The roots of genetic counseling are often traced to prenatal diagnosis and reproductive decision making. Genetic counselors have been assisting women and couples with difficult reproductive choices for more than three decades. Typically, women referred for genetic counseling and prenatal diagnosis during pregnancy are those who are at increased risk of having a child affected by a genetic disorder. The most common indications are advanced maternal age (women >35 years of age), abnormal triple marker screening, abnormal ultrasound finding, or family history of an inherited condition.
All women are at risk to have a child with a chromosome abnormality or birth defect with every pregnancy; however, the chromosomal abnormality risk increases with age. At about the age of 35, a woman's risk to have a child with a chromosomal abnormality is roughly equivalent to the risk of a miscarriage from an amniocentesis (1 in 200 to 300). An amniocentesis is a standard procedure performed between 14 to 20 weeks of pregnancy to obtain a sample of amniotic fluid, which contains fetal cells that can be used for cytogenetic and molecular analysis. Another procedure called chorionic villus sampling (CVS), can be done earlier in pregnancy (10 to 12 weeks) to obtain fetal cells for testing.3 The miscarriage risk associated with CVS is slightly greater than that of amniocentesis at most centers. CVS is offered to women who know that they are at risk to have a child with a genetic condition so that diagnostic information can be obtained earlier in the pregnancy.
Genetic counselors in the prenatal setting explain the risk for genetic conditions due to maternal or paternal age, results from maternal serum screening tests, ultrasound findings, or family history. They present patients with prenatal diagnostic testing choices and discuss management and outcome options. Genetic counselors help patients make informed and autonomous choices through risk and procedure education, while also helping the patient to explore personal, spiritual, and cultural beliefs that affect decision making.4
The implementation of cystic fibrosis (CF) screening has caused a change in referral patterns for prenatal genetic counseling. A panel of experts convened for a National Institutes of Health consensus conference5 recommended that CF genetic testing be available to all adults with a positive family history of CF, a spouse or partner with CF, and all couples planning a pregnancy or seeking prenatal care. These recommendations were adopted by the American College of Obstetricians and Gynecologists and the American College of Medical Genetics with the development of laboratory standards and guidelines.6 In the majority of cases, patients are getting CF genetic testing without pretest counseling. When a patient has a positive result by the CF screening test, they are referred for posttest counseling to discuss the implications of the results, recurrence risk, and options for prenatal diagnosis. Some posttest counseling scenarios are complicated. For example, some asymptomatic individuals have compound heterozygous mutations associated with a milder CF phenotype. Chapter 10 discusses CF testing and genotype/phenotype associations in detail.
Other pregnancy-related indications for genetic counseling include advanced paternal age, history of infertility, recurrent pregnancy loss, and preconception counseling. Some couples, regardless of family history of a genetic condition, have taken a more proactive approach to family planning and request consultation with a genetic profes sional to discuss their risk of passing on a genetic condition to their children. Also, genetic carrier testing for disorders more common among individuals of Ashkenazi Jewish ancestry are in demand among couples presenting for preconception counseling and are now offered as a panel ranging from two to eight diseases, depending on the laboratory.
Preimplantation genetic diagnosis (PGD) offers couples who are at risk of having a child with a genetic condition an alternative to prenatal testing. Through in vitro fertilization (IVF), a single cell is removed from an embryo at the 8- to 16-cell stage and tested for the specific genetic condition or familial mutation; then the unaffected embryos are transferred back to the mother. PGD was first successful about a decade ago and is presently being offered for monogenic disorders and chromosome abnor-malities.7 However, it is not widely available as there are still many obstacles in the process related to the highly technical nature of the procedures and the difficulties in performing cytogenetic or molecular analysis on a single cell. The rate of pregnancy among patients undergoing IVF and PGD varies but rarely exceeds about one third.8 Genetic counseling for couples considering PGD is imperative. Couples need to understand the risks and benefits of these complex procedures and the likelihood of a successful pregnancy. Couples need to weigh these factors against those of standard prenatal diagnosis procedures. PGD also is very expensive and not covered by most healthcare coverage providers.
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