gynecology and obstetrics
Preconception or Prenatal Carrier Testing of Parents
Introduction
Carrier testing is part of routine prenatal care and is ideally done before conception. The extent of carrier 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). Information should include the health status and presence of genetic disorders or carrier status of both parents, of first-degree relatives (parents, siblings, offspring), and of second-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. ). 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 ( General references ). 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 ( (See also Prenatal Genetic Counseling .) 