Chorionic Villus Sampling
Indications for CVS (Genetics & Inherited Conditions)
Many indications exist for performing CVS, including advanced maternal age, abnormal results from prenatal screening tests, and known or suspected family history of genetic abnormalities. Advanced maternal age, generally considered to be greater than thirty-give years, is one of the most important indications for CVS because a woman’s eggs age along with her, which can increase the chance for errors during cell division. The most common error is called nondisjunction and occurs in anaphase during meiosis. Nondisjunction is the failure of two sister chromosomes to separate in one parent and thus the inheritance of two copies of that particular chromosome from that parent and one copy from the other parent, resulting in three copies of a chromosome instead of the usual two. This resulting trisomy is generally sporadic in nature and can be detected through CVS.
Prenatal screening tests involve quantifying maternal levels of certain pregnancy-related hormones, including AFP, PAPP-A, hCG, E3, and inhibin A, and performing an ultrasound to evaluate the fetus for nuchal translucency. Combining the results of these tests, a risk of fetal abnormality can be calculated, and CVS may then be indicated for further evaluation of the fetus. The prenatal screening tests can predict only the likelihood of genetic disorders, while CVS is able to provide an actual diagnosis. In cases where the parents are known carriers of a genetic...
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Diagnostic Capabilities and Limitations (Genetics & Inherited Conditions)
Chorionic villus sampling can detect a variety of genetic syndromes. Chromosomal disorders including trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome), Turner syndrome, and Klinefelter syndrome can be diagnosed. Numerous other genetic diseases such as cystic fibrosis, Tay-Sachs disease, congenital adrenal hyperplasia (CAH), and sickle-cell disease are also diagnosed through CVS. Neural tube defects such as spina bifida and anencephaly cannot be diagnosed with CVS testing and require amniocentesis if suspected.
Confusion may occur when placental mosaicism is present. This occurs when the cells of the placenta sampled through CVS indicate an abnormality while others are unaffected, leading to potentially false positive results. Placental mosaicism is rare, occurring in only about 1-2 percent of pregnancies. In this special case, amniocentesis will be performed to confirm the suspected mosaicism. It is also possible to have a negative CVS result and still have a baby with a genetic disorder. The rate of false positive or false negative results can vary widely with each genetic disorder.
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Laboratory Process (Genetics & Inherited Conditions)
Chorionic villus sampling is performed either transabdominally or transcervically to sample cells of the chorionic villus of the placenta; the cells are analyzed in a laboratory. The cells are subsequently halted in the middle of cell division and examined microscopically for karyotype abnormalities such as too many or too few chromosomes and abnormal variations in size of the chromosomes.
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Early Intervention (Genetics & Inherited Conditions)
At this point in time, the scope of genetic disorders able to be diagnosed through chorionic villus sampling for which in utero treatment is available is small. One such disorder is congenital adrenal hyperplasia, a genetic disorder caused by lack of an enzyme that leads to a hormonal deficiency and possibly ambiguous genitalia. If the fetus is treated with these vital hormones within a narrow, critical period of time, then the need for postnatal intervention can be avoided along with the gender assignment confusion that often results for parents. Currently, for most other genetic disorders diagnosed through CVS, the primary intervention available is termination of the pregnancy, which can pose a considerable emotional dilemma for the parents.
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Impact (Genetics & Inherited Conditions)
Chorionic villus sampling allows for earlier diagnosis of a wide array of genetic disorders than does amniocentesis. It is performed in the first trimester, between ten and twelve weeks of gestation, whereas amniocentesis is generally performed in the second trimester, between fifteen and seventeen weeks of gestation. If termination of the pregnancy is indicated, it can then be performed in the first trimester, potentially allowing for a safer, less physically traumatic procedure. It is also likely to be less psychologically damaging to the parents to have termination performed at an earlier time.
CVS is currently widely available, and increasing numbers of women are undergoing the procedure. The Centers for Disease Control and Prevention (CDC) reported a large increase in the amount of CVS procedures performed in the late 1980’s and early 1990’s, especially among women greater than thirty-five years of age. This increase in procedure rate has resulted in a large percentage of the pregnant female population becoming aware of their child’s genetic condition prior to birth and allows more time to prepare for the care of the neonate. The future impact of CVS is likely to be wide as prenatal interventions for commonly diagnosed genetic conditions are discovered and the survival rate of the affected offspring is greatly increased.
