a family where birth defects are already present, the chance for a |
| |couple to have a child with a birth defect may be higher than the |
| |background rate of 3 to 4 percent. |
|[pic] | |
| |What are the genetic and environmental causes of birth defects? |
|[pic] |When a baby is born with a birth defect, the first question usually |
| |asked by the parents is "how did this happen?" Sometimes, this question |
| |cannot be answered. This can be very upsetting for parents because it is|
| |normal to search for and desire an answer as to why your baby has a |
| |health problem. For about 40 percent of birth defects, however, there is|
| |a known cause, which has to do with either genetic or environmental |
| |factors, or a combination of the two. Here is some general information |
| |and terms related to the different causes of birth defects: |
|[pic] | |
| |Inheritance - Inheritance is a word used to describe a trait given to |
| |you or "passed on" to you from one of your parents. Examples of |
| |inherited traits would be your eye color or blood type. |
| | |
| |Chromosome abnormalities - Chromosomes are stick-like structures in the |
| |center of each cell (called the nucleus) that contain your genes. |
| |Problems involving chromosome material cause about 6 percent of all |
| |birth defects. |
| | |
| |Single gene defects - A defect in a gene is seen in about 7.5 percent of|
| |all birth defects. Genes are what determine your traits. Sometimes, a |
| |child can inherit not only those genes responsible for their normal |
| |traits such as the color of their eyes, but also disease causing genes |
| |that result in a birth defect. |
| | |
| |Multifactorial inheritance - Multifactorial inheritance means that "many|
| |factors" (multifactorial) are involved in causing a birth defect. The |
| |factors are usually both genetic and environmental. About 20 percent of |
| |all birth defects are the result of multifactorial inheritance. |
| |Teratogens - A teratogen is an agent, which can cause a birth defect. It|
| |is usually something in the environment that the mother may be exposed |
| |to during her pregnancy. It could be a prescribed medication, a street |
| |drug, alcohol use, or a disease that the mother has, which could |
| |increase the chance for the baby to be born with a birth defect. About 4|
| |to 5 percent of birth defects are caused by exposure to a teratogen. |
Like most expectant parents, you probably alternate between fantasies about a healthy baby and worries that your baby will have a health problem. Or perhaps you've been told throughprenatal screening that your baby might be born with a birth defect.
Many parents assume that all birth defects are severe or even fatal, but the fact is that many are treatable, often immediately after birth — and sometimes even before the baby is born.
It's especially important to know the risk factors involved and how to prevent birth defects. However, it's also important to realize that most babies born with congenital defects are born to two healthy parents.
About Birth Defects
Birth defects are defined as abnormalities of structure, …show more content…
function, or body metabolism that are present at birth. Major birth defects are abnormalities that lead to developmental or physical disabilities or require medical or surgical treatment. There are more than 4,000 different known birth defects, ranging from minor to serious, and although many can be treated or cured, they're the leading cause of death in the first year of life.
According to the March of Dimes, about 150,000 babies are born with birth defects each year in the United States. The American College of Obstetricians and Gynecologists (ACOG) says that 3 out of every 100 babies born in the United States have some kind of major birth defect.
Birth defects can be caused by genetic, environmental, or unknown factors. For most birth defects, the cause is believed to be an interaction of a number of genetic and environmental factors.
Structural or metabolic defects are those in which a specific body part is missing or formed incorrectly; metabolic birth defects are those in which there is an inborn problem in body chemistry. The most common type of major structural defects are heart defects, which affect 1 in 150 babies in the United States.
Other common structural defects include spina bifida, cleft palate, clubfoot, and congenital dislocated hip.
Metabolic defects affect 1 in 3,500 babies and usually involve a missing or incorrectly formed enzyme (a protein necessary for processing chemical substances in the body). Most children with a metabolic birth defect do not have any visible abnormalities, but metabolic defects are usually harmful or can be even fatal. Metabolic defects include Tay-Sachs disease, a fatal disease that affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein.
Defects caused by congenital infections result when a mother gets an infection before or during the pregnancy.
Infections that can cause birth defects include rubella (German measles),cytomegalovirus (CMV), syphilis, toxoplasmosis, Venezuelan equine encephalitis, parvovirus, and, rarely, chickenpox. None of these affect 100% of babies whose mothers are infected during pregnancy. If the mother is infected during early pregnancy, rubella carries the highest risk for birth defects (approximately 20%). Because of nearly universal immunization in the United States, rubella is very, very rare and the congenital rubella syndrome is almost never seen. CMV is probably the most common congenital infection and may be associated with intellectual disability (mental retardation) and hearing …show more content…
loss.
