Prenatal Genetic Screening

  • Stanley S. Grant, MSN, RN, CGC
    Stanley S. Grant, MSN, RN, CGC

    Stanley S. Grant, MSN, RN, CGC, is an Advance Practice Nurse at the University of Iowa Hospitals and Clinics. She is the nurse coordinator of the Prenatal Genetics Clinic and the Fetal Diagnosis and Treatment Unit in the Department of Obstetrics and Gynecology. She was involved in the planning and implementation of the Iowa Expanded MSAFP Screening Program at its beginning in 1987 and has acted as the nurse coordinator since that time. For over 20 years, she has provided counseling and care for women considering and undergoing prenatal diagnosis and screening. She is certified as a genetic counselor by the American Board of Medical genetics and is a founding member of the International Society of Nurses in Genetics (ISONG). Major interests include the impact of prenatal diagnosis on women and their families and supporting the role of nurses in providing genetic services.


This article presents a discussion of screening principles and techniques available to screen for common birth defects during pregnancy. Sixty-five to 70% of women have serum screening and /or ultrasound during pregnancy to evaluate the health and well-being of the developing fetus. The most common birth defects identified by screening include neural tube defects and chromosome abnormalities. Nurses employed in prenatal care settings need to have accurate information they can provide to women so they understand the benefits and limitations of screening. Timely presentation of information and identification of available resources will help nurses minimize confusion and provide support for women as they proceed with pregnancy screening.

Key Words: Screening, AFP, Down syndrome, neural tube defect, false positive


Modern childbearing has brought with it new and expanding reproductive testing options that provide women with previously unavailable information about their pregnancies. Of the three to four percent of babies born with recognizable birth defects most are born in families without identified risk factors (Kalter & Warkany, 1983a & 1983b). Because women are concerned about the health and well-being of the fetus, prenatal screening and/or diagnosis is offered to all women early in pregnancy. About 70% of women in the United States have maternal serum screening and/or ultrasound to detect risks for common birth defects during their pregnancy (Palomaki, Knight, McCarthy, Haddow, & Donhowe, 1997; Filly, 2000).


Screening in both clinical and community contexts is promoted as a cost-effective means of identifying individuals who have an increased risk for disease and is an important component of public health efforts (Croyle,1995). There is, however, considerable confusion and misunderstanding that surrounds screening techniques. A

A screening test does not give a yes or no answer but identifies increased risk for certain disorders so that definitive diagnostic tests can be offered.

screening test does not give a yes or no answer but identifies increased risk for certain disorders so that definitive diagnostic tests can be offered. Screening is targeted at apparently healthy individuals who are not aware of symptoms. Screening limits the number of people who have to undergo diagnostic tests that may be expensive or have an element of risk associated with them. After subsequent diagnostic tests have identified those who have the condition, treatment is started to lessen the effects of the condition or to prevent it from developing (Armitage & Colton, 1998). Most individuals called positive by screening are false positive. That is, although the screening test is positive, the diagnostic test will be negative for the condition. False positives relate to the specificity of the test. The number of true positives, people who are found to actually have the condition, are small compared to the number of false positives (Dwyer, 1983).

Prenatal Screening

Prenatal screening as we know it today could only follow the development of accurate prenatal diagnosis. Procedures to safely obtain fetal tissue and laboratory tests that could accurately diagnose specific conditions in the fetus have been available since the early 1970's. The first such procedure, amniocentesis, was primarily offered to women over age 35 at delivery to diagnose chromosome abnormalities in the fetus and to those in families at risk for conditions that were amenable to prenatal diagnosis. Although prenatal testing is thought of as genetic

A fundamental difference between prenatal and other types of screening is that when prenatal screening leads to the diagnosis of an abnormality in the fetus there is frequently no treatment available before birth.

testing, there are many birth defects for which it is far from definitive and even misleading to refer to them as genetic disorders (Duster, 1990). Many of the more common birth defects belong to a category of disorders with a multifactorial or polygenic cause. This type of inheritance involves an interaction between genes and environmental factors. Neural tube defects such as spina bifida are an example of multifactorial inheritance. Other conditions such as chromosome abnormalities like Down syndrome are genetic in that they affect the genetic makeup of the individual but not in the sense that they are usually inherited from a parent. There are other birth defects that may be due to exposures to medication or other agents that alter the genetic expression but are not due to intrinsic genetic factors in the fetus or the mother. As the work of the Human Genome Project continues there will be a greater number of genes identified that may be screened in adult populations. The issues surrounding prenatal screening for genes that are associated with adult onset conditions or predispositions are yet to be fully debated and not part of a current clinical practice.