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Further Reading (Genetics & Inherited Conditions)
Creasy, Robert K., Robert Resnick, and J. D. Iams. Creasy and Resnick’s Maternal-Fetal Medicine: Principles and Practice. 6th ed. Philadelphia: Saunders/Elsevier, 2009. A popular reference text for genetic disorders from a maternal-fetal medicine viewpoint.
Harms, Roger W., ed. Mayo Clinic Guide to a Healthy Pregnancy. New York: HarperCollins, 2004. A resource for non-medical professionals regarding pregnancy and prenatal testing options.
Miller, Orlando J., and Eeva Therman. Human Chromosomes. 4th ed. New York: Springer, 2001. An understandable, concise introduction to chromosomes for all readers.
Pierce, Benjamin. Genetics: A Conceptual Approach. 3d ed. New York: Macmillan, 2007. An excellent, comprehensive approach to the field of genetics.
Queenan, John T., John C. Hobbins, and Catherine Y. Spong. Protocols for High-Risk Pregnancies. 4th ed. Hoboken, N.J.: Wiley-Blackwell, 2005. A comprehensive description of chorionic villus sampling.
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Web Sites of Interest (Genetics & Inherited Conditions)
March of Dimes: Chorionic Villus Sampling (CVS). http://www.marchofdimes.com/pnhec/159_521.asp
Mayo Clinic: Chorionic Villus Sampling. http://www.mayoclinic.com/health/chorionic-villus-sampling/MY00154
National Library of Medicine and the National Institutes of Health. MedlinePlus. http://www.nlm.nih.gov/medlineplus/ency/article/003345.htm
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Chorionic Villus Sampling
Indications and Procedures (Magill’s Medical Guide, Sixth Edition)
Chorionic villus sampling can be performed between the tenth and twelfth weeks of pregnancy to detect genetic and chromosomal abnormalities. The procedure is recommended when there is increased risk of genetic disorders in the fetus such as Down syndrome, sickle cell disease, and muscular dystrophy.
Chorionic villus sampling involves collecting a small sample of the chorionic villi, the fingerlike projections on the developing placenta, which delivers food and oxygen to the fetus. A sample of chorionic villi can be obtained either by inserting a needle through the abdomen or by entering the cervix with a small flexible catheter through the vagina. The choice of approach depends on the position of the placenta. Ultrasound is used to locate the fetus and the placenta and its villi.
A 10- to 25-milligram sample is collected using a syringe, which is then purified and sometimes cultured. Since the chorionic villi originate from the same cell as the fetus, they normally have the same genetics. Results are available within days.
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Uses and Complications (Magill’s Medical Guide, Sixth Edition)
Along with exposing genetic and chromosomal disorders, chorionic villus sampling can be used to determine the sex of the embryo but should never be used for this purpose alone because of the risks involved. Testing can be done early in the pregnancy. Therefore, if the woman should choose to terminate her pregnancy, an easier first-trimester abortion can be performed. If the results from the test are favorable, the parents have an early peace of mind.
Possible complications from chorionic villus sampling include vaginal bleeding and cramping. More serious risks involve spontaneous abortion and even possible fetal injury. The rate of miscarriage is about 1 percent higher with chorionic villus sampling than with amniocentesis, performed after sixteen weeks and yielding the same information.
Some studies suggest that chorionic villus sampling itself may cause some birth defects; others do not. Also, the procedure can be inaccurate. Abnormalities may occur in some placental cells but not in the fetus. This might lead to aborting a healthy fetus. With the guidance of a physician, the risks and benefits should be compared with other available procedures.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Caughey, Aaron B., Linda M. Hopkins, and Mary E. Norton. “Chorionic Villus Sampling Compared with Amniocentesis and the Difference in the Rate of Pregnancy Loss.” Obstetrics and Gynecology 108, no. 3 (September, 2006): 612-616.
Ettorre, Elizabeth, ed. Before Birth: Understanding Prenatal Screening. Brookfield, Vt.: Ashgate, 2001.
Filkins, Karen, and Joseph F. Russo, eds. Human Prenatal Diagnosis. 2d rev. ed. New York: Marcel Dekker, 1990.
Harper, Peter S. Practical Genetic Counselling. 6th ed. New York: Oxford University Press, 2004.
