Calculate a Bishop score from cervical dilation, effacement, station, consistency, and position to gauge cervical favorability for a labor induction.
Bishop Score Formula
The Bishop score is a sum, not a product. You give each of five cervical exam findings a point value and add them together:
Bishop Score = Dilation + Effacement + Station + Consistency + Position
The modified score keeps the same five findings and then adjusts the total for clinical factors:
Modified Score = Bishop Score + Parity + Preeclampsia - Postdates - Nulliparity - PROM
The simplified score uses only the three findings that best predict a vaginal birth:
Simplified Score = Dilation + Effacement + Station
Variables:
- Dilation is how open the cervix is in centimeters, scored 0 (closed), 1 (1 to 2 cm), 2 (3 to 4 cm), or 3 (5 cm or more)
- Effacement is how thin the cervix is as a percentage, scored 0 (0 to 30 percent), 1 (40 to 50 percent), 2 (60 to 70 percent), or 3 (80 percent or more)
- Station is how low the baby sits relative to the ischial spines, scored 0 (-3), 1 (-2), 2 (-1 or 0), or 3 (+1 or +2)
- Consistency is how soft the cervix feels, scored 0 (firm), 1 (medium), or 2 (soft)
- Position is where the cervix points, scored 0 (posterior), 1 (mid), or 2 (anterior)
The standard score ranges from 0 to 13. Pick the scoring method at the top of the calculator. Standard adds the five findings. Modified starts from that total and adds 1 point for preeclampsia and 1 point for each prior vaginal delivery, then subtracts 1 point each for a postdates pregnancy, a first pregnancy (nulliparity), and premature or prolonged rupture of membranes. Simplified drops consistency and position and scores only dilation, effacement, and station on a 0 to 9 scale.
Bishop Score Chart and What the Result Means
Use this chart to turn each exam finding into points. It is the same table the calculator applies behind the scenes.
| Finding | 0 points | 1 point | 2 points | 3 points |
|---|---|---|---|---|
| Dilation (cm) | Closed | 1 to 2 | 3 to 4 | 5 or more |
| Effacement (%) | 0 to 30 | 40 to 50 | 60 to 70 | 80 or more |
| Station | -3 | -2 | -1 or 0 | +1 or +2 |
| Consistency | Firm | Medium | Soft | – |
| Position | Posterior | Mid | Anterior | – |
The next table shows how the total is read, along with the equivalent simplified score. The simplified column comes from the Laughon study, which found that a simplified score above 5 predicted a vaginal delivery about as well as a standard score above 8. Most Bishop calculators stop at the total, so this mapping is a quick way to cross-check a three-finding exam against the full score.
| Standard score | Simplified equivalent | Cervix | What it usually means |
|---|---|---|---|
| 0 to 6 | 0 to 4 | Unfavorable (unripe) | A ripening agent or mechanical method is usually used before or with induction. Higher chance of a long induction. |
| 7 | 5 | Borderline | Ripening is often still considered, especially for a first birth. |
| 8 to 13 | 6 to 9 | Favorable (ripe) | Induction success is close to that of spontaneous labor. Oxytocin alone is often enough. |
Example Problems
Example 1: Standard score.
A cervix is 3 to 4 cm dilated (2), 60 to 70 percent effaced (2), at station -1 (2), soft (2), and anterior (2). Add the points: 2 + 2 + 2 + 2 + 2 = 10. A score of 10 is favorable, so an induction would be expected to work about as well as spontaneous labor.
Example 2: Simplified score.
Using only three findings, a cervix is 5 cm dilated (3), 80 percent effaced (3), and at station 0 (2). The simplified total is 3 + 3 + 2 = 8 out of 9, which sits in the favorable range and matches the standard reading from Example 1.
Frequently Asked Questions
What is a good Bishop score for induction?
A score of 8 or higher is considered favorable. At that level the cervix is ripe and an induction has a success rate close to natural labor. A score of 6 or lower is unfavorable, which usually means a cervical ripening step is recommended first. A score of 7 is borderline and is judged case by case, with a first pregnancy often nudging the decision toward ripening.
What is the difference between the Bishop score and the modified Bishop score?
The core five findings are identical. The modified score then adjusts the total for clinical context: it adds a point for preeclampsia and a point for each previous vaginal delivery, and it subtracts a point each for a postdates pregnancy, a first pregnancy, and premature or prolonged rupture of membranes. Those adjustments can move a borderline total into a clearer favorable or unfavorable range, which is why the calculator offers the modified mode.
What is the simplified Bishop score?
The simplified score uses only dilation, effacement, and station, giving a range of 0 to 9. Researchers found that dropping consistency and position lost almost no predictive power: a simplified score above 5 predicted vaginal delivery with a positive predictive value of about 87.7 percent, compared with 87.0 percent for a standard score above 8. It is a faster way to read cervical readiness when position and consistency are hard to judge.