A fundamental difference between prenatal and other types of screening is that when prenatal screening leads to the diagnosis of an abnormality in the fetus there is frequently no treatment available before birth. Women are left with the choice between continuing the pregnancy knowing the infant will be born with the condition identified or abortion to prevent the birth of an affected child (Tymstra, 1991).

Screening by History

An important screening tool for assessing risk for birth defects is a review of family and personal health history before conception or at the beginning of pregnancy. Screening by this method is valuable but will not detect all birth defects. For example, two groups of common birth defects, neural tube defects and chromosome abnormalities, occur most often in families without identified risk factors.

It has been well established that the risk for Down syndrome (trisomy 21) and other chromosome abnormalities increases with advancing maternal age. Until the mid 1980's prenatal screening was primarily limited to women over age 35 at delivery who were offered the option of amniocentesis or chorionic villus sampling for diagnosis. About 20-30% of babies with Down syndrome are born to women in this age group. Because most women are having their babies when they are younger, the remaining 70 -80% of babies with chromosome problems, including Down syndrome, are born to women who are under age 35 (Haddow, et al., 1992).

The etiology of most neural tube defects is multifactorial, a complex interaction of genes and environment and not related to maternal age. In a small percentage of cases, the cause may be a chromosome abnormality or genetic syndrome with the neural tube defect as one of the manifestations of that condition. If screening and testing is offered on the basis of family history alone about 5% of cases will be identified. The other 95% of cases occur in families with no identified risk factors.

Neural tube defects

Neural tube defects are among the most common birth defects with an incidence of about 1/1000 in the United States. About 50% are anencephaly, a lethal condition where the brain and skull do not form properly. The other 50% are spina bifida. The survival rate and degree of physical and intellectual disability in children with spina bifida varies with the location and severity of the lesion and the treatment (Main, & Mennuti, 1986). There are some centers attempting to correct spina bifida by performing surgery on the fetus during pregnancy. It is too soon to know if these procedures will improve the outcome for children with this

Neural tube defects are among the most common birth defects with an incidence of about 1/1000 in the United States.


A discussion of neural tube defects would be incomplete without mentioning recent advances in the prevention. All woman of childbearing age should be counseled about the importance of folic acid. This vitamin is known to reduce the recurrence of neural tube defects in families who have had an affected child and to reduce the incidence in the general population (Medical Research Council, 1991; Czeizel, & Dudas, 1992). In the United States enriched rolls, buns, flour, farina, rice, macaroni products, and noodles are fortified with folic acid. Even with this supplementation most people do not get the recommended amount in their diet and supplementation is recommended. Not every neural tube defect will be prevented by taking folic acid but it is recommended that all women of childbearing age should take an additional 0.4 mgm of folic acid, available in nearly all multivitamins, to ensure optimal chances of prevention (Oakley, Adams, & Dickinson, 1996).

Down Syndrome

Down syndrome, also called trisomy 21, is the most common chromosome abnormality in live born infants. Children with Down syndrome have a characteristic appearance, hypotonia, and mental retardation. Congenital heart defects occur in about 40% of cases and are a major cause of death for individuals with this condition. The severity of the disorder and the degree of delay are not as evident in the infant as it is when the child grows older and begins to miss developmental milestones. Early support is essential for families and participation in infant stimulation programs is encouraged. There is no known cure for Down syndrome other than treatment of the health problems that may be more common for these children and adults (Lashley, 1998).

Laboratory Screening

The use of AFP or alpha-fetoprotein, is the first successful mass screening test for the prenatal detection of birth defects. Designed specifically to detect neural tube defects, it also identifies other structural malformations in the developing fetus. Alpha-fetoprotein is a fetal specific protein made first in the yolk sac and subsequently in the fetal liver. In 1972, Brock and Sutcliff demonstrated that open neural tube defects could be detected by transudation of alpha-fetoprotein into the amniotic fluid and across the placenta into the maternal serum. Pregnancy screening programs were developed and implemented in the United States in the early 1980's when the FDA approved the reagents used for this screening.

Neural tube defects can be detected by a combination of maternal serum screening, ultrasound and amniocentesis. A blood sample is drawn from the pregnant woman between 15 and 20 weeks gestation. The amount of AFP in the mother's blood is compared to the amount considered normal for that gestational age. If the levels of

Neural tube defects can be detected by a combination of maternal serum screening, ultrasound and amniocentesis.

