The Bishop Score is a standardized numerical system used in obstetrics to predict the likelihood of a successful labor induction. Developed by Dr. Edward Bishop in 1964, this scoring system evaluates the physical condition of the pregnant person’s cervix to determine its readiness for labor. The score provides healthcare providers with an objective measure to guide the decision-making process when considering induction. By assessing the cervical status and the baby’s position, the Bishop Score estimates how responsive the body will be to induction methods.
The Five Criteria Used for Measurement
The Bishop Score calculation involves a manual vaginal examination assessing five distinct physical characteristics of the cervix and the fetus. Each characteristic is assigned a point value, ranging from zero to three, with a higher score indicating a cervix more favorable for induction. The combined total of these five factors determines the overall score, which ranges from zero to 13.
Cervical dilation measures how open the cervical opening is in centimeters. A closed cervix receives zero points, while one dilated four centimeters or more is awarded the maximum three points. Cervical effacement describes the thinning and shortening of the cervix, typically measured as a percentage. A cervix less than 30% effaced scores zero points, but one 80% or more effaced receives three points, reflecting the necessary thinning that occurs before active labor.
The third characteristic assessed is the fetal station, which refers to the baby’s head position relative to the mother’s pelvis. This measurement uses the ischial spines, bony prominences within the pelvis, as a zero reference point. A higher position, represented by a negative number like -3, scores zero points. A position at +1 or +2, meaning the head has descended past the spines, earns two points.
Cervical consistency, or firmness, is the fourth factor. A soft cervix, considered ready for labor, is awarded two points, while a firm cervix receives zero points. The final criterion is cervical position, which notes the angle of the cervix relative to the vagina. A cervix pointing backward (posterior) scores zero points, but a cervix positioned forward (anterior) is more favorable and receives two points.
Scoring and What the Numerical Results Predict
The cumulative score provides a prediction tool concerning the potential outcome of a labor induction. The total score (zero to 13) is interpreted to categorize the cervix as unfavorable, borderline, or favorable for induction. This numerical result helps estimate the probability of achieving a vaginal delivery without complications.
A low Bishop Score, generally five or less, indicates an unfavorable cervix not yet ready for labor. This low score suggests that induction is less likely to result in a successful vaginal delivery and may require prolonged methods. A score in this range signals that the cervix is still thick, closed, and positioned toward the back, meaning necessary pre-labor changes have not occurred.
A moderate or borderline score, typically between six and seven, represents an intermediate state of cervical readiness. While this range is not a guarantee of rapid success, it suggests the cervix has begun preparatory changes for labor. Clinical judgment is important with these moderate scores, as induction may succeed but could still be lengthy.
A high Bishop Score, defined as eight or greater, is predictive of a favorable cervix and a high probability of a successful vaginal birth. A score in this upper range indicates the cervix is already soft, significantly thinned and dilated, and the baby’s head is well-positioned. When the score is eight or above, the likelihood of a successful induction approaches that of spontaneous labor.
Guiding Clinical Decisions for Labor Induction
The predictive power of the Bishop Score translates directly into clinical decisions regarding labor induction strategy. A provider uses the score to tailor the induction approach to the individual’s readiness, aiming to optimize the chances of a successful vaginal delivery. The score helps determine whether the cervix first needs to be “ripened” or can proceed directly to stimulating contractions.
When a patient presents with a low Bishop Score of five or less, the clinical decision involves initiating cervical ripening before attempting to stimulate contractions. Ripening agents, such as prostaglandin medications (dinoprostone or misoprostol), are administered to soften and thin the cervix. Mechanical methods, like inserting a balloon catheter, may also be used to encourage dilation.
If the Bishop Score is high (typically eight or more), the cervix is prepared enough to bypass the initial ripening phase. The healthcare provider may proceed directly to methods designed to start contractions, such as administering oxytocin intravenously. Alternatively, the provider might rupture the membranes (break the water) to stimulate the onset of labor.
The Bishop Score is a tool used to choose the right starting point for induction, making the process more efficient and safer for both the patient and the baby. It helps prevent unnecessary delays or the use of contraction-stimulating drugs on an unprepared cervix, which could increase the risk of a failed induction or cesarean delivery. By guiding the choice of intervention, the score helps personalize the induction plan.