Other causes of birth defects include alcohol abuse by the mother. Although a few medications, such as medicines used for epilepsy, are associated with increased risks for certain birth defects, most commonly prescribed drugs are not associated with a significant risk of birth defects.
Birth Defects: Causes and Statistics
By: Ingrid Lobo, Ph.D. (Write Science Right) & Kira Zhaurova, M.S. (Nature Education) © 2008 Nature Education
Citation: Lobo, I. & Zhaurova, K. (2008) Birth defects: causes and statistics. Nature Education 1(1)
Every year, about 7.9 million infants (6% of worldwide births) are born with serious birth defects. With the causes of over 50% of birth defects unknown, how do we diagnose and prevent them?
Every year, an estimated 7.9 million infants (6% of worldwide births) are born with serious birth defects. Although some congenital defects can be controlled and treated, an estimated 3.2 million of these children are disabled for life. Moreover, birth defects are the leading cause of infant mortality in the United States. But where do these defects come from? Although some birth defects are inherited, others are a product of harmful environmental factors known as teratogens, and still others are multifactorial, resulting from a complex interaction of genetic and environmental influences. However, in approximately half of all birth defect cases, the causes are unknown (Christianson et al., 2006).
Genetic causes of birth defects fall into three general categories: chromosomal abnormalities, single-gene defects, and multifactorial influences. Prenatalenvironment can play a major role in the development of defects in all three categories, especially those linked to multifactorial causes.
Chromosomal Abnormalities
A person's genetic makeup is determined at conception. It is then, during the nuclear events of fertilization, that the genetic causes of many birth defects are determined. For example, chromosomal abnormalities, or large-scale duplications or deletions of chromosomal segments or entire chromosomes, can become apparent during this period. Many zygotes that carry such abnormalities do not develop into embryos, but among those that are carried to term,trisomy 21 (Down syndrome), trisomy 13 (Patau syndrome), and trisomy 18 (Edwards syndrome) are the most frequent birth defects. Embryos with these three conditions will develop severe disabilities regardless of the environmental factors associated with the pregnancy.
Unlike Down syndrome patients, who usually have a relatively long life span, children with Patau and Edwards syndromes often die soon after birth (March of Dimes, 2006). Individuals diagnosed with Patau syndrome suffer from neurological problems, mental and motor deficiencies, and polydactyly (Figure 1), as well as eye, heart, and spine defects (Patau et al., 1960). Those born with Edwards syndrome suffer mental retardation, breathing and feeding difficulties, delayed growth, and malformations of the kidneys, intestines, and heart (Edwards et al., 1960; Van Dyke & Allen, 1990). Thankfully, both of these devastating syndromes are rare.
Figure 2: Primary Down syndrome is caused by the presence of three copies of chromosome 21.
(a) A child who has Down syndrome. (b) Idiogram of a person who has primary Down syndrome.
Copyright National Institutes of Health.
Down syndrome, on the other hand, is by far the most common chromosomal abnormality, affecting 1 in 800 babies. The risk of having a child with this condition increases with maternal age, rising exponentially after a woman reaches age 35. For instance, in young mothers, the frequency of trisomy 21is about 1 in 2,000, but this frequency rises to 1 in 100 when a woman is 40 and to 1 in 12 when she is 50 years old (Figure 2). People who have Down syndrome suffer from moderate to severe mental retardation and a wide variety of health problems, including heart defects, leukemia, and Alzheimer'sdisease. The severity of these defects varies widely, however, and the majority of people with Down syndrome live semi-independent lives, with an average life expectancy of 56 in the United States (Eyman et al., 1991). Aneuploidies such as Down syndrome can generally be detected by the presence of additional chromosomes or chromosome translocations in akaryotype or FISH profile.
Single-Gene Defects
As opposed to chromosomal abnormalities, single-gene defects are usually inherited. For example, phenylketonuria (PKU) is a heritable condition caused by the malfunction of the PAH enzyme that breaks down the amino acid phenylalanine. Because this enzyme is coded for by the PAH gene onchromosome 12, PKU falls under the category of single-gene defects.