Lichtman, Ronnie, Lynn Louise Simpson, and Allan Rosenfield. Dr. Guttmacher’s Pregnancy, Birth, and Family Planning. Rev. ed. New York: New American Library, 2003.
Moore, Keith L., and T. V. N. Persaud. The Developing Human. 8th ed. Philadelphia: Saunders/Elsevier, 2008.
Pierce, Benjamin A. The Family Genetic Sourcebook. New York: John Wiley & Sons, 1990.
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Chorionic Villus Sampling (Encyclopedia of Medicine)
Chorionic villus sampling (CVS), also known as chorionic villus biopsy, is a prenatal test that can detect genetic and chromosomal abnormalities of an unborn baby.
Chorionic villus sampling is performed on pregnant women who are at risk for carrying a fetus with a genetic or chromosomal defect. Although it carries a slightly higher risk, CVS may be used in place of amniocentesis for women who have one or more of the following risk factors:
- Women age 35 and older. The chance of having a child with Down syndrome increases with maternal age. For instance, the chance of having a baby with Down syndrome is one in 378 for a 35-year-old woman and increases to one in 30 for a 45-year-old woman.
- A history of miscarriages or children born with birth defects.
- A family history of genetic disease. Prenatal genetic testing is recommended if either the mother or father of the unborn baby has a family history of genetic disease or is known to be a carrier of a genetic disease.
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Chorionic Villus Sampling (Encyclopedia of Nursing & Allied Health)
Chorionic villus sampling (CVS) is a prenatal procedure for the removal by needle of chorionic villi and culture and examination of the fetal cells obtained. The cells are used in tests for genetic and chromosomal abnormalities of a fetus as early as 10 to 12 weeks of gestation.
Women who are at risk of carrying a fetus with a genetic or chromosomal defect may be counseled to have a prenatal screening test such as CVS or amniocentesis. CVS, which is performed at 10 to 12 weeks after a woman's last menstrual period, may be offered as an alternative to amniocentesis, the more commonly used test for prenatal diagnosis of genetic disorders, which is performed usually at 15 to 18 weeks. Earlier diagnosis of congenital defects is especially beneficial in cases where the parents' desire to know the results as early in preg- nancy as possible, for instance, when therapeutic abortion is being considered, as the risks associated with abortion increase with gestational age.
Prenatal screening can diagnose some genetic and virtually all chromosomal disorders and is advised for women who have one or more of the following risk factors:
- Women age 35 and older. The chance of having a child with certain chromosomal birth defects increases with maternal age. The most common chromosomal disorder is Down syndrome, a combination of mental and physical abnormalities caused by the presence of an extra copy of chromosome 21. The occurrence of Down syndrome in children born to women in their 20s is approximately 1 in 1,250, but increases to 1 in 400 by age 35, and to 1 in 100 at age 40.
- A child or previous pregnancy with a birth defect, or a history of miscarriages. A woman who has already had a child or pregnancy diagnosed with a genetic birth defect or chromosomal abnormality, or who has had multiple miscarriages, is at increased risk of having a child with a genetic disorder.
- Determination of the sex of a fetus when the mother is known to be a carrier of a sex-linked genetic disease (for example, hemophilia A).
- Other family history of genetic disease. Couples who do not have an affected child but who have family medical histories of genetic or chromosomal abnormalities or are known through genetic screening to be carriers of an inherited disease are at increased risk of having an affected child. Prenatal testing is offered only when the suspected condition can be diagnosed before birth.
Chorionic villus sampling usually is not recommended for:
- A woman whose pregnancy has progressed further than about 12 weeks, counted from the first day of the last menstrual period.
- A woman who is experiencing bleeding or spotting.
- In the presence of certain vaginal infections.
- When there are uterine abnormalities, such as a bicornuate (double) uterus or uterine fibroids.
- Women who would not consider intervening in a preg- nancy where a genetic abnormality is detected.
Women who are concerned about the risk of miscarriage associated with CVS can be offered amniocentesis or a noninvasive alternative. One such alternative is a maternal blood test called triple marker screening or multiple marker screening, which is performed no sooner than 15 weeks but no later than 20 weeks of pregnancy. A sample of the pregnant woman's blood is analyzed for three substances produced by the fetus and passed into the mother's blood: alpha fetoprotein (AFP), human chorionic gonadotropin (HCG), and unconjugated estriol (UE3). Elevated AFP may indicate the presence of anencephaly or spina bifida; HCG is increased and AFP and UE3 are decreased in Down syndrome. This screening test, however, does not definitively diagnose a genetic defect and has a relatively high rate of false negatives, but it can help to identify an unborn baby at increased risk for these birth defects. A pregnant woman whose triple marker results are indicative of a fetus at risk would be encouraged to undergo further screening, such as ultrasound and/or amniocentesis (the timing of the triple marker screening rules out CVS) to provide a definitive diagnosis.
