Ultrasound screening in the first trimester of pregnancy
Keywords:
Ultrasound screening, prenatal ultrasound, birth defects, fetal nuchal translucency thickness, trisomy 21Abstract
Fetal nuchal translucency thickness (NT) at 11–13+6 weeks scan has been combined with maternal age to provide an effective method of screening for trisomy 21; for an invasive testing rate of 5%, about 75% of trisomic pregnancies can be identified. When maternal serum free ß-human chorionic gonadotropin (ß-hCG) and pregnancy-associated plasma protein-A (PAPP-A) at 11–13+6 weeks are also taken into account, the detection rate of chromosomal defects is about 85–90%.It was found that in 60–70% of
fetuses with trisomy 21, the nasal bone is not visible in the 11–13+6 weeks scan and examination of the nasal bone can increase screening detection rate by the first trimester scan and serum biochemistry to more than 95%. In addition to its role in the assessment of risk for trisomy 21, increased nuchal translucency thickness can also identify a high proportion of other chromosomal defects and is associated with major abnormalities of the heart and great arteries, and a wide range of genetic syndromes.
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