AFP are high, evaluation of the pregnancy may include a repeat blood test, an ultrasound to look for an explanation for the elevated levels of AFP and sometimes amniocentesis. Maternal serum alpha-fetoprotein (MSAFP) screening will detect 85% of neural tube defects. About 1 in 30 women who have two elevated AFP's will have a fetus with a neural tube defect (Burton, 1998). Other conditions associated with elevated levels of AFP include the following: a) inaccurate gestational dating, b) multiple gestation, c) miscarriage, d) abdominal wall or other structural defect, and e) placental pathology that may result in a pregnancy complication such as growth restriction, placental abruption, or symptoms related to placental insufficiency. A level II ultrasound and evaluation by an obstetric or perinatal specialist will provide a comprehensive examination and counseling for the family.

In 1984, Merkatz, Nitowsky, Macri, and Johnson demonstrated that sera of women carrying fetuses with Down syndrome had lower levels of AFP. In 1986 a collaborative study was completed in the New England region of the United States using maternal serum AFP and maternal age to screen pregnancies of women under age 35 for Down syndrome (Palomaki, 1986). Levels of AFP are about 25% lower in pregnancies where the fetus has Down syndrome. Risk for Down syndrome was then calculated with a formula using AFP and maternal age. Women under age 35 with a calculated risk for Down syndrome comparable to the risk of a 35 year old (1/270) or greater were offered amniocentesis for diagnosis. The protocol identified about 40% of cases of Down syndrome in this age group (Palomaki, Williams, & Haddow, 1989).

Work by other researchers (Bogart, Pandian, & Jones, 1987) (Canick, et al., 1988) resulted in the addition of estriol and human chorionic gonadotrophin to screening protocols. Wald, et al. (1998) predicted 60% of Down syndrome fetuses could be detected using these multiple markers in women across the age spectrum. Women found to have a risk of 1 in 190 or greater would be called screen positive and offered amniocentesis for definitive testing. With this approach 4-5 % of women would be called positive and 1/60 would be carrying a fetus with Down syndrome. Screening using multiple markers began in 1990 and the results of a prospective study in the New England region by Haddow and colleagues (1992) established the clinical effectiveness.

The desire to make screening more efficient has led investigators to evaluate other pregnancy hormones. If an analyte can increase screening efficiency without adding substantially to the cost, such changes are implemented. There is additional work that suggests that the addition of Inhibin A to the screening protocol may further enhance screening for Down syndrome either by lowering the false positive rate or increasing the detection rate (Cuckle, Holding, Jones, Groome, & Wallace, 1996; Aitken, et al. 1996). The addition of inhibin to the present three markers (AFP, estriol, and hCG), often referred to as the "Quad test", is being offered in some areas. Availability will increase as both reagents and hardware necessary to preform this test are perfected.

Screening by Ultrasound

The use of ultrasound in pregnancy has increased dramatically over the past three decades. It is now possible to evaluate fetal structure and growth and provide the clinician with information about the developing fetus. It may be used as a diagnostic test after an elevated MSAFP to look for spina bifida or other structural birth defects. When used by experienced operators, prenatal ultrasound is sensitive and specific enough for the diagnosis of neural tube defects (Lennon & Gray, 1999). Amniocentesis is still necessary when an adequate examination of the fetus is not possible, when another indication such as maternal age is present or when an abnormality is detected. Although spina bifida is usually an isolated birth defect, when it is present as the result of a chromosome abnormality the prognosis for the fetus is very different. Amniocenteses will accurately diagnose chromosome abnormalities when they are present.

When used by experienced operators, prenatal ultrasound is sensitive and specific enough for the diagnosis of neural tube defects

Ultrasound may also be used as a screening test in low risk women. Use of this technology can determine gestational age with a high degree of accuracy in the first and second trimester, the presence of multiple gestation, monitor growth patterns in the fetus, and confirm the location of the placenta. There are, however, ultrasound findings that are of little significance alone but can be associated with chromosome abnormalities. There are a number of markers that may indicate an increased risk for Down syndrome and other chromosome abnormalities. These include: a) structural anomalies of the hands, face, or heart, b) short femur, humerus, or ear, c) pyelectasis, d) echogenic bowel, e) choroid plexus cysts, f) two vessel cord g) and echogenic foci in the ventricle of the heart (Vintzileos, Smulian, Day-Salvatore, & Knuppel, 1999). The initial research that evaluated these findings was done in women at high risk because of maternal age or an abnormal serum screening test. The presence or absence of these markers was used to modify risk and to help the woman decide if she desired invasive testing with the attendant risks. It is unclear whether these markers are accurate enough in low risk populations to warrant the invasive tests necessary to make a definitive diagnosis. Women having ultrasound for other reasons may find themselves confronted with questions about the health of the fetus that can only be answered by doing additional tests (Filly, 2000). Serum screening can be offered to women who are between 15 and 20 weeks gestation to provide information that will further clarify the risk for Down syndrome or another chromosome abnormality, trisomy 18.