Interestingly, many single-gene defects are variably prevalent among different racial and ethnic groups. For instance, sickle-cell anemia (a disorder of the hemoglobin) is most common among people of African, Indian, and Mediterranean descent, whereas Tay-Sachs and Sandhoff diseases (both of which affect the nervous system) occur most frequently among Ashkenazi Jews. Tay-Sachs and Sandhoff diseases are both caused by a lack of the proteinhexosaminidase, which controls the levels of fatty buildup in the brain. Specifically, autosomal recessive mutations in the HEXA gene on chromosome 15 cause various forms of Tay-Sachs, while the presence of a mutated HEXB gene on chromosome 5 causes Sandhoff. These disorders mainly affect young children, who typically die during the first few years of life from progressive neural degeneration.
Multifactorial Influences
In certain cases, a combination of genetic mutations and teratogens leads to the development of multifactorial birth defects.
Although the exact causes of most multifactorial disorders are poorly understood, doctors can often identify common trends among similar conditions. Folate deficiency, for example, appears to play a role in various malformations of the neural tube, but the cumulative causes of such malformations and their relative contribution are rather complex. Neural tube defects have also been linked to trisomy 18, numerous mutations in the genes necessary for the development of the nervous system, and exposure to certain epilepsy drugs. Of the different forms of neural tube defects, a condition known as anencephaly is arguably the most severe. Anencephalic babies lack most of their brain and are often stillborn or die soon after birth. Spina bifida is a (relatively) less severe defect of the neural tube characterized by a series of deformities that are associated with incomplete enclosure of the spinal cord by the twenty-eighth day of development. The exposed spinal cord and the surrounding tissues are usually sealed surgically soon after birth, but the neurological effects, including partial paralysis and loss of bladder control, often last a
lifetime.
Of course, not all birth defects have such profound consequences. Consider, for example, cleft lip and palate; this is a multifactorial birth defect that, if left uncorrected, can create difficulties with eating and speech. Children born with cleft lip usually undergo corrective surgery at an early age. Although genes definitely play a role in the development of this defect, environmental factors, including smoking and the use of antiseizure drugs, have been associated with a greater risk of bearing a child with cleft lip and/or palate (Ericson et al., 1979; Knight & Rhind, 1975).
Prenatal Environment
It is difficult to overemphasize the importance of prenatal environment to a developing fetus. Indeed, a pregnant mother's health, diet, and level of exposure to toxins and environmental pollutants all have a direct effect on fetal development. For example, one of the most highly publicized cases of widespread toxin exposure associated with a pronounced increase in birth defects involves the use of Agent Orange, an herbicide that contains the poison dioxin, by the U.S. Army during the Vietnam War. Since the end of that conflict, the frequency of birth defects in those areas exposed to dioxin has risen to almost three times the norm. Dioxin, a product of industrial processes, disrupts the function of nuclear receptors and interferes with cellsignaling. Moreover, dioxin is fat soluble and takes a long time to degrade, which means it can build up over time in soil, in water, and in the fatty tissue of animals that humans consume.
Other environmental toxins that might harm a fetus are taken voluntarily, such as drugs, alcohol, and cigarettes. For instance, excessive maternal alcohol consumption often causes fetal alcohol syndrome, which is characterized by defects of major organs, abnormal facial features, and mental retardation. Similarly, smoking during pregnancy has been linked to an increased risk of stillbirths, low birth weights, and cleft lip and/or palate (Ericson et al., 1979; Knight & Rhind, 1975). Although studies have not demonstrated a strong correlative link between a high incidence of birth defects and consumption of moderate amounts of alcohol and tobacco, doctors strongly recommend complete abstinence from smoking and drinking during pregnancy.
Yet another major factor linked to abnormal prenatal development is poor diet during pregnancy. Certain foods, such as seafood with high mercury content, should be consumed in moderation, whereas other high-vitamin foods are encouraged. Dietary supplements, such as folate (vitamin B9) and iodine taken before and during the early stages of pregnancy, can aid in development of the neural tube. It is important to understand, however, that good diet and a healthy lifestyle do not ensure a healthy child, although they do play a protective role in certain individuals.
