- Genetic disorders of the fetus
- Risk Factors for Genetic Disorders
- Types of Disorders
- Testing for Genetic Disorders
- Screening Tests
- Diagnostic Tests
- Genetic Counseling
- Treatment for Fetal Genetic Disorders
- The Benefits of Specialized Care
- Birth Defects: Causes, Definition & Types
- How common are birth defects?
- What are some other examples of birth defects?
- How do genes and chromosomes affect birth defects?
- How do environmental factors infection and drugs affect birth defects?
- How are birth defects diagnosed?
Genetic disorders of the fetus
Genetic disorders occur when a problem in the baby’s chromosomes or genes causes physical abnormalities or illnesses.
In our body, we have millions of cells. In each cell, there are 46 chromosomes, found in 23 matching pairs. Half of the chromosomes are passed on from a person’s mother, and half from their father. These chromosomes carry our DNA, or genes, which are the instructions for how we look and how our body develops and functions. These instructions range from our eye color to our risk for disease.
When a harmful change occurs in these instructions, it can change the way a baby develops. Babies with genetic disorders can be at risk of slow mental and physical development, physical abnormalities, and lifelong illnesses.
Some genetic disorders are hereditary, meaning the genetic change is passed on from their parents. Other genetic changes can happen for the first time in the baby. Parents can carry a change in a gene or a chromosome without realizing it, as it may not cause them any health problems.
Risk Factors for Genetic Disorders
Factors that increase your risk of having a baby with a genetic disorder include:
- Family history of a genetic disorder
- Prior child with a genetic disorder
- One parent has a chromosomal abnormality
- Advanced maternal age (35 or older)
- Advanced paternal age (40 or older)
- Multiple miscarriages or prior stillbirth
It is important to know that some birth defects, developmental delays, and/or illnesses can be caused by prenatal exposure to drugs, alcohol, or other environmental factors.
Types of Disorders
There are several types of disorders that can be seen during pregnancy:
- Single gene disorders occur when a change in one gene causes a disease. Examples include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, hemophilia, and Marfan syndrome.
- Chromosomal abnormalities occur where there are missing or extra chromosomes, or pieces of chromosomes. Down syndrome, the most common chromosomal abnormality, is caused by an extra chromosome number 21. Chromosome abnormalities can be inherited from a parent or they can happen by chance.
- Multifactorial or complex disorders are caused by a combination of genetic predispositions and environmental factors, which makes it harder to predict who may be at risk. Examples include heart defects, cleft lip or cleft palate, and spina bifida.
- Teratogenic disorders occur when the baby is exposed to substances during pregnancy that cause abnormalities, otherwise known as “teratogens.” Babies are very sensitive in the first trimester, when all of the organs are developing. Teratogens include alcohol, drugs, lead, high levels of radiation exposure, and certain medications, infections and toxic substances.
Testing for Genetic Disorders
There are two types of testing for genetic disorders:
- Screening tests – these tests check the risk of your baby having certain genetic disorders
- Diagnostic tests – these tests can detect if certain genetic disorders are actually present in the baby
Screening and diagnostic tests are optional. They are available to all women, even those who do not have any known risk factors.
Screening tests to check the chance of your baby having certain genetic disorders include:
- Carrier screening is a blood test that tries to determine if either parent carries a genetic change for inherited disorders that could be passed on to the baby. It can also be performed on a saliva sample. The best time to do this screen is before getting pregnant, but it can be done during pregnancy as well. While this screen can check for many conditions at once, it is not currently possible to screen for every disorder that could be inherited.
- Prenatal genetic screens are a series of first and second trimester screens that use blood samples from the mother as well as ultrasounds to check the baby’s risk of having certain common genetic disorders. Examples include Down syndrome and certain birth defects, such as spina bifida.
- Noninvasive Prenatal Testing (NIPT) or cell-free DNA screening is a blood test that checks DNA from the placenta that is found in the mother’s blood. This screens for the most common chromosome abnormalities, such as Down syndrome and trisomy 18, and is most commonly used in high-risk pregnancies.
Diagnostic tests are performed during pregnancy to detect if certain genetic disorders are present in the baby, such as cystic fibrosis or Down syndrome.
Some diagnostic tests can also check for neural tube defects, spina bifida. Diagnostic tests are generally safe procedures when performed by an experienced physician.
However, all procedures carry a small risk of a complication which can include an increased risk of pregnancy loss.
