Screening

Antenatal screening for fetal chromosomal conditions

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women, regardless of maternal age, be offered antenatal screening and invasive diagnostic testing for aneuploidy.[36] Importantly, the ACOG guidelines encourage pre-test and post-test counselling. Women should be counselled regarding the differences between screening and invasive diagnostic testing. The UK National Screening Committee also recommends antenatal screening for DS, Edwards' syndrome and Patau's syndrome.[37]

First-trimester screening, a combination of nuchal translucency measurement, serum markers (pregnancy-associated plasma protein A and free or total beta-human chorionic gonadotropin [hCG]), and maternal age, is 79% to 90% sensitive in detecting DS.[38][39][40][41][42]​ If a woman is discovered to be at an increased risk of fetal aneuploidy, then genetic counselling and chorionic villus sampling (CVS) is offered, or she may choose to have a second-trimester amniocentesis (invasive diagnostic testing).[36]

The integrated screening approach uses both the first and second-trimester markers to adjust a woman's age-related risk of having a child with DS. The integrated approach is more sensitive, with lower false-positive rates than first-trimester screening alone. It provides a detection rate of 94% to 96%.[43]

A second method is the sequential screening approach, in which the patient is informed of the first-trimester screening results, then is given the option to receive further diagnostic testing in the second trimester.

First-trimester ultrasonographic markers, such as a non-visualised nasal bone, tricuspid regurgitation, crown-rump length, femur and humeral length, head and trunk volumes, and umbilical cord diameters, need further investigation regarding utility for screening protocols. Second-trimester ultrasonographic markers such as echogenic bowel, intracardiac echogenic focus, and dilated renal pelvis have a low sensitivity and specificity for DS.[44]

Additionally, in North America and the UK, non-invasive prenatal (antenatal) screening (NIPS) is recommended as part of the antenatal care screen in high-risk patients for fetal aneuploidy.​[37][45]​​​ The clinical use of NIPS has become increasingly common as it provides women with a more sensitive non-invasive screening option, with positive predictive values around 80% and negative predictive values reported to be as high as 99% to 100% in higher prevalence populations such as those with advanced maternal age.[46][47]​​ Other clinical non-invasive screening modalities for DS include: the first-trimester screen, with a detection rate of 75% to 80%; and the maternal serum screen, with a detection rate of 80%. NIPS evaluates cell-free DNA that circulates in maternal blood, and can be done as early as 9 weeks' gestation. While numerous studies have shown NIPS to be both highly sensitive and highly specific, conclusive confirmation of NIPS screening results can only be done via amniocentesis and CVS.[46][48]​​ Physicians should discuss the risks, benefits, and limitations of antenatal screening and diagnostic testing with patients.[48][49]​​​

Postnatal screening

Asymptomatic children are not screened for DS postnatally.

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