Morgan, Thurnau et al developed the fetal-pelvic index to identify fetal-pelvic disproportion in a pregnant woman. This can help determine if it is safe to attempt vaginal delivery after a previous cesarean section. The authors are from the University of Oklahoma.
Parameters:
(1) fetal abdomen transverse diameter in cm
(2) fetal abdomen anteroposterior diameter in cm
(3) fetal head transverse diameter in cm
(4) fetal head anterioposterior diameter in cm
(5) maternal pelvic inlet transverse diameter in cm
(6) maternal pelvic inlet anteroposterior diameter in cm
(7) maternal midpelvis transverse diameter in cm
(8) maternal midpelvis anterioposterior diameter in cm
circumference of fetal abdomen in cm =
= (0.5 * PI() * ((transverse diameter) + (AP diameter))
circumference of fetal head in cm =
= (0.5 * PI() * ((transverse diameter) + (AP diameter))
circumference of maternal pelvic inlet in cm =
= (0.5 * PI() * ((transverse diameter) + (AP diameter))
circumference of maternal midpelvis in cm =
= (0.5 * PI() * ((transverse diameter) + (AP diameter))
difference 1 =
= (fetal head circumference) - (maternal midpelvis circumference)
difference 2 =
= (fetal head circumference - (maternal pelvic inlet circumference)
difference 3 =
= (fetal abdominal circumference) - (maternal midpelvis circumference)
difference 4 =
= (fetal abdominal circumference - (maternal pelvic inlet circumference)
fetal-pelvic index =
= SUM(2 most positive of the 4 differences)
Interpretation:
• A fetal-pelvic index > 0 indicates fetal-pelvic disproportion is present.
• A fetal-pelvic index < 0 indicates that fetal-pelvic disproportion is absent.
