11-13 week antenatal scan
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11-13 week antenatal (nuchal translucency) scan is considered a routine investigation advised for fetal well-being as well as for early screening in pregnancy (see antenatal screening).
It includes multiple components and is highly dependent on the operator. Traditionally three factors are used to calculate the risk of trisomies:
must be 45 to 84 mm
gestation age 11 weeks 3 days to 13 weeks 6 days
Additional markers increase the detection rate and reduce false-positive rates:
Combining these factors with blood tests (i.e. dual marker) has been reported to achieve a nearly 95% detection rate for trisomies.
Apart from the screening protocol, early detection of major anomalies may be possible, and the checklist must include the following conditions:
open spina bifida
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- 2. Kenkhuis M, Bakker M, Bardi F et al. Effectiveness of 12-13-week scan for early diagnosis of fetal congenital anomalies in the cell-free DNA era. Ultrasound Obstet Gynecol. 2018;51(4):463-469. doi:10.1002/uog.17487