Most prenatal and reproductive genetic counselors practice in the setting of a prenatal diagnosis program. The professional staff of a prenatal diagnosis program (physician, nurse, and genetic counselor) must obtain an accurate family history and determine whether other previously unsuspected genetic problems should be considered on the basis of family history or ancestry. Pretest and posttest counseling is recommended when genetic screening or testing is considered, including carrier screening, PGT, and prenatal screening and diagnosis.

For carrier screening and testing, until recently, ancestry was utilized to assess the need for carrier testing for a small number of X- linked or autosomal recessive conditions that are more prevalent in certain populations. Such disorders include thalassemias in individuals of Mediterranean or Asian background, sickle cell anemia in people of African descent, and various disorders that are more prevalent in people of Ashkenazi Jewish ancestry. Because it is becoming increasingly difficult to assign a single background to each individual, use of broader carrier screening panels, in which individuals are tested for a large array of genetic disorders irrespective of apparent or stated ancestry, is now recommended.

The complexities posed by the availability of so many different prenatal screening and testing options include the distinction between screening and diagnostic testing, the many different and distinctive indications for testing, the subtleties of interpretation of test results, and the personal, ethical, religious, and social considerations that enter into reproductive decision making. They make providing prenatal genetic services challenging, and prospective parents considering prenatal genetic screening or diagnosis should be provided with understandable information that will allow them to make informed decisions about which conditions to test or screen and whether they give or withhold consent for diagnostic procedures. Prenatal genetic counseling for women considering CVS or amniocentesis usually addresses several different points (see Box 1).

Box1. COUNSELING FOR CHORIONIC VILLUS SAMPLING OR AMNIOCENTESIS

Screening tests avoid the risk of a diagnostic procedure but do not give a yes/ no diagnostic answer. They provide a risk estimate for a disorder relative to the background risk. The cutoff for a positive screen is set to balance sensitivity and specificity, and screening tests generally allow higher false- negative rates than would be acceptable for a diagnostic test to keep false- positive rates to a reasonable level, generally below 5%. Advances in laboratory technology, both for screening and diagnostic tests, have led to testing options that are both more accurate and more expansive, providing information for a growing number of genetic conditions. This has made prenatal genetic counseling and parental decision making on which option to choose more complex. Although it is clear that cell- free DNA- based screening for Down syndrome is far more sensitive than maternal serum screening, we now know that CVS or amniocentesis coupled with CMA, a test that surveys the entire genome for aneuploidy and smaller imbalances (deletions and duplications), can detect a significant chromosomal abnormality in 1% to 1.7% of all pregnancies and in 6% of pregnancies with structural fetal abnormalities found on prenatal ultra sound. The latest data also support that amniocentesis and CVS are safer than previously thought. This has led to recommendations that this prenatal diagnostic test be offered to all women. Thus prenatal genetic counseling must inform women of all options and support them in decisions that balance their desire to know genetic information about their pregnancy with their willingness to undergo a procedure and the decisions they would make with this information.

As with counseling for any genetic test, in addition, the couple must be advised that if a result is difficult to interpret, further tests and consultation may be required. After they are available, genetic counselors review the laboratory results and may seek clarification as indicated by clinical cytogeneticists or molecular geneticists. Result disclosure requires informing the patient of the implications of the results, recommending any additional testing that is needed to clarify the results, and discussing implications for other family members. Variants of uncertain clinical significance are often reported, along with the possibility of future reclassification. Incidental and secondary findings are reported if the patient did not opt out of receiving these results. Genetic counselors also discuss in generalized terms the implications of the results on future management of the pregnancy and infant after birth. For certain conditions, the availability of fetal therapy can be discussed, along with suggestions for appropriate subspecialist referrals depending on the specific findings. Providers can address options regarding continuation or termination of the pregnancy within the legal limitations of their location of practice while always respecting the personal thoughts of patients on whether this is an acceptable path for them.

For parents at increased risk for a genetic condition in their children, the principal goal and benefit of PGT and prenatal genetic diagnosis is to be able to consider pregnancies that they might otherwise not have considered. PGT offers them a means to avoid pregnancies with an affected fetus, while through prenatal diagnosis they can learn early in a pregnancy if the fetus has the condition, allowing them to make an informed decision about whether to continue the pregnancy. For parents at low or average risk of having a child with a genetic disorder, the great majority of prenatal genetic screens and follow- up diagnostic tests ultimately end in reassurance. The primary objective of prenatal diagnosis is to determine whether the fetus is affected or unaffected with the disorder in question. Irrespective of the reason why testing is pursued, parents should be informed about all available options in the event of an abnormal result. Diagnosis of an affected fetus will allow parents to prepare emotionally and medically for the management of a newborn with a disorder. Termination of pregnancy is one choice they can make, but it is important parents understand that by undertaking prenatal diagnosis there is no implied obligation to terminate a pregnancy in the event of an abnormal result.

In closing, prenatal genetic screening and diagnosis is a rapidly evolving discipline. Standards of care in this field will continue to be modified and refined because of the fast- paced technologic advances in methods available for assessing the fetus and the fetal genome, the ongoing discussions on social and ethical norms, and the varying governmental policies concerning prenatal diagnosis in different cultures and countries around the globe.

اخر الاخبار

اخبار العتبة العباسية المقدسة

الحلقة 24 من جائزة العميد القرآنية تشهد تأهّل القارئ عبد الله محمد من باكستان إلى المرحلة النهائية.

تكريم طلبة جامعة العميد الفائزين في المسابقة الثقافية الكبرى للمطالعة والقراءة

معهد القرآن الكريم النسوي يطلق مسابقته القرآنية (قصة آية) في النجف الأشرف

الجامعة التكنولوجية: برنامج العتبة العباسية المقدسة الرمضاني يعزز القيم الثقافية والإنسانية في الجامعات

المزيد

الآخبار الصحية

دراسة: تناول القهوة يوميا يخفض خطر الإصابة بالاضطرابات النفسية

عرض شائع في الفم قد يكون مرتبطا بخطر الإصابة بأمراض خطيرة

نصائح عامة لاستخدام سماعات الرأس بأمان

تأثير اللياقة البدنية على الدماغ

المزيد

الآخبار التكنلوجية

ديدان الأرض تكشف تلوث التربة بالمعادن الثقيلة

خبير أرصاد جوية: ظاهرة النينيو القادمة قد تكون الأقوى خلال 10 سنوات

"ناسا" تكشف موعد إعادة إطلاق رحلتها المأهولة إلى القمر

علماء الجيولوجيا يفكون لغز الصدع العملاق تحت الماء في المحيط الأطلسي

المزيد

مواضيع ذات صلة

Maternal Inheritance of Disorders Caused by Variants in the Mitochondrial Genome

Genetic Screening in Populations

Fetal Surgical and Medical Interventions

X-Linked Inheritance

Preconception Genetic Screening and Testing

Problems in Prenatal Chromosome Analysis and Gene Sequencing

Introduction to Cytogenetics and Genome Analysis

Methods to Detect Fetal Chromosomal Abnormalities

The Origin and Frequency of Different Types of Mutation

Noninvasive Prenatal Screening by Analysis of Cell- Free Fetal DNA

Screening for Down Syndrome and Other Aneuploidies

Screening for Neural Tube Defects