Knowing The Estimated Fetal Weight?
why is the TBJ formula one minus 12/11 and multiplied by 155???
Hello Jumria Ingo, thanks for the question for HealthReplies.com
The formula you mean is probably Johnson's formula to find the estimated fetal weight (BJ) from the height of the uterine fundus (TFU). The correct formula is as follows:
BJ (in grams) = (TFU (in cm) - n) x 155
n = 11 if the baby's head has not entered the pelvic inlet (PAP)
n = 12 if the baby's head has entered the PAP
These fixed numbers (115, 11, 12) are constants that were already defined when the formula was created.
Since ultrasound has been widely used, this formula has been abandoned because it is considered inaccurate in determining fetal weight. This inaccuracy is due to the fact that the TFU measurement is determined by many things, including the thickness of the mother's belly fat, the mother's position or the baby's position during measurement, and others.
That's all the information from me, I hope it's enough to answer
dr. Irna Cecilia