Since only cells and not fluid are collected, CVS does not allow evaluation of AFP to indicate the presence of neural tube defects. AFP is then generally measured by a maternal blood test at 150 weeks, but with less accuracy than would be obtained with an amniotic fluid sample.
A CVS sample may be obtained either via the vagina and cervix (transcervical CVS) or through the abdomen (transabdominal CVS). Woman who have a retroverted (tipped) uterus should be sampled transabdominally, since studies have shown the risk of miscarriage to be lower than when the procedure is done transcervically. In cases where the location of the placenta contraindicates transabdominal CVS, amniocentesis should be offered as an alternative screening test. Amniocentesis, however, is only rarely performed in the first trimester.
Although CVS is over 99% accurate in ruling out certain chromosomal birth defects and specific genetic problems, it is slightly more likely than amniocentesis to give inconclusive results. Amniocentesis, then, may be used as a back-up screening procedure. However, the patient should be cautioned that not all birth defects can be ruled out before birth and no prenatal test can guarantee the birth of a healthy baby. Because it is performed earlier in pregnancy than amniocentesis, CVS sampling is more likely to detect fatal genetic diseases that result in miscarriages after the diagnosis has been established.
Chorionic villus sampling has been in use increasingly since the 1980s. The CVS procedure involves taking a sample of the chorion frondosumhe part of the chorionic membrane that contains the villi, microscopic, finger-like projections that emerge from the chorionic membrane to form the placentaor laboratory analysis. The chorion is the outermost membrane surrounding the developing fetus; the amnion is the inner membrane that contains the amniotic fluid. The cells that make up the chorionic villi are of fetal origin, and, thus, normally have the same genetic makeup as the fetus. The sample may be obtained with a catheter, a thin, plastic tube, inserted through the vagina and the cervix (transcervical CVS) or with a needle through the abdominal wall (transabdominal CVS); both sampling methods take about five minutes to perform (not including preparation time), are equally effective, and carry similar risks.
Chorionic villus sampling is best performed between 10 and 12 weeks of pregnancy. Abdominal ultrasound is used to determine the position of the uterus, the position of the placenta within the uterus, and the size of the amniotic sack. The woman assumes the lithotomy position (on her back with her feet in stirrups). In transcervical CVS, the vulva, vagina, and cervix are thoroughly cleansed with antiseptic; no anesthetic is required. A speculum is inserted into the vagina and opened, then, using ultrasound as a guide, the doctor inserts a catheter through the cervix and into the uterus. The catheter is carefully advanced to the chorionic villi and suction is applied with the syringe attached to the catheter to obtain a small sample of the villi. The catheter is then carefully withdrawn.
In transabdominal CVS, the appropriate area on the woman's abdomen is cleansed thoroughly with antiseptic and a local anesthetic may be injected to numb the area. With ultrasound guidance to strictly avoid the placenta, a long needle is inserted through the woman's abdominal wall, through the uterine wall and to the chorionic villi. Suction is applied with the syringe attached to the needle to obtain a small sample of the villi, and the needle is then carefully withdrawn.
Most women report that transcervical CVS feels similar to the procedure for a Pap smear. The passage of the catheter through the cervix may cause cramping, and some women experience cramping or pinching sensations when the sample is taken. There is generally little or no discom- fort associated with the transabdominal procedure. Occasionally, when insufficient villus material is obtained, a second sampling procedure must be performed.
The chorionic villus sample is immediately placed into a sample dish containing nutrient medium for transport to the cytogenetics laboratory. At the laboratory, the sample is examined under the microscope so that any contaminating cells or material may be carefully removed. The villi can be analyzed immediately, or incubated for a day or more to give the cells time to undergo division. When the cells are in the midst of dividing, they are spread onto a slide and examined under a micro- scope. Cells that have clearly separated chromosomes are photographed to allow analysis of the type and number of chromosomes. The chromosomal images are collected in a report called a karyotype, which shows the number, shape, size, and arrangement of chromosomal pairs. For biochemical studies, deoxyribonucleic acid (DNA) is extracted from cultured chorionic villus cells. Depending upon which tests are performed, results may be available as early as two days or up to ten days after the procedure.
