Dating scan nuchal fold
At this stage, the CRL is defined as the longest dimension of the embryonic pole (Fig. Beginning with the 8th week of gestation, the embryonic head and torso become identifiable.At this point, the CRL is defined as measurement between the top of the fetal head and the fetal rump along its longitudinal axis (Fig. Whereas some investigators advocate using the average of three CRL measurements to establish gestational age, most use the single best measurement. The fetus is in a neutral position and occupies the majority of the image. The accuracy of CRL measurement decreases with gestational age.EARLY FIRST TRIMESTER SCAN (5 TO 10 WEEKS’ GESTATION) The embryonic stage, ending at 10 weeks’ gestation, is a time of very rapid change in the small, developing conceptus.Ultrasound before 11 weeks’ gestation is not typically regarded as a routine part of pregnancy assessment.
During this time frame, the fetus reaches a size and stage of development sufficient to allow for the performance of an informative anatomic survey.
In the 11th week of gestation, the fetus begins to flex and extend its body to a degree that may significantly affect CRL; therefore, CRL measurements need to be carefully standardized from this point on (Fig. Between 7 and 11 WEEKS’ GESTATION) The late first trimester scan is generally considered to be the first scheduled point for routine ultrasound assessment in pregnancy.
It provides the same information as the early first trimester scan with a number of additional benefits.
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.
Although the anatomy of embryo is not typically examined in detail, a variety of severe congenital anomalies (e.g., severe amniotic band syndrome, body-stalk anomalies, and conjoined twins) may be identified even at this point.