(GA = gestational age in weeks, calculated from last menstrual period; BPD = biparietal diameter
, FL = femur length, HC = head circumference and AC = abdominal circumference; all measurements in mm):
 Kieler  also compared the expected date of delivery derived from biparietal diameter
and the last regular menstrual period and found that 91.8% delivered within +14 days and 61.8% within seven days of expected date of delivery (EDD) derived using the bi-parietal diameter.
is the most discussed and documented obstetric measurement in the second trimester.
We obtained similar results when we estimated gestational age using biparietal diameter
measurements (not shown).
Table 1 The relationship between sono-graphic fetal biparietal diameter
and gestational age Biparietal Weeks of diameter gestation (*) 4.7 20 5.0 21 5.4 22 5.7 23 6.0 24 6.3 25 6.6 26 (*)Gestational age is estimated in terms of the number of weeks since the first day of the last normal menstrual period, for a fetus of average size (see reference 19).
One hundred fifty-nine patients carrying a single fetus between 11 and 42 weeks' gestational age were selected to participate. Measurements for determining fetal age included biparietal diameter
, head circumference, abdominal circumference, and femur length.
Many parameters are being used for establishing gestational age, for example, biparietal diameter
, head circumference and abdominal circumference.
Fetal growth indices, including biparietal diameter
(BPD), head circumference (HC), abdominal circumference (AC), and femur length, were also measured by ultrasound.
We used the essential parameters for the following measurements: increase of fetal biparietal diameter
(BPD), increase of fetal femur length (FL), increase of estimated fetal body weight (EFBW), fetal biophysical profile (BPP), amniotic fluid index (AFI), and umbilical artery systole/diastole (S/D) ratio.
Fetal biometric measurements include biparietal diameter
, head circumference, abdominal circumference and femur length.
Other factors that independently predicted a statistically significant 4%-17% increased risk for shoulder dystocia at term included estimated fetal weight, femur length, abdominal circumference, and the ratio of femur length to biparietal diameter
, reported Dr.
Fetal biparietal diameter
measurement and fetal renal length show a linear relationship with each other during 2nd and 3rd trimester of pregnancy.2 There is also linear increase in renal length with gestational age.3,4