Dating ultrasound measurements
TABLE 2 70% of infants born below the 10th percentile are not at risk for adverse outcomes .
The difference in size between babies is most often due to constitutional causes such as the size of the baby's parents, ethnic background , or the sex of the baby .
It is recommended that crown-rump length be used up to 84 mm, and other parameters be used for measurements 84 mm the biparietal diameter (BPD) or head circumference (HC) is the best predictor of gestational age  . et al., Sonographic estimation of fetal age and weight.
However, using multiple parameters is superior to using a single parameter to establish a gestational age in the second trimester . Shepard MJ, Richards VA, Berkowitz RL, et al: An evaluationof two equations for predicting fetal weight by ultrasound.
The SFH in centimeters should be equal to the gestational age in weeks.
ACOG advises newborns whose birth weight is less than the 10th percentile for gestational age are considered small for gestational age (SGA) .
Whereas a fetus with a weight that is less than the 10th percentile for its gestational age is considered to have fetal growth restriction (FGR), also known as intrauterine growth restriction (IUGR) [5, 7].
The SFH is measured using a tape placed over the mother's abdomen.
The mother's bladder should be empty when the measurement is done.
Many regression equations are available using various combinations of parameters to estimate the gestational age.