The chorionic villus sampling procedure costs about $3,000, including ultrasound, laboratory, and counseling charges. Some insurance plans may provide some level of coverage for this test.
Thorough pre-CVS counseling is strongly recommended to give the couple the opportunity to make informed decisions about prenatal diagnosis. The couple should be provided with literature about CVS and genetic screening options to read prior to the counseling conference, so that any questions or concerns they may have can be addressed at that time. Prior to the procedure, the woman will likely be asked to sign a consent form.
For the procedure itself, the woman will be instructed to drink fluids and refrain from urinating so that the bladder is partly filled; excessive and uncomfortable bladder filling is not necessary. A filled bladder can help to properly position the uterus and create a better ultra- sound picture for guiding the CVS procedure.
After the sample is taken, the fetal heartbeat is checked by ultrasound before the woman leaves the examination room. A follow-up ultrasound procedure may be scheduled two to four days after CVS to ascertain the health of the fetus.
Most physicians recommend that the woman have someone drive her home after the CVS procedure and that she limit strenuous activity for the remainder of the day. A women who experiences excessive bleeding, vaginal discharge, fever, or abdominal pain after the procedure should consult her doctor.
Women with Rh negative blood may receive a Rho(D) immune globulin (RhoGAM) injection to avoid Rh incompatibility.
Advances in prenatal treatment have made it possible to treat some genetic defects diagnosed by prenatal screening before birth. Congenital adrenal hyperplasia (CAH), for example, is an inherited birth defect in which an enzyme deficiency causes a female fetus to develop abnormal external genitalia by the 16th week of pregnancy. Prenatal diagnosis by CVS in pregnancies known to be at risk of CAH allows the fetus to be treated with hormones during the critical period of development from 10 to 16 weeks of gestation and can circumvent the need for surgery after birth. For conditions in which prenatal treatment is not available, prenatal diagnosis can allow parents the opportunity to discuss their options with genetic counselors or other health care providers, to plan the delivery, and to prepare emotionally for the birth.
Of women who undergo transcervical CVS, one third experience minimal vaginal spotting and 70% experience vaginal bleeding; bleeding that is heavier than during a normal menstrual period should be reported to the doctor. One out of five women experience cramping following the procedure. Rupture of the amniotic membranes is a rare but serious complication that can lead to infection and/or miscarriage. The risk of miscarriage after CVS is 1%, compared to 0.5% for amniocentesis. A woman with Rh negative blood who is carrying an Rh positive fetus may be at an increased risk for developing Rh incompatibility following CVS and should be treated with Rho immune globulin.
In the early 1990s, there were several reports linking babies born with missing or shortened fingers or toes and abnormalities of the tongue and lower jaw with CVS performed before the tenth week of pregnancy. These reports raised concerns about the safety of CVS, although this type of limb defect is known to occur in approximately 1 out of every 1,700 babies. Subsequent studies of the risk of limb defects following CVS have produced conflicting results, and CVS safety studies continue. A study by the World Health Organization's CVS Registry, which performs ongoing assessment of CVS, reported in 1999 that the risk of these limb defects in babies born to more than 200,000 women who had CVS was not significantly increased compared to the norm. CVS is now generally performed only at ten weeks or later, and all women being offered CVS should be advised of the limited risk of limb defects.
There is risk with CVS of getting a "placental mosaicism" artifact in which the cultured cells contain some abnormal chromosomes that originate in the placenta and are not related to the fetus. Mosaicism occurs when cells have two or more distinct chromosome counts. This occurs when nondisjunction (failure of chromatids to separate) occurs in germ line cells (after fertilization). The fetus may be normal, and the only way to rule out actual mosaicism is to follow up with amniocentesis. There is also a risk that insufficient chorionic villi are collected for analysis, or that the cells collected are contaminated with cells of maternal origin. In this case, a second sampling procedure is performed about a week later, or amniocentesis may be offered as an alternative.
The chorionic villus cells are cultured and photographed through a microscope during cell division to obtain images of the chromosomes. The images are sorted, identified, and reported in a karyotype. Humans have 23 pairs of chromosomes, including the sex chromosomes. The karyotype allows detection of aneuploidies (extra copies of chromosomes), chromosomal deletions, and gross chromosomal translocations. The gender of the fetus is identified from the sex chromosomes, and can be reported to the parents upon request.