Women who choose to have ultrasound specifically to diagnose conditions such as neural tube defects or Down syndrome must understand the limitations of this form of testing. It is possible to miss small neural tube and other structural defects. A fetus with a completely normal ultrasound exam can still be affected with Down syndrome and perhaps 50% of cases will be missed relying on ultrasound alone for diagnosis. Counseling about the limitations of ultrasound evaluation is an important aspect of this approach (Bahado-Singh, et al., 1998; Vintzileos, Guzman, Smulian, Mclean, & Ananth, 1997).

First Trimester Screening

There has been a great deal of interest in establishing screening in the first trimester of pregnancy. It is hoped that the psychological stress of identifying an affected pregnancy is less severe if the diagnosis is made in early pregnancy. An early diagnosis gives parents more time to adjust to the fact that the child will have special health needs and to prepare for delivery and the newborn period. For families who choose pregnancy termination, procedure related risks are lower in the first trimester. The most promising maternal serum analytes for use in the first trimester are a combination of either the intact molecule or free beta subunit of

The most promising maternal serum analytes for use in the first trimester are a combination of either the intact molecule or free beta subunit of hCG and the pregnancy associated plasma protein A (Papp-A)

hCG and the pregnancy associated plasma protein A (Papp-A). A prospective study in 1998 found that with these markers the detection rate for trisomy 21 in the first trimester equaled that of triple marker screening in the second trimester. This combination of first trimester markers has been recognized for several years but screening in the first trimester is not widespread. In 1998, Haddow et al. offered the following potential explanations. Chorionic villus sampling and early amniocentesis are not as widely available for follow-up diagnostic testing as midtrimester amniocentesis. Screening at this stage of pregnancy does not allow for evaluation of neural tube defects. The ultrasound for gestational dating to make first trimester screening as sensitive as screening in the second trimester would add to the cost of screening. As of 1998 when Haddow wrote the paper, the assay for (PAPP-A) was not licensed in the United States. There are some women who will miss the opportunity for first trimester screening because they do not start prenatal care soon enough.

During the recent decade an increasing body of knowledge has developed related to an ultrasound finding in the first trimester. Increased nuchal translucency, caused by the subcutaneous accumulation of fluid behind the neck of the fetus indicates an increased risk for chromosome abnormalities including Down syndrome (Nicolaides, Azar, Byrne, Mansur, & Marks, 1992; Schulman, et al., 1992). By combining ultrasound measurement of the nuchal translucency with maternal age it is possible to identify pregnancies at increased risk for chromosome abnormalities and some congenital heart defects. These women can then be offered chorionic villus sampling or amniocentesis for definitive diagnosis of chromosome abnormalities. If the chromosome evaluation is normal, another ultrasound is performed in the second trimester to exam the fetal heart and other organs. When combined with maternal age and appropriate maternal serum biochemistry some have reported a sensitivity of almost 90% with a false positive rate of 5% (Nicholaides, Sebire, & Snijdes, 1999). This form of screening requires skilled operators and is prone to operator variability. Questions relating to the skill of the individuals performing and interpreting ultrasound exams continue to raise concern. A number of studies have shown that with appropriate training and high motivation sonographers can learn to do this measurement with acceptable accuracy. Standardized methods and criteria will increase the repeatability and reliability (Braithwaite, et al., 1996).

The potential to diagnose fetal abnormality by examining fetal cells found in maternal circulation has been studied for 30 years. Diagnosis of biochemical, DNA, and chromosome abnormalities may be possible. The type of fetal cell to examine and the most efficient way to harvest, sort, and analyze them is under investigation. Limitations exist because some types of fetal cells can remain in the maternal circulation from previous pregnancies. Until the technology improves, this type of evaluation will remain a screening test requiring amniocentesis or chorionic villus sampling necessary for definite diagnosis (Wright, 1994; Nicolaides, et al., 1999).

