Fetal Interventional

Ultrasonography

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This procedure is non-invasive and poses no harm to either the fetus or the mother. It involves the use of high-frequency sound waves to generate visible images based on the echoes produced by various tissues and organs, including the baby in the amniotic cavity. Typically, the developing embryo becomes visible around the 6th week of gestation. For a comprehensive assessment of major internal organs and extremities to detect any potential abnormalities, the optimal time is usually between the 16th and 20th weeks of gestation.

 

While ultrasound examinations are valuable for assessing factors such as fetal size, position, placental location, amniotic fluid levels, and fetal anatomy appearance, it's important to acknowledge their limitations. Some subtle abnormalities may not become apparent until later in pregnancy, or in some cases, they may not be detected at all. An example of this is Down syndrome (trisomy 21), where morphological irregularities are often subtle, such as an increased nuchal translucency (the subcutaneous space between the skin surface and the underlying cervical spine).

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"Triple" or "Quadruple" screen

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Merging maternal serum assays can enhance the accuracy of identifying fetal abnormalities. The conventional evaluation, known as the "triple screen," involves testing for alpha-fetoprotein (MSAFP), beta-HCG, and estriol (uE3). The expanded "quadruple screen" incorporates inhibin-A into the analysis.

 

For diagnosing trisomy 21, the approach can be determined by the timing of the screening. During the first trimester, a comprehensive assessment involving nuchal translucency, PAPP-A, and beta-HCG yields a high diagnostic success rate. In the second trimester, a quadruple screening featuring measurements of AFP, beta-HCG, unconjugated estriol, and inhibin A also proves highly effective. Combining both approaches significantly improves the detection rates for trisomy 21.

 

The trisomy 21 detection rate for the "triple screen" stands at approximately 70%, with a false positive rate of 7%. In contrast, the "quad screen" achieves an 80% detection rate with a 6% false positive rate. When combining the "quad screen" from the second trimester with the results of PAPP-A and NT measurements from the first trimester, the detection rate for Down syndrome reaches 90%, with a false positive rate of 3%. Without the NT test, using all five serum tests still yields a trisomy 21 detection rate of 87%, with a 3.2% false positive rate.