Which mother is at greatest risk of having a child with a chromosomal abnormality
Chromosomes are stick-shaped structures in the middle of each cell in the body. Each cell has 46 chromosomes grouped in 23 pairs. When a chromosome is abnormal, it can cause health problems in the body. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or more of these: Show
Errors during dividing of sex cells (meiosis)Meiosis (my-OH-sis) is the process in which sex cells divide and create new sex cells with half the number of chromosomes. Sperm and eggs are sex cells. Meiosis is the start of the process of how a baby grows. Normally, meiosis causes each parent to give 23 chromosomes to a pregnancy. When a sperm fertilizes an egg, the union leads to a baby with 46 chromosomes. But if meiosis doesn’t happen normally, a baby may have an extra chromosome (trisomy), or have a missing chromosome (monosomy). These problems can cause pregnancy loss. Or they can cause health problems in a child. A woman age 35 years or older is at higher risk of having a baby with a chromosomal abnormality. This is because errors in meiosis may be more likely to happen as a result of the aging process. Women are born with all of their eggs already in their ovaries. The eggs begin to mature during puberty. If a woman is 35 years old, the eggs in the ovaries are also 35 years old. You may be referred for genetic counseling or testing if you’re age 35 or older when you are pregnant. Men make new sperm ongoing. So age doesn’t increase the risk for chromosome abnormalities for older fathers a lot. But newer studies suggest that rare abnormalities do occur. Errors during dividing of other cells (mitosis)Mitosis (my-TOH-sis) is the dividing of all other cells in the body. It’s how a baby in the womb grows. Mitosis causes the number of chromosomes to double to 92, and then split in half back to 46. This process repeats constantly in the cells as the baby grows. Mitosis continues throughout your lifetime. It replaces skin cells, blood cells, and other types of cells that are damaged or naturally die. During pregnancy, an error in mitosis can occur. If the chromosomes don’t split into equal halves, the new cells can have an extra chromosome (47 total) or have a missing chromosome (45 total). Substances that cause birth defects (teratogens)A teratogen (ter-AT-uh-jen) is something that can cause or raise the risk for a birth defect in a baby. They are things that a mother may be exposed to during her pregnancy. Teratogens include:
Researchers have 2 ways of finding out if a substance is a teratogen:
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 DisordersFactors that increase your risk of having a baby with a genetic disorder include:
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 DisordersThere are several types of disorders that can be seen during pregnancy:
Testing for Genetic DisordersThere are two types of testing for genetic disorders:
Screening and diagnostic tests are optional. They are available to all women, even those who do not have any known risk factors. Screening TestsScreening tests to check the chance of your baby having certain genetic disorders include:
Diagnostic TestsDiagnostic 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:
Additional advanced diagnostic tests and technologies available include:
Genetic CounselingIf you are pregnant or planning a pregnancy, you may be referred to a genetic counselor to:
Treatment for Fetal Genetic DisordersTreatment 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:
The Benefits of Specialized CareTexas 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:
Which woman is at the greatest risk of bearing a baby with Down syndrome?Women over age 35 are at higher risk for giving birth to a child with Down syndrome. People have long recognized there is a connection between maternal age and Down syndrome.
What is the risk of chromosomal abnormalities?While most babies are born healthy, approximately 3-5% will be affected with certain birth defects or genetic conditions. In all pregnancies, tests are offered that can tell if the pregnancy may be at high risk for a condition called a chromosome abnormality. Decisions about testing in pregnancy are personal.
Why advanced maternal age has increased likelihood of having a child with chromosomal abnormalities?Fetal chromosomal abnormalities may be caused by a nondisjunction phenomenon that occurs in the period of meiosis during maternal oogenesis, which has been reported to have a direct association with maternal age. Therefore, pregnancy in advanced age is a critical risk factor for fetal chromosomal abnormalities [2-4].
What causes chromosomal abnormalities in fetus?Some genetic disorders are caused by chromosomal abnormalities due to errors in meiosis, the process which produces reproductive cells such as sperm and eggs. Examples include Down syndrome (extra chromosome 21), Turner Syndrome (45X0) and Klinefelter's syndrome (a male with 2 X chromosomes).
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