Routine diagnostic tests include:
- Chorionic villus sampling tests a sample of tissue taken from the placenta in the first trimester
- Amniocentesis: Tests a sample of the amniotic fluid taken from the womb in the second trimester
Additional advanced diagnostic tests and technologies available include:
- Fetal blood sampling or percutaneous umbilical blood sampling (PUBS) uses a blood sample from the baby’s umbilical cord to test for genetic disorders. This is usually done when amniocentesis or chorionic villus sampling are not possible.
- Prenatal Chromosome Analysis (Karyotype) is a common genetic test performed on cells obtained from an amniocentesis or CVS that can detect large changes in the chromosomes, such as an extra or missing chromosome or a change in how the chromosomes are put together.
- Prenatal Chromosomal Microarray Analysis (CMA) is a more detailed test performed on cells obtained from an amniocentesis or CVS and tries to detect if any pieces of chromosomes are missing or extra. These extra or missing pieces may be too small to see on a karyotype alone.
- Fetal genomic or whole-exome sequencing (WES) is a diagnostic test for pregnancies with complex fetal conditions that checks almost all of a baby’s genes.
If you are pregnant or planning a pregnancy, you may be referred to a genetic counselor to:
- Assess your personal risk of having a baby with a genetic disorder
- Review your testing options
- Coordinate genetic screenings and diagnostic tests and interpret the results
- Provide emotional support and educational resources for you and your family
- Help you make informed decisions about your pregnancy and your baby’s treatment, and prepare for appropriate medical care
Treatment for Fetal Genetic Disorders
Treatment depends on the genetic disorder and the individual pregnancy. In general, if your baby is diagnosed with a genetic disorder during pregnancy your treatment will include:
- Specialized care from a maternal-fetal medicine physician
- Individualized care the genetic disorder, your pregnancy, and your family’s preferences
- Treatment options ranging from medical therapy during pregnancy, such as fetal interventions, to surgery immediately after birth
- A multidisciplinary, collaborative healthcare team, including genetic counselors, imaging specialists, fetal specialists, fetal and neonatal surgeons as needed, and neonatologists and pediatricians experienced in the treatment of children with genetic disorders
- Support services for you and your family
The Benefits of Specialized Care
Texas Children’s Pavilion for Women offers specialized care for pregnant women whose babies are at risk for or have been diagnosed with genetic disorders, ensuring the best possible care and outcomes.
Our patients benefit from:
- Maternal-fetal medicine specialists experienced in managing these pregnancies and the special needs of mother and baby
- Advanced imaging for early detection and treatment of fetal anomalies
- Expert genetic counseling and testing using the latest technologies at our Prenatal Genetics Clinic, one of the largest of its kind in the country
- Access to Texas Children’s Fetal Center™, a national leader in diagnosing and treating fetal abnormalities
- A full spectrum of fetal therapies with proven fetal outcomes
- Immediate access to Texas Children’s Hospital after birth, including Texas Children’s Newborn Center, home of the level IV neonatal intensive care unit (NICU)
- Support for the emotional challenges of a pregnancy with a genetic disorder or birth defect through The Women’s Place — Center for Reproductive Psychiatry, a unique program dedicated to the care and treatment of women’s reproductive mental health
- Access to expert specialist care, leading edge research, and new treatments for children with known or suspected genetic disorders through the Pediatric Genetics Clinic at Texas Children’s Hospital
- Expert, compassionate pediatric care for children with genetic disorders with the Meyer Center for Developmental Pediatrics at Texas Children’s Hospital
Birth Defects: Causes, Definition & Types
Anti-Fungal Medication and Birth Defects.
A birth defect is something abnormal about your newborn baby’s body. Every four and a half minutes, a baby in the United States is born with a birth defect. A defect, which can affect almost any part of your baby’s body, can be:
- Visibly obvious, a missing arm or a birthmark.
- Internal (inside the body), a kidney that hasn’t formed right or a ventricular septal defect (a hole between the lower chambers of your baby’s heart).
- A chemical imbalance, phenylketonuria (a defect in a chemical reaction that results in developmental delay).
Your baby can be born with one birth defect such as a cleft lip (a gap in their upper lip) or multiple birth defects such as a cleft lip and cleft palate (a hole in the roof of their mouth) together, or even a cleft lip and cleft palate with defects of the brain, heart and kidneys.
Your healthcare provider won’t be able to detect all birth defects right when your baby is born. Some defects, such as scoliosis, might not be apparent until your child is several months old. An abnormal kidney might take years to be discovered.
How common are birth defects?
Birth defects are common. Between 2% and 3% of infants have one or more defects at birth. That number increases to 5% by age one (not all defects are discovered directly after your child’s birth). One every 33 babies born in the United States are affected by birth defects.
