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Birth defects

Birth defects

10/10/2019
Posted by:

J.Phillips


Disclaimer: It has been brought to our attention that some physicians may view this article as an aggressive fear-marketing tactic. While we reject those claims, we feel it is important for readers of this article to know that such an opinion has been expressed. It is our view that expecting mothers, and for that matter all Canadians, have a right to make informed decisions about their healthcare. All information contained in this article is publicly available, and statistics are referenced from Congenital Anomalies in Canada 2013: A Perinatal Health Surveillance Report. This is the most recent report from the Canadian Perinatal Surveillance System (CPSS) dedicated to birth defects, the focus of this article. Further, this article was not written with the intent to promote any sales by Merogenomics. While Merogenomics is an advocate of non-invasive prenatal screening for pregnant women, such DNA test would screen for only a portion of the potential birth defects discussed in this article. We still stand by the value of non-invasive prenatal screening, and we stand by the notion that expecting mothers have the right to be informed about the types of risks that may come up during pregnancy. Out of respect to those who have complained, Merogenomics has stopped all marketing of this article, and will refrain from doing so in the future.

 

What are birth defects?

Birth defects are disabilities and disorders that are present in an infant from the time of their birth. Not all birth defects are created equally however; they range from mild defects that can be treated easily or possibly not need treatment at all, to severe defects that could cause serious disability or even death if not treated soon after birth. One or multiple body systems could be affected with changes in the way the body looks, develops or functions. The Canadian government released a surveillance report on birth defects in 2013 that aimed to deepen our understanding and their prevalence in our nation.

Birth defects affect approximately 1 in 25 newborns each year. While the rate of birth defects has decreased over the years, there has also been a simultaneous increase in the rate of stillbirths. This rise in rate of stillbirths may reasonably be explained by the rise in the number of pregnancy terminations linked to birth defects. In addition to lifelong morbidity, many birth defects are associated with significant mortality. Defects of the heart, lungs, brain, and genetics make up a considerable portion of the 1 in 5 newborn deaths that result from birth defects.

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For families, birth defects mean a future of significant emotional, psychological, and financial burdens. Upon learning about a diagnosis, families grieve the loss of the healthy baby they once expected to take home while also preparing for the uncertainty that comes with raising a child with a disability. For society, birth defects come with a significant cost as affected individuals and their families need emotional, financial, and medical resources to help them manage lifelong morbidity.

Since birth defects have such a profound impact on both the lives of families and society as a whole, it makes sense that a lot of effort is focused on treatment and prevention. Understanding these health issues is therefore an important first step towards reducing the impact these conditions have on the lives of Canadians.

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The cause of some birth defects can be easily determined, such as those that come from genetic errors in a single gene or chromosome; however, the cause of many others is multifactorial. In other words, most birth defects are the result of an interaction between an embryo’s genes (the DNA they inherit from their parents) and the environment of the uterus they develop in. Ultimately this means that there are many risk factors that influence the likelihood of having a baby with a birth defect. This article will look at some of the most common risk factors that are associated with birth defects and some of the most common birth defects affecting families today.

Stay tuned for a follow-up article that will detail some prevention strategies that can help decrease the prevalence of birth defects.

 

What causes birth defects?

Understanding birth defects and what causes them is a key first step in being able to treat and prevent them. While the cause of most birth defects remains largely unknown, there are some factors that increase the chances of having a baby with a birth defect. These factors that increase the risk of having an affected pregnancy are called risk factors.

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One of the most well-established risk factors is someone’s genetics, particularly if they have previously had an affected pregnancy or if birth defects run in their family. Some birth defects are caused by the inheritance of mutations within a single gene, like the metabolic disease phenylketonuria (commonly called PKU) which affects the body’s ability to digest the amino acid phenylalanine. For single gene disorders like this, understanding your chances of passing this disorder onto your child, or your risk, can be calculated rather simply with the help of a genetic counsellor.

Unfortunately, most birth defects that are influenced by your genetics are not single gene disorders. These disorders that are influenced by a combination of genetic predisposition and environment are called multifactorial or complex disorders. The environment of the uterus is influenced by what a mother is exposed to during pregnancy as well as certain medical conditions she may have. It is important to maintain a healthy uterine environment for the entire pregnancy. While most birth defects come about during the first trimester (the first three months of pregnancy), a baby’s organs continue to develop and grow throughout the pregnancy and therefore a birth defect can occur at any time.

