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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, like 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 based on 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