Dating scan nuchal fold updating opensim
Serial examinations may be needed to reach a diagnosis.The transvaginal approach should be used in all circumstances where a viable intrauterine pregnancy is not obvious on transabdominal assessment.This chapter deals with normal fetal anatomy; however, frequent references to anomalies are made to underscore the pertinence of a good anatomic evaluation.Each image used in this chapter was obtained using two-dimensional (2D) ultrasound.Three-dimensional (3D) ultrasound can be a useful adjunct to 2D ultrasound in select circumstances and will be discussed in Chapter 2.
At this early stage, the gestational age is being estimated by determination of the mean sac diameter (MSD): the average of the sac length, width, and depth.
Optimal timing of the first trimester scan involves some compromise.
Nuchal translucency assessment is easier to perform and more sensitive at an earlier gestation (11 to 12 weeks), whereas anatomy is best assessed at a slightly later gestation (12 to 13 weeks).
A number of markers, the most important of which is the nuchal translucency measurement, can be employed to provide an accurate risk assessment for aneuploidy.
It should also be stressed that an increased translucency and the presence of other markers, most notably tricuspid valve regurgitation and an abnormal ductus venosus (DV) Doppler waveform, increase the risk of structural abnormalities even in chromosomally normal fetuses.
When performed, the examination is generally limited to determination of the location and number of gestations present, determination of chorionicity in cases of multiple gestations, assessment for viability, and estimation of gestational age.