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Risk factors for birth defects

  • Alcohol Use: The use of alcohol during pregnancy has many well documented effects on the fetus. The spectrum of birth defects caused by alcohol exposure is called Fetal Alcohol Spectrum Disorder (FASD) and is characterized by impaired growth, cognition, and effects on a child’s behaviour and physical appearance. Alcohol use is one of the leading causes of preventable birth defects and intellectual handicap.
  • Cigarette Smoking: In addition to the known health risks for smokers, smoking while pregnant increases the risk of having a baby with defects in their cardiovascular system, muscoskeletal system, gastrointestinal system, or a cleft lip or cleft palate (collectively called orofacial clefts).
  • Medications: The effect of many medications on pregnancy has not yet been documented and therefore the safest option when pregnant is to take the fewest medications possible. Some medications used to treat epilepsy, such as valproic acid and carbamazepine, are associated with increased risk for some birth defects that affect the brain, spine and/or spinal cord, collectively called neural tube defects. Similarly, the drug thalidomide which is used to treat leprosy and certain cancers is linked with limb deficiency defects, a class of defects where parts of or whole limbs are missing. Another medication called isotretinoin, commonly known as the acne treating drug Accutane, is associated with brain, heart, and facial deformities.
  • Recreational Drugs: Drugs like marijuana and cocaine have been linked with premature birth and low birth weight, childhood developmental and behavioural issues, increased risk for a type of childhood cancer called neuroblastoma, and the birth defect gastroschisis, a defect where a baby’s intestines exit the body through a hole in the belly.
  • Infections: Certain infections in the mother have the ability to negatively affect the development of a baby. For example, the Zika virus is associated with severe brain defects including microcephaly, a defect characterized by a smaller than normal head. The effect of other infections such as rubella or toxoplasmosis can vary depending on which organs are developing at the time of infection. Birth defects from infections can be severe and have lifelong consequences, or even cause a miscarriage or stillbirth.
  • Maternal Age: The age of a woman when she gets pregnant influences the risk for certain birth defects. Chromosome disorders such as Down syndrome are more likely for mothers over the age of 34. Becoming pregnant at a young age has risks as well, as very young mothers are more likely to have a baby with gastroschisis.
  • Poor Nutrition: It is well established that good nutrition is necessary for fetal development and for a healthy pregnancy overall. Studies have shown that taking multivitamin supplements during pregnancy reduces the risk of various birth defects including neural tube defects, congenital heart defects, orofacial clefts, and limb deficiency defects, among others. Research on the effects of folic acid have shown that deficiencies of this key nutrient during pregnancy are clearly and consistently linked with the development of neural tube defects.
  • Obesity: High BMIs (Body Mass Indexes) are significantly associated with an increased risk for neural tube defects as well as some congenital heart defects. Obesity is also a risk factor for other birth defects including orofacial clefts, hydrocephalus (a buildup of fluid in the brain), anorectal atresia (a condition where the digestive tract fails to empty to outside of the body because the anus has not developed), and limb deficiency defects. Research suggests the level of risk is influenced by the severity of obesity. While other risk factors like diabetes are often associated with obesity, it is generally accepted that obesity is an independent risk factor.
  • Diabetes: Diabetes is a medical condition that affects blood sugar levels. Uncontrolled diabetes during pregnancy can lead to many different birth defects including neural tube defects, congenital heart defects, and limb deficiency defects, among others.
  • Environmental Exposures: The environment that a mother is exposed to during pregnancy has the potential to affect the uterine environment for her baby. Some research suggests that exposure to hazards like land waste sites, poor air quality, pesticides, or occupational exposure to other chemicals during pregnancy can potentially increase the risk for low birth weight, certain types of cancers and some birth defects.

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  • Socioeconomic Status (SES): One’s SES is determined by many interrelated factors including education, occupation, and income. Compared to higher SES, low SES is associated with worse health outcomes and is a well-established risk factor for premature birth, low birth weight, miscarriages, stillbirths, and infant mortality. Many of the risk factors listed above are more common in lower social and economic classes including poor nutrition, obesity, cigarette and alcohol use, and hazardous environmental exposures. For example, lower housing prices means people in lower classes are more likely to live near landfills or other near potentially harmful pollutants. Even after adjusting for these other risk factors low SES has been shown to be an independent risk factor for certain congenital heart defects like transposition of the great arteries, a serious heart defect that can be fatal if not corrected soon after birth. Additionally, access to prenatal screening and diagnosis varies based on social status and is reflected in the rates of birth defect associated pregnancy termination.

