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Fears that the baby will be born with a defect or handicap can overwhelm some parents during the long nine months until birth. Today, some of those fears can be silenced through an array of tests to learn if the baby's chromosomes are normal. Although some questions remain until the delivery, many can be answered before then.
The prenatal tests to detect some birth defects are easier to understand if you know about chromosomes and genes. Every individual has 468 chromosomes. These are the markers that carry the basic characteristics that make us human beings. A baby has 234 chromosomes from each parent.
On the chromosomes are many genes that carry your unique features such as hair colour, left or right-handedness or risk of some diseases. A trait in your family can be passed from one generation to the next on a gene. When prenatal testing is done, in many cases it is to detect an abnormal gene that has been passed on.
During the first prenatal visit, you will be asked many questions about your health, the baby's father's health, and the medical history of the two families. The reason for so many questions is that there are many genetic diseases within families. One in 20 newborns has a genetic defect that is detectable at birth.
Before you see your doctor for your first prenatal visit, try to learn about the medical history of the families of both parents. This will help the doctor plan your care and give you a chance to ask questions about how you might be affected.
Before you see your doctor you should have answers to these questions:
Even though many pregnant women will not answer yes to these questions, the fear of a genetic disease is still real. Who then should be screened further for genetic diseases?
Pregnant women of all ages should be offered maternal serum screening to test for certain components in the blood. A blood sample is taken from the mother, preferably when the pregnancy is between 15 and 16 weeks. The results are evaluated in relation to the mother's age, race, weight and whether there is one or more babies. From this test, it is possible to determine the degree of risk that there is Down's syndrome or another genetic disorder called Trisomy 18. It is also possible to determine if the baby may have a neural tube defect. (This is either an opening of the spinal cord or a baby without a brain.)
Future parents are often anxious about the results but 19 of every 20 women having a maternal serum screening will be told that no further testing is indicated. If a report comes back as abnormal, remember it is just a screening test. Further testing, such as ultrasound and amniocentesis will usually be required. Amniocentesis samples the fluid around the baby. Most of the time when the screening results are abnormal, further tests show a normal baby.
Ultrasound is a screening test offered when a woman is about 18 weeks pregnant. This test involves passing sound waves through the abdomen of the mother. There is no risk to mother or baby and the test causes no discomfort. The image that results helps to identify the development of the baby. Eighteen weeks is the best time for the radiologist to view the major organs of the baby. These include the brain, the face, the heart, the stomach, the kidneys, the bowels, the bladder, the spine and the bones.
If there are concerns with the findings on the ultrasound a repeat scan may be done in two weeks or amniocentesis may be recommended. Sometimes, ultrasound detects some abnormality that turns out to be of no concern, but it is a worrisome time as parents wait to learn more about the finding.
Amniocentesis is a test that involves removing about 30 millilitres or two tablespoons of amniotic fluid (the fluid that surrounds the baby). This amniotic fluid is used to assess the baby's chromosomes. An ultrasound is used to help guide the doctor doing the test.
Most times amniocentesis is offered to pregnant mothers who will be 35 years or older when the baby is born. It is also offered to pregnant mothers who have had a screening test that suggests a chromosomal disorder. Amniocentesis will be offered when a previous pregnancy has resulted in a child with a chromosome abnormality or a parent has a known chromosome abnormality.
Amniocentesis is usually done at about 15 weeks of the pregnancy. It can take a few days to a few weeks to get the results back, depending on the type of testing done to determine the baby's chromosomes. The fluid can also be checked for alpha-fetoprotein levels that help determine if the baby has a neural tube defect.
If you have an amniocentesis you may have some vaginal spotting or amniotic fluid leakage, but this usually resolves within two to three days. Within one week the baby will replace the amniotic fluid that is removed. There is a one in 200 chance amniocentesis will cause a miscarriage to occur.
CVS involves taking a small sample of tissue from the edge of the placenta. To do this, a small catheter is inserted either through the cervix or through the abdomen. Again, this test is done with ultrasound guidance to help locate the placenta within the womb.
With this test, there is the risk of infection, spotting, loss of amniotic fluid and miscarriage. There is also a possibility that the mother's cells will be collected with the baby's cells, giving false information about the pregnancy. Another concern is the possible increase in limb abnormalities in the baby when CVS is performed.
For these reasons, it is a procedure that has not been used as widely as amniocentesis. CVS is performed when the pregnant woman is between nine and 12 weeks pregnant. This is a time advantage over amniocentesis and gives parents earlier answers about the genetic health of their baby.
The world of genetics and obstetrics is advancing rapidly. Today fetal blood cells can be obtained directly from the baby by sampling blood from the umbilical cord. For some genetic disorders it is possible to obtain tissue directly from the baby for analysis.
Another test being investigated is identification of fetal cells that occur within the mother's blood circulation. Separation of these fetal cells from the mother's cells will allow for an inexpensive and less invasive method of determining a baby's genetics.
For those using infertility treatments such as in vitro fertilization (IVF), testing is being done on early embryos to learn genetic make-up. This will allow only healthy embryos to be implanted into the uterus after fertilization has occurred.
The field of prenatal genetic testing is ever changing. Write your questions down and take them with you to talk to your doctor or midwife. Together you will be able to make the best decisions about appropriate tests for you in pregnancy.
It used to be said that it could be an advantage to be able to choose your parents, particularly if you have a genetic disorder. Although we cannot choose our parents, we are reaching a point where parents can choose the genes of their children. There are many complex and difficult personal, ethical and moral questions raised by these issues. Will children in the next generation wear T-shirts with the slogan "My genes are screened?"
FAMILY HEALTH is written with the assistance of |
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