Psychological Aspects of Screening

Researchers have documented the psychological costs of screening during pregnancy (Marteau, 1989; Evans, et al., 1988; Abuelo, Hopmann, Barsel-Bowers, & Goldstein, 1991; Marteau, et al., 1992). A significant level of anxiety is present for women with a positive screening test result. The anxiety may persist throughout the pregnancy even when subsequent diagnostic tests are normal.

Often women do not have enough information about tests before they are asked to make a decision about screening (Marteau, et al., 1992). There are several aspects of screening that make education difficult for both clinicians and patients. Screening protocols are complex and evolving. Details such as the number of markers analyzed and the cut-offs for calling a test positive may vary between laboratories and in the same laboratory over time. The practice of reporting results as a ratio of 'one-in-something' seems to cause difficulty understanding what the result means to a particular woman. The fact that the result is based on information about the current pregnancy may serve to increase anxiety as well. The pregnancy is not at risk because of a population risk factor such as age but because of factors specific to this woman and this baby (Green & Statham, 1999). The anxiety that is engendered by a positive test often makes the subsequent counseling and explanation difficult for the woman to process. The perceived threat to the developing fetus coupled with the feeling of helplessness as the diagnostic process continues outside her control may serve to intensify this reaction for the pregnant woman.

Many women participate in screening for reassurance, seeking the psychological benefit of a reassuring negative test result.

The reasons many women accept screening may be at odds with or at least different from, the reason practitioners suggest testing. Farrant (1985) found that the majority of women sought screening for reassurance in contrast to their obstetricians who were primarily screening to detect abnormality. This may explain why many women find themselves unprepared for their reaction when a test is called positive. Another factor that influences women's acceptance of screening is the fact that the testing is seen or presented as routine. Tests that are routine are assumed to be necessary and appropriate (Green & Statham, 1999). When an abnormal test results in the offer of invasive testing with potential harm to the fetus and a situation that confronts a decision about abortion, it leaves many women angry and confused. The decision to participate in pregnancy screening is ultimately one that is made by the woman based on her own values and beliefs and the information she receives both from her provider and from sources such as friends, family, and media.

For most women the diagnostic tests that follow a positive screening test result will not reveal a birth defect and the pregnancy will progress uneventfully. Some women continue to be concerned about the baby even when follow up examinations are normal. A screening test result that cannot be completely explained results in additional stress for the family. An example is an elevated MSAFP when screening for neural tube defects. The woman can be reassured about the presence or absence of a birth defect by having an ultrasound and/or amniocentesis. The increased risk for pregnancy complications related to placental pathology requires additional surveillance and this concern is not resolved until the birth of the baby. Another example is the incidental finding of a subtle ultrasound abnormality such as a dilated ventricle discovered at the time an amniocentesis is being performed after an abnormal screening test for Down syndrome. The chromosome test can rule out Down syndrome but uncertainty about the meaning of the dilated ventricle remains until the baby can be examined after birth.

A great deal of attention is focused on the woman who has a screening test that is false positive. There are also false negative results associated with screening. Many women participate in screening for reassurance, seeking the psychological benefit of a reassuring negative test result. Maternal serum screening will detect 85% of open neural tube defects and over 60% of Down syndrome which means that 15% and 40% respectively will be missed. These patients will have a "normal" test result but the fetus will have the condition. That is, the test is negative even though the condition being screened for is present. A screening test cannot be 100 % reassuring because of the distinction between a screening and diagnostic test. The first systematic attempt to document the psychological consequences of false negative results from Down syndrome screening was reported by Hall, Bobrow, & Marteau in the UK (2000). They documented that some parents who receive false negative results from Down syndrome screening may experience anger and a small adverse affect on parental adjustment. Additional studies are needed to evaluate ways of reducing or avoiding poor adjustment to the child.

Attitudes related to abortion are important issues to discuss both in terms of providing accurate information about pregnancy termination and to allow the woman to explore her personal feelings. Because many women view the testing as an opportunity for reassurance that the fetus is developing normally, they may accept screening in spite of a belief that they would not have an abortion if the fetus is affected. Others want to have the opportunity to prepare themselves for the birth of a child with serious health problems. Some families are sure pregnancy termination is an option they will consider. Many women are not certain how such information will affect their decision to continue the pregnancy and accept screening hoping for a normal result so they will not have to make such a decision.

The Nurse's Role in Explaining Screening

Nurses may participate in screening in a number of ways. They may be involved in planning, implementing, administering or evaluating screening and testing programs or they may care for patients undergoing or considering screening. It is important for nurses in direct patient care to be aware of the availability and potential impact of screening techniques. This will allow them to provide appropriate information and support at each step in the process so that attendant psychological costs are minimized. Basic understanding of screening principals is important for all nurses but more in-depth knowledge of pregnancy screening is required for nurses in prenatal care practice settings.