 

What are Some Common Birth Defects?

Down Syndrome

Down syndrome is a genetic disorder caused by the presence of an extra chromosome 21. It is among the most common birth defects worldwide. In Canada, it has a birth prevalence of 1 in 800 births. Children born with Down syndrome will display a well-defined set of characteristics including short stature, distinct facial features, intellectual delay, and additional related health issues. Congenital heart defects and gastrointestinal defects are common and must be monitored. Individuals with Down syndrome have a shorter life expectancy due to the relatively high rates of heart defects, respiratory infections, and childhood leukemia.

Monitoring potential health risks and early intervention has improved the quality of care for people with Down syndrome, extending their life expectancy, decreasing morbidity, and improving their overall quality of life. The extent of disability is quite variable among those with Down syndrome, ranging from some who are nonverbal and have severe intellectual delay to others who are highly functional and take part in the workforce and normal social activities. While the level of support required can vary between cases, in the absence of severe additional defects, much of raising a child with Down syndrome is the same as raising any other child.

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Neural Tube Defects

Neural tube defects (NTDs) are a class of structural defects that result from a failure of the brain, spine, and/or spinal cord to form properly during development. The most common NTDs are spina bifida (characterized by a defect involving the spinal cord and surrounding spinal vertebrae), encephalocele (characterized by a sac of brain matter herniated through an opening in the skull), and anencephaly (characterized by an absence of skull, scalp, and brain matter). Of the three, spina bifida is the most common defect while anencephaly is the most serious. Babies born with anencephaly do not survive.

Spina bifida is considered to be among the most complex survivable birth defects. In this defect the spinal cord, which is responsible for sending signals back and forth between the brain and body, is compromised. It is not unusual for babies born with this condition to require surgery or other urgent treatment soon after birth. Depending on the severity of the defect, people with this condition experience considerable lifelong morbidity including brain complications, decreased mobility, bladder and bowel issues, and learning disabilities. Spina bifida also has social consequences related to peer acceptance and accessibility issues.

NTDs can be a result of chromosome disorders, genetic disorders, or environmental exposures. These malformations sometimes occur alongside other birth defects, however most cases of NTDs are isolated and the result of a multifactorial interaction between genetic predisposition and environment. The most well-established risk factor for NTDs is folate deficiency. Since this discovery, public health strategies surrounding this critical nutrient have decreased the prevalence of NTDs significantly, although higher rates of NTDs persist among populations with lower socioeconomic status.

 

Congenital Heart Defects

Congenital heart defects (CHDs) are a class of birth defects affecting the structure and/or function of the heart. Birth prevalence ranges from 50 to 150 per 10,000 total births (meaning live births and stillbirths), making it the most common birth defect and a major cause of disability and death for newborns and youth. Many babies with CHDs require surgery or other life-saving treatment within their first year.

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There are many different types of CHDs, and likewise there are many different causes of these birth defects. Some CHDs have been associated with genetic disorders. For instance, approximately 45% of individuals with Down syndrome will also have a CHD. Other chromosome disorders including DiGeorge syndrome and Williams-Beuren syndrome, as well as single gene disorders such as Alagille syndrome and Holt-Oram syndrome have been associated with higher rates of CHDs. However, CHDs can also occur independently of a diagnosable genetic disease. Other known risk factors for CHDs include maternal diabetes, rubella infection during pregnancy, as well as some medications such as anti-epileptics, lithium, and isotretinoin.

 

Orofacial Clefts

Birth defects involving a baby’s lip or mouth, such as cleft lip and cleft palate, are called orofacial clefts. Every year in Canada there are approximately 600 babies born with these types of birth defects. Due to the different mechanisms by which they arise, orofacial clefts are generally divided into isolated clefts of the secondary palate (CP) and cleft lips with or without clefting of the primary palate (CL+/-CP). The overall birth prevalence of orofacial clefts in Canada is about 16.3 per 10,000 total births, whereas the approximate prevalence of CL+/-CP and CP is 9.4 and 7.0, respectively. Surgery is generally needed in infancy to repair orofacial clefts. As children grow up they may need additional surgeries, speech therapy, and specialized dental care. Orofacial clefts often also come with psychological challenges resulting from stigmatization and lack of self-esteem. These issues are especially significant during school aged years but often continue into adulthood as well.

