Baby dating scan accuracy
It is common to make at least 2 and often 4 or 5 measurements to estimate gestational age.
In most cases, BPD [Biparietal diameter], HC [Head circumference], AC [Abdominal circumference] and FL [Femur length] are used.
The accuracy rate is very low, many women are pressured into interventions that do more harm than good, and even the mere PREDICTION of macrosomia (large baby) alters the way physicians perceive and treat labor.
A number of studies have questioned the use of ultrasound for estimated fetal birth weight.
The abdominal circumference is measured at the level of the liver and stomach, including the left portal vein at the umbilical region.
If we assume a fetus is growing normally, biometric measurements are determined by gestational age, and we can estimate the gestational age and thus the due date.
The strong acoustic shadow behind the femoral or humeral shaft and the visualisation of both cartilaginous ends indicates that the image plane is on the longest axis and is the optimal measurement plane.
The calipers are placed along the diaphyseal shaft excluding the epiphysis.
Gestational Sac: The first element to be measurable is the gestation sac of the early pregnancy.
It is not expected that BPD be used to assess gestation late in pregnancy.
The values from 33 weeks are intended to predict the growth in fetal head size from a known gestation.
Measurements in the beam axis are more accurate than those made across the axis. Crown-Rump Length (CRL) and femur length) should be measured across the axis.
The earliest measurement of gestational age taken in pregnancy should usually be accepted as the definitive assessment, subsequent examinations reflecting only fetal growth in the intervening period.