Birth Defects

Birth Defects Ratio Introduction: 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. 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. 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. Twenty per cent or more of malformed foetuses are spontaneously aborted; the rest result in babies with birth abnormalities. Although each single type of birth abnormality is rare, taken together they make up almost 5 per cent of all live births and cause about 20 per cent of infant deaths in the period immediately after birth. About one in ten developmental disorders is hereditary and arises from an abnormality in a single gene. Another 5 per cent of birth abnormalities arise from physical abnormalities in the chromosome. 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"(Greek,teratos,monster;gene,born) 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. 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. 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 alphafetoprotein (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.

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.

Review of literature Birth defects or congenital malformations are inborn structural abnormalities of organs or body parts. The frequency is by definition measured as prevalence at the time of birth and occurs in 3.5% of all live births. Severe malformations which are incompatible with foetal growth and do not survive to birth are not included in birth defect. Data on spontaneous abortion may be important for the detection of teratogenic factors [1]. Severe malformations may end in very early loss of conceptions that do not survive to clinical recognition and are never detected. Screening during pregnancy and improved medical technology, such as ultrasound and genetic methods, make it possible to detect some birth defects at an early stage, which may lead to induced abortion and affect the prevalence of birth defects. In exposure of the foetus through the mother, the teratogenic effect may arise during the organogenesis phase, and in humans the most vulnerable period is the first 3–8 weeks of pregnancy. In this period, the three germ layers give rise to tissues and organs. Certain birth defects can come into existence after the critical period as well. It seems plausible that different types of structural malformations may share biological mechanisms and that a given teratogenic factor may cause several types of malformations depending on the time window and level of exposure. Most known human teratogens seem to cause specific birth defects [2]. A large percentage of the workforce consists of women and a considerable proportion are of reproductive age. Nearly 70% of all birth defects have no known risk factors, therefore attention to the risk of birth defects due to occupational exposure could be of great interest. Several reviews have addressed birth defects related to limited exposures, such as pesticides [3,4], glycol ethers [5] and inhalation anaesthetics [6], while others have included the entire range of diverse occupational settings and exposures [7–8]. In 1994, Sever [8] concluded that epidemiological research had not convincingly established an association between workplace exposure as a human teratogen and birth defects, but since then a large body of literature has suggested that organic solvents, pesticides and some heavy metals may be involved in the causation of birth defects in humans [3–6,8]. Specific birth defects are seen following pharmaceutical exposures such as limb defects related to thalidomide, genital anomalies linked to diethylstilbestrol, spina bifida linked to valproic acid, oral clefts related to phenytoin and vitamin A causing neural crest defects [5,9–10]. However, although the overall prevalence did not change significantly, a greater prevalence of birth defects among infants of low birthweight and preterm gestation might signal a need for increased prenatal health care and planning for the extended-care requirements. The greater prevalence of defects among the offspring of women aged 35 years likely reflects an upward trend in maternal age distribution and the progressive association of certain defects as maternal age increases beyond 35 years.11-12

Major birth defects also represent a global public health burden. A recent report by the March of Dimes showed that, worldwide, an estimated 6% of births or 7.9 million children are born annually with a major birth defect of genetic or partially genetic origin. Among the most common disorders identified were congenital heart defects, neural tube defects, thalassemia, sickle cell disease, Down syndrome, and glucose-6-phosphate dehydrogenase deficiency. The report also cited that, annually, hundreds of thousands more children are born with defects resulting from in utero exposure to teratogenic agents, such as alcohol or infectious disease, and that at least 3.3 million children <5 years old die as a result of major birth defects. The highest totals of occurrence (94%) and deaths (95%) that resulted from major birth defects were found in middle- and low-income countries.[13 ]

For the pediatric patient, birth defects exemplify such multifactorial conditions. Birth defects can be grouped into 2 broad categories: major and minor defects. A major defect is an abnormality of an organ structure or function that results in physical disability, mental disability, or death,[13] whereas a minor defect does not produce significant health consequences.[14] Both major and minor defects can occur as isolated entities, affecting 1 organ system, or as multiple defects, affecting 1 or several organ systems. Alone, minor defects are not considered to have significant health consequences, although their presentation with 1 or more major defects can provide clues to an underlying genetic or teratogenic etiology. Conservatively, estimates suggest that a causal gene or teratogen accounts for <30% of defects that occur. For the remainder, the most likely explanation is a confluence of genetic and teratogenic exposures and, to a lesser degree, factors such as intrauterine constraint and amniotic bands that can lead to deformations and disruptions, respectively, of otherwise normally developed structures.[14]

As with many common chronic diseases, multiple etiologies for major birth defects present challenges in disentangling risk associated with a reported family history of these conditions. Approaches to inferring risk of common chronic diseases on the basis of family history information have been attempted through calculation of quantitative family history scores[15] or classification of risk into qualitative categories.[16]

In the United States, major birth defects, including structural defects and chromosome anomalies, are estimated to affect 3% of all live births.[17] Major birth defects also continue to be the leading cause of infant mortality in the United States,[18] and costs for care and treatment of children with major birth defects annually totals millions of dollars.[19] Canfield et al[17] used pooled data from 11 states with active case finding to calculate national birth prevalence estimates for 18 selected defects. Rates calculated ranged from 0.82 per 10000 live births for truncus arteriosis to 13.65 per 10000 live births for Down syndrome, and these estimates varied according to race and ethnicity. Compared with the rates for children of non-Hispanic white mothers, rates were significantly higher for tetralogy of Fallot, lower-limb–reduction defects, and trisomy 18 among children of non-Hispanic black mothers and significantly higher for anencephalus, spina bifida, encephalocele, gastroschisis, and Down syndrome among children of Hispanic mothers.

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A. Correa, J. Cragan and CJ.2004.Alverson. Prenatal diagnosis, pregnancy terminations and prevalence of Down syndrome in Atlanta. Birth Defects Res A Clin Mol Teratol;70(9):565-571. 13. Christianson A, CP. Howson, B. Modell; March of Dimes Birth Defects Foundation. Executive Summary: March of Dimes Global Report on Birth Defects—The Hidden Toll of Dying and Disabled Children. White Plains, NY: March of Dimes Birth Defects Foundation; 2006. Report No. 31-200905. Available at: http://mod.hoffmanpr.com/MOD-ExecutiveSummary.pdf. Accessed June 13, 2007 6. Falk MJ, NH. Robin. 2004. The primary care physician's approach to congenital anomalies. Prim Care;31 :605 –619.

7. Hunt SC, RR. Williams and GK. Barlow. A comparison of positive family history definitions for defining risk of future disease [published correction appears in J Chronic Dis. 1987;40:369]. J Chronic Dis. 1986;39 :809 –821. 8. Scheuner MT, SJ. Wang, LJ. Raffel, SK. Larabell and JI. Rotter.1997. Family history: a comprehensive genetic risk assessment method for the chronic conditions of adulthood. Am J Med Genet;71 :315 –324 10. Canfield MA, MA. Honein, N. Yuskiv, et al.2006. National estimates and race/ethnic-specific variation of selected birth defects in the United States, 1999–2001. Birth Defects Res A Clin Mol Teratol;76 :747 –756 11. Petrini J, K. Damus, R. Russell, K. Poschman, M. Davidoff, D. Mattison.2002. Contribution of birth defects to infant mortality in the United States. Teratology;66(suppl 1) :S3 –S6 12. Waitzman NJ, RM. Scheffler, PS. Romano.1996. The Cost of Birth Defects: Estimates of the Value of Protection. Lanham, MD: University Press of America;