Informed consent is the first step in the screening process. Pregnancy screening is voluntary; and although it is standard of care to offer screening, it may be refused. It is important for nurses to educate themselves so they can provide accurate and sensitive answers to the following questions.

What are the conditions for which the test is designed to detect increased risk?

In the case of pregnancy screening most tests are designed to detect birth defects such as spina bifida, anencephaly, abdominal wall defects, and chromosome abnormalities. Some of these conditions may be unfamiliar to the patient. Written information about the tests and the conditions being screened for should be available to supplement the discussion about the test.

What are the steps that will be suggested if the screening test is positive?

Nurses offering screening should help the patient understand that the blood test may be only the first step and other tests will be offered if the screen is abnormal. The other tests may include both ultrasound and amniocentesis. Nurses should be able to provide information about the availability of such procedures, how and when they would be scheduled, and where to find additional information about them.

Some of the conditions that may benefit from prenatal diagnosis include heart defects, neural tube defects, abdominal wall defects and chromosome problems.

This is the time to explore what the screening will mean for the family in the context of their personal values and beliefs. Discussions about abortion may occur at this time. There is no treatment available during pregnancy for most of the conditions being screened. Abortion is an option that women have questions about and accurate information about abortion services should be available. Some practitioners feel that if a woman would not consider abortion that it is of less value to offer screening. It is important to remember that there is benefit in knowing about a serious birth defect even when treatment before birth is not available. Screening that results in the diagnosis of a serious birth defect will allow for planning delivery at a center where appropriate care is available. Having time before delivery to meet consultants and make decisions about treatment options for the newborn is important to many families who learn that the baby will be born with serious or lethal health problems. Some of the conditions that may benefit from prenatal diagnosis include heart defects, neural tube defects, abdominal wall defects and chromosome problems (O'Connor, 1997).

What are the patient's reasons for accepting or rejecting screening?

A young, healthy woman may believe that because her population-based risk for chromosome abnormalities is small that she is not at any risk for an abnormality. Women over age 35 may look to screening as a way to avoid the risks of invasive testing. This is the age group most likely to refuse amniocentesis after a positive serum screening test fails to remove them from the at-risk category (Fitzgerald, Streets, & Priest, 1992). The nurse can help the family explore the potential outcome of the decision to accept or decline screening.

Concern about any harmful effects of exposures to medications or environmental agents may lead some women to accept screening. It is important to clarify what is known about specific agents so that the testing is not being accepted hoping to gain information that screening cannot provide. There are resources that help the practitioner provide this information but it may be necessary to refer some families to specialists for adequate evaluation and counseling.

For specific family history factors, it may be more appropriate to forego screening and refer the woman for more in-depth evaluation and consideration of diagnostic testing. It is optimal to assess family and personal health before pregnancy so that appropriate diagnostic tests and complex evaluations can be completed. This is not always possible, as some women do not address these risk factors until they are pregnant. Early prenatal visits for review of history and health problems may prevent missed opportunities for early screening or diagnosis. It also gives the woman time to discuss testing with her partner and others who may be important in the decision to accept screening.

When should the decision about accepting screening be made?

There is a specific screening time window when the blood can be drawn and accurately evaluated for prenatal serum screening. Patients need to understand when testing is most accurate and when the screening window closes. First trimester screening is generally offered from 11 to 14 weeks and 2nd trimester screening between 15 and 20 weeks. The patient should know the specific details of the testing process such as where and when to have the blood drawn and how long it takes to complete the test and report the results. Pregnancy screening protocols vary and it may be difficult to determine the best choices for a particular woman. Nurses should have resources identified for those patients who have questions that are beyond their expertise.

What information does the laboratory need to evaluate this sample?

When women elect to have screening it is important to furnish the laboratory with the most accurate available information about the patient and the pregnancy. The wrong gestational age, maternal age or weight can make a test falsely positive or negative. A discussion about the date of the last menstrual period, the woman's menstrual cycle and how this compares to other information such as early ultrasound will help to insure that mistakes in gestational dating are avoided. Factors such as maternal diabetes and family history of neural tube defects may affect the analysis of the screening test as well.

How does the patient want to find out the results of the test if they are normal? If they are not normal?