Limiting the Frequency of Birth Defects
Although some congenital defects cannot be prevented, improvements in health care, nutrition, and education can reduce their frequency and phenotypic severity. The increasing use of prenatal genetic screens and preimplantation genetic diagnosis (PGD) is also helping limit the frequency and the severity of birth defects. These advances are a great tool, but they also have a surprising downside. Specifically, deleterious genetic mutations that have a recessive pattern of inheritance will remain in the population if the parents seeking PGD are allowed to select only healthy embryos to be carried to term. The current use of this technique, however, is limited to the select few who can afford it, so this phenomenon will not have a noticeable impact on the overall population for quite some time.
|What is a birth defect? |
| |
| |
| |
| |
|A "birth defect" is a health problem or physical change, which is present in a baby at |
|the time he/she is born. Birth defects may be very mild where the baby looks and acts |
|like any other baby, or birth defects may be very severe, where you can immediately |
|tell there is a health problem present. Some of the severe birth defects can be life |
|threatening, where a baby may only live a few months, or may die at a young age (in |
|their teens, for example). |
| |
|Birth defects are also called "congenital anomalies" or "congenital abnormalities." The|
|word "congenital" means "present at birth." The words "anomalies" and "abnormalities" |
|mean that there is a problem present in a baby. |
|[pic] | |
| |How frequently do birth defects occur? |
|[pic] |Most babies are born healthy. In fact, 96 to 97 out of every 100 babies |
| |born is born healthy. About three or four out of every 100 babies born, |
| |however, has some type of birth defect. |
|[pic] | |
| |What causes birth defects to occur? |
|[pic] |There are many reasons why birth defects happen. Most occur due to |
| |environmental and genetic factors. About 40 percent of all birth defects|
| |have a known cause. The remaining 60 percent of birth defects do not |
| |have a known cause. You may find it surprising that scientists and |
| |physicians have not determined the cause for all birth defects. This is |
| |why there is a lot of research into the causes of birth defects, to |
| |understand more about why they happen and how to prevent them. |
|[pic] | |
| |Who is affected by birth defects? |
|[pic] |Birth defects have been present in babies from all over the world, in |
| |families of all nationalities and backgrounds. Anytime a couple becomes |
| |pregnant, there is a chance that their baby will have a birth defect. As|
| |mentioned above, this chance is three to four out of 100, or 3 to 4 |
| |percent. This means that there is a 96 to 97 percent chance with each |
| |pregnancy, for a baby to be born normal and healthy. The "3 to 4 |
| |percent" number is sometimes called the "background rate for birth |
| |defects" or the "population risk for birth defects." |
| | |
| |In a family where birth defects are already present, the chance for a |
| |couple to have a child with a birth defect may be higher than the |
| |background rate of 3 to 4 percent. |
|[pic] | |
| |What are the genetic and environmental causes of birth defects? |
|[pic] |When a baby is born with a birth defect, the first question usually |
| |asked by the parents is "how did this happen?" Sometimes, this question |
| |cannot be answered. This can be very upsetting for parents because it is|
| |normal to search for and desire an answer as to why your baby has a |
| |health problem. For about 40 percent of birth defects, however, there is|
| |a known cause, which has to do with either genetic or environmental |
| |factors, or a combination of the two. Here is some general information |
| |and terms related to the different causes of birth defects: |
|[pic] | |
| |Inheritance - Inheritance is a word used to describe a trait given to |
| |you or "passed on" to you from one of your parents. Examples of |
| |inherited traits would be your eye color or blood type. |
| | |
| |Chromosome abnormalities - Chromosomes are stick-like structures in the |
| |center of each cell (called the nucleus) that contain your genes. |
| |Problems involving chromosome material cause about 6 percent of all |
| |birth defects. |
| | |
| |Single gene defects - A defect in a gene is seen in about 7.5 percent of|
| |all birth defects. Genes are what determine your traits. Sometimes, a |
| |child can inherit not only those genes responsible for their normal |
| |traits such as the color of their eyes, but also disease causing genes |
| |that result in a birth defect. |
| | |
| |Multifactorial inheritance - Multifactorial inheritance means that "many|
| |factors" (multifactorial) are involved in causing a birth defect. The |
| |factors are usually both genetic and environmental. About 20 percent of |
| |all birth defects are the result of multifactorial inheritance. |
| |Teratogens - A teratogen is an agent, which can cause a birth defect. It|
| |is usually something in the environment that the mother may be exposed |
| |to during her pregnancy. It could be a prescribed medication, a street |
| |drug, alcohol use, or a disease that the mother has, which could |
| |increase the chance for the baby to be born with a birth defect. About 4|
| |to 5 percent of birth defects are caused by exposure to a teratogen. |