Douglas Bevis’s description of amniocentesis, the removal of amniotic fluid from pregnant women, led to the procedure becoming a standard diagnostic tool to check fetal maturity, health, and genetic abnormalities. Amniocentesis is used especially with pregnant women over the age of thirty-five.
At the beginning of a human pregnancy—conception—an egg and a sperm unite to produce the fertilized egg that will become a new human being. After conception, the fertilized egg passes from the oviduct into the uterus, while dividing and becoming an organized cluster of cells capable of carrying out different tasks in the nine-month-long group of events that most often leads to a newborn baby.
About a week after conception, the cluster of cells, now a vesicle containing the future human embryo, attaches to the uterine lining, penetrates it, and becomes intimately intertwined with uterine tissues. In time, the merger between the vesicle and the uterus results in formation of a placenta that connects the mother and the baby-to-be, the embryo, and an amniotic sac filled with the amniotic fluid in which the embryo floats.
Diabetic women and women over thirty-five years of age have higher than usual chances of delivering babies who have birth abnormalities. Many other factors inferred from the medical history an expecting woman provides to her physician can indicate the possible appearance of birth abnormalities. In some cases, these birth abnormalities may be so serious that the termination of the pregnancy may need to be considered. Disorders that produce extreme mental damage or fatal genetic disease can cause great havoc in affected families. In cases such as these, tragedy can be averted sometimes via therapeutic abortion where the data clearly support it.
In other cases, knowledge of possible physical problems in a fetus may allow their treatment—in the uterus—and save the newborn from problems that could persist throughout life or lead to death in early childhood. Information is obtained through the examination of the amniotic fluid in which the fetus is suspended throughout pregnancy. The process for obtaining this fluid is called amniocentesis. Amniocentesis, then, is a technique that may be used to allow physicians to examine the health and the presence or absence of genetic abnormalities in human fetuses before they are born. Whenever a genetic defect is suspected, amniocentesis is performed. Usually, sixteen-week-old fetuses are used because it is a generally safe time to carry out the procedure, samples of amniotic fluid large enough for detailed analysis can be obtained without harming the fetus, and an adequate time period is available for completion of necessary genetic and biochemical studies soon enough for elective abortion, if necessary.
A physician extracts amniotic fluid from the womb. The fluid will be examined to determine the health of the fetus.
Amniocentesis also is utilized as a method for assessing the well-being and maturity of a fetus. In such cases, the procedure is carried out later in the pregnancy and may be repeated at appropriate intervals, when needed. For example, amniocentesis is required to assess fetal lung maturity when fetal respiratory distress syndrome is suspected. Modern amniocentesis, even where repeated, is relatively simple and is reported to result in a risk factor of less than 1 percent for mother and fetus.
Amniocentesis is carried out in several steps. First, the placenta is located by the use of ultrasound techniques. Then, the participating physician locates the fetus by abdominal palpation. Next, the expecting mother is given a local anesthetic and a 20-gauge needle is inserted carefully into the amniotic sac. As soon as amniotic fluid is seen, a 20 milliliter sample (about four teaspoons) is drawn into a hypodermic syringe and the syringe is removed. Amniocentesis is reported to be painless, and most patients feel only a little abdominal pressure during the procedure.
The amniotic fluid of early pregnancy resembles blood serum. As pregnancy continues, its content of substances from fetal urine and other fetal secretions increases. The fluid also contains fetal cells from skin, gastrointestinal, reproductive, and respiratory tracts. Therefore, it is of great diagnostic use. Immediately after the fluid is removed from the fetus, the fetal cells are separated out. Then, the cells are used for genetic analysis, and the amniotic fluid is examined by various biochemical techniques.
Many other problems caused by abnormal biochemical events can be assessed by the use of amniocentesis. Advanced maternal age—pregnancy in women over thirty-five—is viewed by many as a leading basis for prenatal analysis by amniocentesis. The primary fears are chromosomal disorders; these diseases can be diagnosed by examination of fetal cells cultured from samples taken by amniocentesis. A particular fear is Down syndrome and its resultant severe mental disability.