The specific cause of orofacial clefts remains a mystery, and therefore these types of birth defects continue to cause considerable morbidity and social consequences for affected individuals. About 70% of CL+/-CP cases and 50% of CP cases seem to be caused by an interaction between genetic predisposition and environment, whereas the rest of the cases are associated with various identifiable syndromes. Most orofacial clefts are therefore not associated with other additional birth defects.

Some risk factors have been identified as increasing the chance of having a baby with an orofacial cleft. The most significant risk factor is cigarette smoking while pregnant, which may increase risk by as much as 20%. Low socioeconomic status is another prominent risk factor. Studies in the UK have found the highest rates of orofacial clefts in communities with high concentrations of public housing, unemployment, and unskilled workers, while the lowest rates of orofacial clefts were found in wealthy communities with high concentrations of homeowners and professional, non-manual workers.

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Limb Deficiency Defects

Limb deficiency defects (LDDs) are a class of malformations that involve partial or complete absences of limb structures, such as an arm or a toe. These types of defects are highly variable. Amelia, the absence of a complete limb, is the most severe LDD. Malformations involving partial absences of limb structures are generally classified based on the missing segment. LDDs affect about 3 to 8 infants per 10,000 live births, and approximately 30% of these infants will also have additional birth defects. Mortality associated with LDDs is increased when other severe birth defects are present, such as heart defects.

Limb development is a complex process that involves multiple molecular signalling networks. This means there are many potential developmental pathways that can be interrupted, leading to the wide variety of LDDs. Disruptions in the network of associated blood vessels is the most common reason for LDDs to arise, however it’s still not clear exactly how this happens. Some studies suggest that early chorionic villus sampling (a method of prenatal genetic diagnosis) as well as conception using in vitro fertilization (an assisted reproduction technique sometimes referred to as “test-tube babies”) increase the risk for LDDs. These types of defects have also been associated with certain chromosome and single-gene disorders.

Many environmental exposures have been shown to increase risk including cigarette smoking, maternal diabetes, and some medications. These medications include the seizure medication valproic acid and the acne medication isotretinoin, but the most well-documented risk factor for LDDs is the medication thalidomide. In the late 50s and early 60s thalidomide was widely prescribed to pregnant women as an anti-nausea medication to help with morning sickness. As a result, over 10,000 children in almost 50 countries were born with various LDDs. Today use of thalidomide is restricted to the treatment of certain cancers and leprosy complications.

 

Gastroschisis

Gastroschisis is a birth defect in which a baby’s intestines, and occasionally other organs, exit the body through a hole in the belly. This hole in the abdominal wall occurs just beside the belly button and is a result of muscles of the abdomen failing to connect properly during development. This major defect needs to be surgically corrected soon after birth, however this is sometimes complicated if a baby’s abdominal cavity is too small to fit all of their intestines. These cases require an extended hospital stay as their organs will have to be inserted gradually back into the abdominal cavity.

Gastroschisis has a birth prevalence of about 3.7 per 10,000 total births. Recently many countries including Canada have experienced an increase in the rates of gastroschisis, though the reason for this increase it is still unknown. Generally, the presence of additional defects is considered rare, although there has been some research suggesting cases of multiple malformations often go unnoticed among the rates of stillbirths and infant mortality. Approximately 5% of babies with gastroschisis will not survive, and those that do often require long hospital stays and are at significant risk for intestinal failure.

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The exact cause of gastroschisis remains a mystery, although researchers believe one of the ways gastroschisis can happen involves a disruption in the network of associated blood vessels. Many risk factors have been associated with the occurrence of gastroschisis. Most consistently observed is the relationship between young maternal age and gastroschisis. Interestingly, young paternal age may be an independent risk factor as well. Other identified risk factors for gastroschisis include alcohol, nutritional deficiencies, exposure to herbicides, and infections of the genital area and urinary system.

One of the main goals of understanding birth defects and their associated risk factors is to use this information to help reduce the occurrence of birth defects and the degree of hardships that come with them. After reading this article, be sure to check out our follow-up article on prevention strategies that can help decrease the prevalence of birth defects.

 

This article has been produced by Jenna Phillips, B.Sc. Reproduction and reuse of any portion of this content requires Merogenomics Inc. permission and source acknowledgment. It is your responsibility to obtain additional permissions from the third party owners that might be cited by Merogenomics Inc. Merogenomics Inc. disclaims any responsibility for any use you make of content owned by third parties without their permission.

 

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