What is a Bishop’s Score and How Does it Relate to Inducing Labor?
A Bishop’s Score refers to a group of measurements used to determine whether a woman may have a successful vaginal delivery and whether labor ought to be induced. Bishop’s Score is based on station, dilation, effacement, position and consistency.
Station is a term used to describe the descent of the baby into the pelvis. An imaginary line is drawn between the two bones in the pelvis (known as ischial spines). This is the "zero" line, and when the baby reaches this line it is considered to be in "zero station." When the baby is above this imaginary line it is in a minus station. When the baby is below, it is in a "plus" station. Stations are measured from -5 at the pelvic inlet to +4 at the pelvic outlet.
Dilation is measured in centimeters, from 0 to 10. Your cervix is fully open and you should be able to push when it is dilated to 10 centimeters. Occasionally, a physician will measure dilation in "fingers." Dilation often begins days or weeks before labor actually begins. At first, the progress may be very slow. Some women may be dilated 2 to 3 centimeters long before labor. Once active labor begins, you will begin to dilate more quickly.
Effacement refers to the softening and thinning of the cervix. You won’t feel this happening; it may only be measure with a vaginal exam. Effacement is measured in percent. When your cervix is normal, it is considered to be 0% effaced. When you’re 50% effaced, your cervix is half its original thickness. When your cervix is 100% effaced it is completely thinned out and you are ready for vaginal delivery.
Position refers to the positioning of the cervix. If the cervix faces front (anterior) it is more favorable, while posterior is less favorable.
Consistency of the cervix is measured on a scale of firmness from firm to soft. The softer the cervix is, the better the chance of vaginal delivery.
The Bishops Score generally follows this scale:
Score Dilatation Effacement Station Position Consistency
0 closed 0 – 30% -3 posterior firm
1 1-2 cm 40 -50% -2 mid-position moderately firm
2 3-4 cm 60 -70% -1,0 anterior soft
3 5+ cm 80+% +1,+2
A point is added to the score for each of the following:
Each prior vaginal delivery
A point is subtracted from the score for:
Premature or prolonged rupture of membranes
cesarean rates: first time mothers women with past vaginal deliveries
scores of 0 – 3: 45% 7.7%
scores of 4 – 6: 10% 3.9%
scores of 7 – 10: 1.4% .9%
Induction is generally attempted when a mother has a favorable Bishop’s score. A mother may be given misoprostol, cytotec or prostaglandin gel to help ripen the cervix and improve the score. A score of five or less is said to be "unfavorable." If induction is indicated, the mother would be a candidate for a cervical ripening agent. These are usually introduced one or two nights before the planned induction. A score of eight or nine would indicate that the cervix was very ripe and induction would have a high probability of being successful.
Your physician can assist you in understanding and interpreting your own Bishop’s Score.