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 distance from the top of the pubic bone (symphysis pubis) to the top of the pregnant uterus (fundus) is measured in centimeters (cm).
The SFH in centimeters should be equal to the gestational age in weeks.
Many regression equations are available using various combinations of parameters to estimate the gestational age.
Some clinicians use the unweighted mean of the 4 most commonly used biometric parameters ( biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) ) to establish a gestational age  Ultrasound Estimate of Fetal Weight In practice the most common equations for calculating the estimated fetal weight (EFW) are reported to be the Shepard and Hadlock formulas [5,8,9]: Shepard: Log 10 (weight) = -1.7492 0.166*BPD 0.046*AC - 2.646*(AC*BPD)/1,000 Hadlock 1: Log 10 (weight) = 1.304 0.05281*Ac 0.1938*FL -0.004*AC*FL Hadlock 2: Log 10 (weight) = 1.335-0.0034*AC*FL 0.0316*BPD 0.0457*AC 0.1623*FL Hadlock 3: Log 10 (weight) =1.326-0.00326 *AC*FL 0.0107*HC 0.0438*AC 0.158*FL Hadlock 4: Log10 (weight) =1.3596 -0.00386* AC * FL 0.0064*HC 0.00061*BPD*AC 0.0424*AC 0.174*FL Regardless of the formula used the accuracy of the sonographic estimate of the EFW is affected by supoptimal imaging and biological variation . al., Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters.
TABLE 2 70% of infants born below the 10th percentile are not at risk for adverse outcomes .
The sensitivity of SFH measurement for detecting abnormal intrauterine growth was less than 35% in one study . found that the sensitivity of SFH measurement for detecting fetal growth abnormalities could be improved by serial plotting of the SFH on customized charts . Hadlock FP, et al., In utero analysis of fetal growth: a sonographic weight standard. Large for gestational age (LGA) is generally used to describe a birth weight equal to or greater than the 90th percentile for a given gestational age . However, there is not universal agreement on these definitions , and some have proposed the 15th and 97th percentiles as more optimal cut-offs to define SGA and LGA respectively . 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. Monochorionic twins growth rate growth begins to slow at 28 weeks and averages about 170 grams per week thereafter until 37 weeks  After obtaining a reliable gestational age and best estimate of the fetal weight, a growth chart or weight table may be used to assign an EFW growth percentile .