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Prenatal Genetic Testing of Parents

By

Jeffrey S. Dungan

, MD, Northwestern University, Feinberg School of Medicine

Medically Reviewed Oct 2022
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Genetic testing is part of routine prenatal care and is ideally done before conception. The extent of genetic testing is related to how the woman and her partner weigh factors such as

  • The probability of a fetal abnormality based on risk factors and the results of any previous testing

  • The probability of a complication from invasive fetal testing

  • The importance of knowing the results (eg, would the pregnancy be terminated if an abnormality was diagnosed, would not knowing the results cause anxiety)

For these reasons, the decision is individual, and recommendations often cannot be generalized to all women, even those with similar risk.

A screening history is part of the evaluation. The history is summarized as a pedigree (see figure Symbols for constructing a family pedigree Symbols for constructing a family pedigree Symbols for constructing a family pedigree ). Information should include the health status and presence of genetic disorders or carrier status of both parents, of 1st-degree relatives (parents, siblings, offspring), and of 2nd-degree relatives (aunts, uncles, grandparents), as well as ethnic and racial background and consanguineous matings. Outcomes of previous pregnancies are noted. If genetic disorders are suspected, relevant medical records must be reviewed.

Genetic screening tests for potential parents are best done before conception. Traditionally, tests are offered to parents at risk of being asymptomatic carriers for certain common mendelian disorders (see table Genetic Screening for Some Ancestries Genetic Screening for Some Ethnic Groups Genetic Screening for Some Ethnic Groups ). Diagnostic tests for specific abnormalities are offered to parents when appropriate (see table Indications for Fetal Genetic Diagnostic Tests Indications for Fetal Genetic Diagnostic Tests Indications for Fetal Genetic Diagnostic Tests ). Because parent ethnicity is often complex and not well-defined and because prenatal genetic testing is becoming much less expensive and quicker, some clinicians are starting to screen all potential (and expectant) parents, regardless of ethnicity (called universal carrier screening). Therefore, current approaches to carrier screening include offering all patients the same larger list of conditions to be evaluated. Often, dozens of genes and disorders (some with more severe phenotypic consequences than others) are included (1 General references Genetic testing is part of routine prenatal care and is ideally done before conception. The extent of genetic testing is related to how the woman and her partner weigh factors such as The probability... read more ). Increasing the amount of testing and evaluation is expected to increase the complexity of pre-test counseling. The American College of Medical Genetics and Genomics recommends a tiered carrier screening system based on carrier frequency and has provided tables listing disorders to be included in carrier screening panels (2 General references Genetic testing is part of routine prenatal care and is ideally done before conception. The extent of genetic testing is related to how the woman and her partner weigh factors such as The probability... read more ).

After conception, pregnant women should be offered screening for fetal chromosome disorders using one of several methods. One method uses multiple maternal serum markers Maternal serum screening for neural tube defects Noninvasive maternal screening, unlike invasive testing, has no risk of test-related complications. By more precisely assessing the risk of fetal abnormalities, noninvasive maternal screening... read more Maternal serum screening for neural tube defects (alpha-fetoprotein, beta-human chorionic gonadotropin [beta-hCG], estriol, inhibin A) to detect neural tube defects Maternal serum screening for neural tube defects Noninvasive maternal screening, unlike invasive testing, has no risk of test-related complications. By more precisely assessing the risk of fetal abnormalities, noninvasive maternal screening... read more Maternal serum screening for neural tube defects , Down syndrome Down Syndrome (Trisomy 21) Down syndrome is an anomaly of chromosome 21 that can cause intellectual disability, microcephaly, short stature, and characteristic facies. Diagnosis is suggested by physical anomalies and... read more Down Syndrome (Trisomy 21) (and other chromosomal abnormalities), and some other birth defects. This screening is called analyte screening. It is done at 15 to 20 weeks of pregnancy. An increasingly popular method of screening for fetal Down syndrome, trisomy 18 Trisomy 18 Trisomy 18 is caused by an extra chromosome 18 and is usually associated with intellectual disability, small birth size, and various congenital anomalies, including severe microcephaly, heart... read more Trisomy 18 , and trisomy 13 Trisomy 13 Trisomy 13 is caused by an extra chromosome 13 and causes abnormal forebrain, midface, and eye development; severe intellectual disability; heart defects; and small birth size. Diagnosis is... read more Trisomy 13 is with analysis of cell-free DNA 1st-Trimester Screening Noninvasive maternal screening, unlike invasive testing, has no risk of test-related complications. By more precisely assessing the risk of fetal abnormalities, noninvasive maternal screening... read more 1st-Trimester Screening (cfDNA) in maternal plasma. Detection rates using this technology are higher than those with older methods.

General references

Fetal genetic diagnostic tests

Tests are usually recommended if risk of a fetal chromosomal abnormality is increased (see table Indications for Fetal Genetics Indications for Fetal Genetic Diagnostic Tests Indications for Fetal Genetic Diagnostic Tests ). Fetal genetic diagnostic tests, unlike screening tests, are usually invasive and involve fetal risk. Thus, in the past, these tests were not routinely recommended for women without risk factors. However, because fetal genetic diagnostic tests are now more widely available and safety has improved, offering fetal genetic testing to all pregnant women, regardless of risk, is recommended. Array comparative genomic hybridization in prenatal testing is most frequently used to evaluate fetuses with structural abnormalities. Arrays detect numeric chromosome abnormalities (eg, trisomies) as well as unbalanced structural chromosome disorders, such as microdeletions. Studies have reported about 6% incidence of array abnormalities that would have been missed with traditional karyotyping in structurally abnormal fetuses.

Table
Table

Drugs Mentioned In This Article

Drug Name Select Trade
Novarel, Ovidrel, Pregnyl
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