What are some other examples of birth defects?
- Duodenal atresia, an obstruction in the small intestine. It can cause polyhydramios (extra fluid around the baby in pregnancy), which can increase the risk of preterm birth. It is sometimes associated with other genetic syndromes.
- Dandy walker malformation, an abnormal development of the posterior fossa (a space in your baby’s skull) and cerebellum (a section of the brain). This birth defect can cause a variety of problems.
- Limb defects, which happen when the fetal amnion (the inner lining of the amniotic sack) wraps around parts of the fetus ( a finger or foot).
Experts don’t know the exact cause of most birth defects, but some reasons are:
- Genetic or hereditary factors.
- Infection during pregnancy.
- Drug exposure during pregnancy.
How do genes and chromosomes affect birth defects?
About 20% of birth defects are caused by genetic or hereditary factors. Genetic causes of birth defects fall into three general categories:
- Chromosomal abnormalities.
- Single-gene defects.
Every human body cell contains 46 chromosomes, and each chromosome contains thousands of genes. Each gene contains a blueprint that controls development or function of a particular body part. People who have either too many or too few chromosomes will therefore receive a scrambled message regarding anatomic development and function.
Down syndrome is an example of a condition caused by too many chromosomes. Because of an accident during cell division, individuals with Down syndrome have an extra copy of a particular chromosome (chromosome 21).
This extra chromosome can cause a typical constellation of birth defects.
Characteristic features of Down syndrome can include developmental delay, muscle weakness, downward slant of the eyes, low-set and malformed ears, an abnormal crease in the palm of the hand and birth defects of the heart and intestines.
With Turner syndrome, a female lacks part or all of one X chromosome. In the affected women, this can cause short stature, learning disabilities and absence of ovaries.
Trisomy 13 (Patau Syndrome) and Trisomy 18 (Edwards Syndrome) are caused by inheriting extra copies of the 13th or 18th chromosome, respectively. These are rarer, more serious conditions which cause severe birth defects that are incompatible with survival after birth.
In addition to inheriting an extra or absent chromosome, deletions or duplications of single genes can also cause developmental disorders and birth defects. One example is cystic fibrosis (a disorder that causes progressive damage of the lungs and pancreas).
Defective genes can also be caused by accidental damage, a condition called “spontaneous mutation.” Most cases of achondroplasia (a condition that causes extreme short stature and malformed bones) are caused by new damage to the controlling gene. In addition, recombination errors can cause translocations of chromosomes which may lead to complex birth defects.
How do environmental factors infection and drugs affect birth defects?
Environmental factors can increase the risk of miscarriage, birth defects, or they might have no effect on your baby at all, depending on at what point during the pregnancy the exposure occurs.
Your developing baby goes through two major stages of development after conception. The first, or embryo stage, occurs during the first 10 weeks after conception. Most of the major body systems and organs form during this time. The second, or fetal stage, is the remainder of the pregnancy.
This fetal period is a time of growth of the organs and of the fetus in general. Your developing baby is most vulnerable to injury during the embryo stage when organs are developing. Indeed, infections and drugs can cause the greatest damage when exposure occurs two to 10 weeks after conception.
Diabetes and obesity can possibly increase your child’s risk of birth defects. Your healthcare provider may suggest that you do your best to manage these conditions before you get pregnant.
Some medicines and recreational drugs can cause birth defects, which are most severe when used during the first three months of pregnancy. Thalidomide, an anti-nausea medicine prescribed during the 1960s, caused birth defects called phocomelia (absence of most of the arm with the hands extending flipper- from the shoulders).
There’s also isotretinoin, previously known as Accutane or Roaccutane. Isotretinoin is a retinoid, a man-made form of vitamin A that’s used to treat skin conditions. It causes fetal retinoid syndrome. Characteristics of fetal retinoid syndrome may include:
- Growth delay.
- Malformations of the skull and face.
- Abnormalities of the central nervous system.
- Abnormalities of the heart.
- Abnormalities of the parathyroid gland.
- Abnormalities of the renal, thymus gland.
Alcohol is the most commonly used drug that causes birth defects. Fetal alcohol syndrome is a term used to describe the typical birth defects caused by the mother’s alcohol use:
- Learning disabilities.
- Developmental delay.
- Poor coordination.
- Abnormalities of facial features.
Another environmental factor that can cause birth defects is uterine constraint. The fetus grows in the mother’s uterus and is surrounded by amniotic fluid (similar to being suspended in a bag of water) that cushions it from excessive pressure.