Other diseases that can be identified by similar chromosomal analysis include spina bifida, ancephaly, and Klinefelter’s syndrome. Several of these disorders can be corrected while the fetus is still in the uterus, if diagnosed early enough. Where such treatment is not possible, the diagnosis makes it possible to identify the need for therapeutic abortion on the basis of the genetic data. Therefore, amniocentesis can be a very useful tool.
While some practitioners report that amniocentesis has been used since the 1920’s, Douglas Bevis is credited widely as doing landmark research in the area. This endeavor was reported on February 23, 1952, when Lancet published a study called “The Antenatal Prediction of Hemolytic Disease of the Newborn.”
For thousands of years, the inability to see or touch a fetus in the uterus was a staggering problem in obstetric care and in the diagnosis of the future mental and physical health of human offspring. With Bevis’s report in 1952, all this changed.
In the years that have followed Bevis’s original observation, many improvements in the methodology of amniocentesis and the techniques used in the genetic and biochemical information obtained have led to refinement of outcomes of its use. Hundreds of debilitating hereditary diseases can be diagnosed by—and some can be ameliorated as a result of—the examination of amniotic fluid and fetal cells isolated by amniocentesis. For many parents who have had a child with some hereditary disease, the use of the technique has become a major consideration in family planning. Furthermore, many physicians recommend strongly that all mothers over the age of thirty-four be tested by amniocentesis.
According to many researchers in the field, the basis for use of amniocentesis and prenatal analysis by “older” mothers is the larger number of at-risk children that are born. For example, more than 50 percent of babies born with Down syndrome are born of women who become pregnant at age thirty-five or older.
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Bevis, Douglas C. A. “The Antenatal Prediction of Hemolytic Disease of the Newborn.” Lancet 1 (February 23, 1952): 395-398. Describes Bevis’s original work on amniocentesis, and discusses the procedure’s medical implications. -
Filkins, Karen, and Joseph F. Russo. Human Prenatal Diagnosis. 2d ed. New York: Marcel Dekker, 1990. An attempt to “clarify and rationalize aspects of diagnosis, genetic counseling, and intervention.” Can be used as a guide to health professionals who care for pregnant women. Fourteen chapters by experts in the field cover topics such as DNA analysis. -
Milunsky, Aubrey. The Prenatal Diagnosis of Hereditary Disorders. Springfield, Ill.: Charles C Thomas, 1973. Details the practice and use of amniocentesis, chromosomal/sex-linked and biochemical hereditary disorders, congenital malformations, genetic counseling, and the implications of genetics to society. Includes detailed listings of the basis for many hereditary diseases and almost nine hundred references. -
Rapp, Rayna. Testing Women, Testing the Fetus: The Social Impact of Amniocentesis in America. New York: Routledge, 1999. Part of the Anthropology of Everyday Life series, this work analyzes the social and cultural aspects of amniocentesis and the diagnosis of fetal abnormalities. Includes a bibliography and an index. -
Reed, George B., Albert E. Claireaux, and Murray D. Bain, eds. Diseases of the Fetus and Newborn: Pathology, Radiology, and Genetics. St. Louis, Mo.: C. V. Mosby, 1989. This authoritative and detailed text is aimed primarily at physicians. Nevertheless, it contains many topics of use to other qualified readers, including exposition of many related disease processes, description of the pathology of the main body systems, radiologic methods, and many topics in medical genetics and prenatal diagnosis. -
Tucker, Susan M., and Sandra Bryant. Fetal Monitoring and Fetal Assessment in High-Risk Pregnancy. St. Louis, Mo.: C. V. Mosby, 1978. This book highlights many important aspects of fetal monitoring and includes descriptions of equipment, methodology, and data. -
Verp, Marion S., and Albert B. Gerbie. “Amniocentesis for Pre-Natal Diagnosis.” Clinical Obstetrics and Gynecology 24 (1981): 1007-1021. This brief technical review of amniocentesis covers a wide area in a concise manner. Discusses counseling, composition of amniotic fluid, use of ultrasound, amniocentesis procedure, technical problems, and risks of amniocentesis. Includes seventy-five useful references.
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