This is the time to discuss how and when the results of the blood test will be reported to the patient. A telephone call or letter in the mail is adequate to report negative results. A discussion should take place at the next visit to review the meaning of a negative result as well. If the results are not normal, it is important to determine how the woman would like to hear the results. A telephone call at the work place may cause problems if some thought is not given to the environment. The potential intense emotional response to a positive test makes it important to give those who are at work the opportunity to find privacy for the discussion. It is important to emphasize again that positive test results do not mean that the baby has a birth defect. Only additional testing will make such a diagnosis.

Screening Follow-up

When additional tests or a referral to a specialist is indicated, appointments should be made at the earliest convenience for the patient. Emphasize that the woman has time to consider any testing offered and she does not have to make decisions about accepting invasive testing or about pregnancy termination until she has adequate information. An appointment for further discussion with the primary provider should be offered. At a minimum the woman will need a telephone number and contact person so that when she discusses the result with her partner or additional

Emphasize that the woman has time to consider any testing offered and she does not have to make decisions about accepting invasive testing or about pregnancy termination until she has adequate information.

questions occur she has access to support and information. When a woman has a positive screening result it is not uncommon for her to go to family, friends, and the Internet for additional information about the conditions being screened. A review of this information to determine if it is being interpreted accurately in relation to the patient's specific situation will help prevent confusion.

Nurses will not have in-depth knowledge about every aspect of pregnancy screening. Each nurse working in settings where pregnancy screening is offered should establish their own network of resources for themselves and for their patients. This can include resources within the screening laboratory, perinatal centers where Level II ultrasound and diagnostic testing are performed, genetic counseling resources and support groups for families with birth defects and perinatal losses. Such resources will help the nurse to provide the most appropriate risk assessment, information and support for patients (Wright, 1994). Follow up contact with the family after appointments with consultants will help the nurse to stay informed and provide support for the woman who may be waiting for the results of additional testing.

For women who have negative results on the screening test the nurse should confirm that the patient received the results and is interpreting them accurately. It is still necessary to continue routine prenatal care and to realize that the test result does not mean the baby is normal in every way

The women who have screen positive results that lead to normal diagnostic tests may need additional support throughout the rest of the pregnancy. An assessment of emotional well-being may identify women who will benefit from additional counseling and support. This is the group of women who can teach the nurse the most about their own practice. Ask these women if the results were reported in a timely way and if questions were adequately answered. If the nurse discovers deficiencies that are common in the women with positive test results, it will allow them to seek education and resources in that area and to make changes that improve practice.

The care of women who have an abnormality detected after a positive screening test is beyond the scope of this discussion. Often women in this circumstance will complete pregnancy care in a high risk setting although there are some who will return to the primary care practice on a shared care basis. The special needs of this patient population are usually managed in a high-risk setting.

Case Studies

The following two case studies illustrate how nurses can provide care for prenatal patients undergoing screening. Each case study will be followed by a discussion.

Case Study 1

Mary V. is a 38 year old woman who begins prenatal care early in the first trimester of her second pregnancy. Her first pregnancy ended at 8 weeks with a spontaneous abortion. After several years of trying to conceive, Mr. and Mrs. V. sought infertility treatments and have achieved a pregnancy after In Vitro fertilization. The treatments cost over $10,000 and the couple comment on more than one occasion that after spending so much money to conceive they will not subject the pregnancy to avoidable risk. They feel certain that they would not terminate a pregnancy because of Down syndrome but remain concerned about the risks of other fetal chromosome abnormalities related to maternal age. They also desire to experience a pregnancy that is as normal as possible and want to deliver in their local community. Their primary care provider is knowledgeable about the risk for chromosome problems related to maternal age and about the common methods of prenatal diagnosis. The information about some of the newer screening tests for chromosome abnormalities is not as familiar and the patient is referred to a perinatal center with expertise in pregnancy screening and diagnosis. The V.'s elect to have a nuchal translucency measurement at 11 weeks. The measurement is not increased and the risk for Down syndrome is determined to be less than the patient's age-related risk. She chooses to forgo invasive testing at this time but elects to have second trimester serum screening to further evaluate risk. Although the Quad test is only available in a few selected areas of the country, a laboratory is located and blood is sent for evaluation. The result of this test is reported as screen positive with a risk for Down syndrome of 1/148 that is still less than her age related risk of 1/99. Mrs. V. again declines invasive testing. After discussion with the consultants an ultrasound evaluation of the fetal heart and other organs is scheduled as a final evaluation. When this exam is normal the V.'s continue the pregnancy without further evaluation and deliver a healthy baby at term.

