Пренатальне генетичне дослідження батьків

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). 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). Diagnostic tests for specific abnormalities are offered to parents when appropriate (see table 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). 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).

After conception, pregnant women should be offered screening for fetal chromosome disorders using one of several methods. One method uses multiple maternal serum markers (alpha-fetoprotein, beta-human chorionic gonadotropin [beta-hCG], estriol, inhibin A) to detect neural tube defects, Down syndrome (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, and trisomy 13 is with analysis of cell-free DNA (cfDNA) in maternal plasma. Detection rates using this technology are higher than those with older methods.

(See also Prenatal Genetic Counseling.)