Aneuploidy Screening During Pregnancy
About 3% to 5% of nowadays pregnancies are complicated by birth defects or genetic disorders. Chromosomal abnormalities appear in about 1 out of 150 live births, and congenital anomalies remain the main cause of infant death and the main cause of childhood death. Aforesaid chromosomal abnormalities include aneuploidy (defined as the presence of one or more missing or extra chromosomes), translocation, duplication, and deletion.
Whilst trisomy 21 (or Down syndrome) is the most common chromosomal disorder appear in about 1 out of 800 live births, trisomy 13 and 18 can also lead to live births with a significantly lower frequency. Less common than autosomal aneuploidies are Sex chromosome aneuploidies. Monosomy X (or Turner syndrome) is the only known viable monosomy.
The age of mother increases the risk of aneuploidy. Other factors also influence the patient’s risk for any given pregnancy. Among them are the presence of soft markers or birth defects on an ultrasound scan and past obstetric history, especially if this is characteristic of a previous pregnancy caused by aneuploidy, or another genetic disorder. The current risk of aneuploidy during pregnancy increases a past family history of aneuploidy increases, especially if the parent is a balanced carrier of Robertson translocations, although most cases are sporadic and secondary to chromosomal nondisjunction.
Patients report many different motives for aneuploidy screening or prenatal diagnosis. Some may choose to terminate their pregnancy if the defect is detected early enough. Others may do screening or testing so that they have time to process the diagnosis and look for experienced clinicians who can help them prepare to care for a sick child and look after their child after giving birth. Some birth defects, such as some neural tube defects, may be eligible for prenatal treatment, with subsequent improvement in neonatal outcomes. All patients who decide to be screened or tested should be consulted about the risks, benefits, and limitations of their chosen test plan from their healthcare provider or genetic counselor. It is important to note that screening and testing decisions for aneuploidy are largely determined by value. A frank discussion of the benefits, risks and limitations of testing is key to ensuring that the appropriative care is tailored to each patient’s individual goals.
In 2007, the American Congress of Obstetrician-Gynecologists (ACOG) has recommended that the proper aneuploidy screening or invasive testing should be available to all women, ideally on their first prenatal visit. This idea was revolutionary at the time, because previously only the women who were considered at high risk were offered these tests. It is important to note that currently, cell-free DNA for aneuploidy screening, is recommended by ACOG only to women at high risk of aneuploidy before testing.
With maximum certainty, diagnostic testing allows patients to know, whether their pregnancy may be affected by a specific genetic condition or not. At present, the most common indication for diagnostic testing in Ukraine is mother’s age of 36 years or older at the estimated date of delivery. Other common symptoms include positive aneuploidy screening results, a known family history of genetic disorders or abnormalities detected by ultrasound. Whilst diagnostic testing is recommended by ACOG to be accessible to all women, regardless of mother’s age, patients should be consulted before proceeding on a risk of pregnancy loss.
Aneuploidy screening or diagnostic testing during pregnancy should be offered to all women. Equally important, the available options should be explained in detail to patients and their families, in particular, including the benefits and risks of each option, and how the results can be presented. Cell-free embryonic DNA technology remains aneuploidy screening test so patients should be advised that due to the low prevalence of these disorders this test and that microdeletion testing continues to give poor positive predictive values. To undergo more than one screening method is not recommended, and women with positive screening and those who wish to undergo further testing are advised to consult a diagnostic test with amniocentesis as not to delay the diagnosis. Amniocentesis is becoming safer with lower rates of pregnancy loss and should remain accessible to all women who want to do diagnostic testing, regardless of the presence or absence of abnormalities or risk factors.
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