If the sack of fibers that holds the fluid breaks, bands of fibers from the torn sack can press on the fetus and cause amniotic band syndrome (which can result in partial contraction of or amputation of an arm or leg).
An inadequate amount of amniotic fluid can cause excessive pressure on the entire baby, causing pulmonary hypoplasia (lack of development of the lungs).
Medical science has identified the cause of about 30% of birth defects. That means about 70% remain without a straightforward cause. As many as 50-70% of birth defects are sporadic, and their cause remains unknown. A combination of environmental and genetic factors can increase the risk of certain birth defects.
Healthcare providers can diagnose birth defects before your child’s birth, at birth and after birth. Most are found within your child’s first year.
How are birth defects diagnosed?
During pregnancy you may choose to be screened for birth defects and genetic disorders with ultrasounds or blood tests. If a screening test shows something abnormal, a diagnostic test is often recommended. First trimester screenings check for problems with your baby’s heart, and for chromosomal disorders such as Down syndrome. The screening tests include:
- Maternal blood screen. Blood tests can measure protein levels or circulating free fetal DNA in maternal blood. Abnormal results can indicate increased risk of a fetal chromosomal disorder.
- Ultrasound. An ultrasound looks for extra fluid behind your baby’s neck. That could be a sign of increased risk of a heart defect or chromosomal disorder.
Second trimester screenings check for problems with the structure of your baby’s anatomy. The tests include:
- Maternal serum screen. Blood tests in the second trimester can screen for chromosomal disorders and/or spina bifida.
- Anomaly ultrasound. An anomaly ultrasound checks the size of the baby and checks for birth defects.
More tests may be recommended if a screening test is abnormal. Such diagnostic tests are also offered to women with higher risk pregnancies. The tests include:
- Fetal echocardiogram. This is a focused ultrasound of your baby’s heart, and may be ordered in certain high risk pregnancies, or if a heart defect is suspected on anomaly ultrasound. Not all heart defects can be seen before the birth.
- Fetal MRI. This may be ordered in cases of suspected birth defects, particularly of the baby’s brain or nervous system
- Chorionic villus sampling. Your healthcare provider will collect a very small piece of the placenta for this test. It will be examined for chromosomal or genetic disorders.
- Amniocentesis. Your healthcare provider will collect a small amount of amniotic fluid. Cells are tested for chromosomal disorders and genetic problems cystic fibrosis or Tay-Sachs disease. Amniocentesis can also test for certain infections such as cytomegalovirus (CMV).
Many birth defects may not be diagnosed until after your baby is born. They may be seen immediately, a cleft lip, or diagnosed later. Keep an eye on your baby’s health and report any symptoms to your healthcare provider. Further tests may be needed.
Most birth defects cannot be prevented. There are certain important steps to promote a healthy pregnancy, however. These tips include:
- See your healthcare provider consistently.
- If you are trying to conceive, or if you are sexually active and not using contraception, take a prenatal vitamin with 400 mcg of folic acid.
- Contact your healthcare provider immediately if you think you’re pregnant.
- Don’t drink alcohol.
- Don’t smoke.
- Talk to your healthcare provider about any medications and supplements you’re taking.
- Avoid marijuana and illegal drugs.
The topic of birth defects is a complicated and emotional one. Birth defects are common and can be caused by many different genetic and environmental factors. The fact that the majority of birth defects are without known cause can be frustrating to both parents and healthcare providers.
The topic is emotional in that you may be understandably upset when you learn that your child has a serious birth defect.
You may feel that medical science should be able to prevent, or at least identify in advance, all possible birth defects. You may feel that someone is at fault. You might blame yourself.
You might feel that you either did something that caused the defect or failed to do something that could have prevented it. This is almost never the case.
Sometimes parents feel that the obstetrician is at fault. (An obstetrician is a healthcare provider who specializes in treating women during pregnancy, delivery and recovery.
) The parents might believe that the obstetrician could have ordered a test, prescribed a medicine, or done something differently to prevent the defect.
This is usually not the case, but an honest discussion with the healthcare provider can help address these concerns.
If you are a parent of a child with a birth defect, you should schedule appointments with your child’s healthcare provider at times when you can be present.
You and the healthcare provider should thoroughly discuss possible causes, testing, treatment and referrals to specialists and support groups.
You should continue these discussions and should continue asking questions until you are completely satisfied.
A note from Cleveland Clinic
The very last thing an expectant parent wants to hear is that there is something wrong with their unborn child or with their infant. Most birth defects can’t be prevented, but you can take some steps to reduce the lihood of environmental effects. Remember to always discuss your concerns with your healthcare provider and follow their instructions regarding screening tests, medications, etc.