DNA studies are performed when indicated by a family history of genetic disorders. DNA is the biochemical molecule that stores genetic information in the chromosomes. The DNA is extracted from the chorionic villus cells, and analysis of the DNA allows prenatal diagnosis of over 200 diseases, including Tay-Sachs disease, cystic fibrosis, sickle-cell anemia, and muscular dystrophy.
Health care team roles
The genetic counselor, physician, or other health care provider will provide information to the couple considering CVS and explain the procedure and its risks, and alternative procedures. Counselors can also advise parents of their options when they learn that their unborn child has an inherited disorder and/or help them prepare emotionally for the delivery of a child with a birth defect.
The obstetrics team carries out the ultrasound and CVS procedure, and ensures that the chorionic villus cells are properly handled for transport to a cytogenetics laboratory. The team of physician(s) and nurses also provide practical and psychological support for the couple undergoing prenatal diagnosis.
Technologists in the cytogenetics laboratory perform cell culture on the chorionic villus cells, fix a sample of cells during cell division, prepare the cells on a slide for microscopic analysis, and make photographs of the chromosomes of dividing cells to be collated in a karyotype. Cytogenetic technologists are also involved in the extraction of DNA from the cells and the biochemical testing of the DNA.
The obstetrician receives special training in the procedure for collecting the chorionic villus specimen. Cytogenetic laboratory technologists, CLSp(CG) are specially trained in sterile techniques for cell culture,
Alpha fetoprotein serum protein produced by the fetus during pregnancy and passed to the moth- er's blood, useful in the prenatal diagnosis of multiple births or birth defects.
Amniocentesis prenatal screening procedure in which a sample of amniotic fluid from the amniotic sac in the uterus of a pregnant woman is obtained by inserting a needle through the abdominal wall.
Aneuploidyn irregular number of chromosomes caused by the loss or addition of one or more chromosomes or parts of chromosomes.
Chromosomesightly compressed rod-like structures that carry DNA; humans have 23 pairs of chromosomes including the sex chromosomes.
Cystic fibrosisn inherited chronic disease of the exocrine glands, characterized by the production of viscous mucus that obstructs the pancreatic ducts and bronchi, leading to infection and fibrosis.
Down syndromelso called trisomy 21, a genetic disorder, associated with the presence of an extra copy or a rearrangement of chromosome 21, characterized by mild to severe mental retardation, weak muscle tone, a low nasal bridge, and epicanthic folds at the eyelids; formerly called mongolism.
Human chorionic gonadotropin hormone produced by the developing placenta that stimulates the production of estrogen and progesterone; its presence in maternal blood or urine is used to diagnose pregnancy.
Karyotype report in which photographic images of the chromosomes of a cell are displayed as a systematized arrangement of pairs in descending order of size. photomicrography, construction of the karyotype report, and biochemical analysis of DNA.
Muscular dystrophyn inherited disease in which muscles become gradually wasted and are replaced by scar tissue and fat, sometimes also affecting the heart.
Neural tube defectny of a group of inherited abnormalities of brain and spinal cord development, including spina bifida and anencephaly, caused by failure of the neural tube to close prop- erly during development.
Rh incompatablilityn Rh negative person who is exposed to Rh positive red blood cells. When an Rh negative mother becomes pregnant with an Rh positive fetus, the fetal red blood cells may enter the maternal circulation and stimulate production of Rh antibodies. This process can be prevented by administration of Rho immune globulin prior to or during the pregnancy.
Sickle-cell anemian inherited chronic blood disease that occurs primarily among persons of African descent characterized by abnormal hemoglobin that causes red blood cells to become sickle-shaped and nonfunctional, leading to an enlarged spleen, chronic anemia, weakness, joint pain, and formation of blood clots.
Tay-Sachs disease rare and fatal inherited dis- ease occurring chiefly in persons of eastern European Jewish origin, characterized by a red spot on the retina, gradual blindness, and paralysis.
Ultrasoundlso called ultrasonography, a diagnostic imaging technique that uses reflected high- frequency sound waves to visualize internal body structures or organs, especially useful as a non- invasive prenatal diagnostic tool.
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Patricia L. Bounds, Ph.D.