Discussion of Case Study 1

This family demonstrates the approach and attitude of many women who are looking to screening to avoid the risks of invasive diagnostic testing. The only birth defects that increase in incidence with maternal age are chromosome abnormalities. If a woman is otherwise healthy and does not have medical conditions such as hypertension or diabetes, the pregnancy is likely to progress normally. There is a decline in fertility in this age group and many women seek evaluation and treatment from infertility specialists in order to conceive. It is not uncommon for couples in this situation to be very well informed about the newest and latest modalities for testing and screening. The nurse may learn about how these tests perform through this special group of patients. Insurance coverage may also become an issue, as newer tests may not be covered under every benefit package. During the pregnancy, the nurse in the primary care center can provide support for Mrs. V. and her husband as the couple goes through the screening process.

Case Study 2

Cheryl M. is a 19-year-old early in her first pregnancy. She is single, lives at home and is engaged to the father of the baby. The pregnancy is unplanned but both she and her boyfriend are happy. She lives in a small town and is seen for her pregnancy at a clinic established for low-income woman. An ultrasound is done around 10 weeks gestation because of an episode of vaginal bleeding. The ultrasound establishes her due date but offers no explanation for the bleeding. The bleeding continues off and on for the next two weeks and Cheryl is concerned that it may indicate a problem with the baby. She accepts screening hoping that the test will provide reassurance that all is well with the baby. The initial blood test comes back with a striking elevation of AFP and she is referred to a perinatal center for evaluation. The ultrasound at the center shows a fetus with an abdominal wall defect called gastroschisis. Cheryl is counseled about the condition and additional appointments are made with pediatric surgeons who will repair the defect when the baby is born. Delivery at the tertiary center is recommended because of the need for immediate treatment when the baby is delivered. Cheryl will continue her care in her local area and will return for ultrasounds and additional visits to the perinatal center as the time for delivery is near.

Discussion of Case Study 2

Gastroschisis is an explanation for an elevated maternal serum AFP. This is a repairable defect that will most often have a good outcome. This problem is seen more often in younger women (Rankin, Dillon, & Wright, 1999). It is not yet clear what factors may explain the increased incidence in this age group. The infant will, however, require major surgery and high risk care in the neonatal period. Much of the prenatal care can be provided in the local community with some visits to a medical center where the delivery will be planned. The visits often include referrals to the pediatric specialists who will care for the baby after birth. Parents often tour the pediatric units as well as the delivery room to prepare themselves and their family for the birth.


As Scanlon and Fibson note (1995):

"Genetics is becoming central to the delivery of health care and preventive services. Changes are occurring in the delivery of genetic services, with a gradual move from university-based genetics clinics to satellite genetics clinics and primary care settings. As these services move beyond specialized roles and settings, nurses in a variety of general practice areas have already or soon will confront the implications of the current advances in genetic science and technology" (p. 9). The importance of genetics in nursing practice and the desire for information about evolving genetic screening and technology makes accurate information necessary for nurses in many practice settings. Nurses who understand the screening process can help women make informed decisions about participating in screening. They can provide appropriate information and support throughout the testing process and help to interpret results. When results are abnormal or confusing the nurse can clarify when possible and identify resources to manage the stress and anxiety. Marteau, et al. said it best, "One of the greatest challenges for those involved in the screening process is to inform people of low probability but serious events without alarming them unduly or reassuring them falsely" (1992, p. 13). This skill will be increasingly important as additional screening tests are developed and introduced into practice.


Stanley S. Grant, MSN, RN, CGC

Stanley S. Grant, MSN, RN, CGC, is an Advance Practice Nurse at the University of Iowa Hospitals and Clinics. She is the nurse coordinator of the Prenatal Genetics Clinic and the Fetal Diagnosis and Treatment Unit in the Department of Obstetrics and Gynecology. She was involved in the planning and implementation of the Iowa Expanded MSAFP Screening Program at its beginning in 1987 and has acted as the nurse coordinator since that time. For over 20 years, she has provided counseling and care for women considering and undergoing prenatal diagnosis and screening. She is certified as a genetic counselor by the American Board of Medical genetics and is a founding member of the International Society of Nurses in Genetics (ISONG). Major interests include the impact of prenatal diagnosis on women and their families and supporting the role of nurses in providing genetic services.


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Citation: Grant, S. (September 30, 2000) "Prenatal Genetic Screening. Online Journal of Issues in Nursing" Online Journal of Issues in Nursing Vol. 5, No. 3, Manuscript 2.