Modified Bishop score vs the original Bishop score

What is the modified Bishop score?

The modified Bishop score is a version of Edward Bishop's 1964 pelvic score in which the length of the cervical canal, in centimetres, replaces effacement, recorded as a percentage. The change is usually credited to Calder and colleagues, who used "a modified Bishop scoring system" to rate the inducibility of 40 women at 38 to 42 weeks in the Journal of Obstetrics and Gynaecology of the British Commonwealth in 1974. The full 2008 NICE guideline on induction of labour printed the modified table next to Bishop's original in its Appendix B and advised assessing the cervix "using the Bishop score or a modification of this". In that table, dilation, cervical length and station score 0 to 3 points each, consistency scores 0 to 2, and position scores 0 or 1, so the total runs from 0 to 12 rather than 0 to 13. The current NICE guideline, NG207, defines the Bishop score by "effacement (or length)".

Modified vs original Bishop score, item by item

The modified and original Bishop scores share three items unchanged, change one, and replace one. Station keeps the same four bands in both, from −3 for 0 points to +1 or +2 for 3 points, and consistency keeps three grades from firm to soft, with "medium" in Bishop's table called "average" in the modified one. Dilation keeps four bands but moves the cut points: the original gives 0 for a closed cervix, then 1–2, 3–4 and 5–6 cm, while the modified table gives 0 below 1 cm, then 1–2, 2–4 and over 4 cm. Cervical length replaces effacement, scoring 0 for over 4 cm, 1 for 2–4 cm, 2 for 1–2 cm and 3 for under 1 cm. Position is where the maximum changes: Bishop gives 0, 1 or 2 for posterior, mid or anterior, while the modified table gives 0 for posterior and 1 for mid or anterior. That single point is why the modified total stops at 12.

Original table from Bishop (1964) as reprinted by ACOG in 2025, total 0–13; modified table from the 2008 NICE guideline, Appendix B, Table B.2, total 0–12.

Which cut-offs apply to the modified Bishop score?

The modified Bishop score has no cut-off of its own in current guidelines; the published thresholds are written for "the Bishop score", and NICE defines that score in a way that covers both versions. In Calder's 1974 study, inducibility scores of 2 to 5 were treated as unfavourable and 6 to 8 as favourable. NICE NG207 (2021) defines the Bishop score as based on dilation, "effacement (or length)", position, consistency and station, says 8 or more generally indicates a cervix ready to dilate, and uses 6 or less versus more than 6 to help choose between groups of induction methods. ACOG Clinical Practice Guideline No. 9 (2025) reprints Bishop's original table, says there is no universally accepted definition of an unfavourable cervix, and notes that studies have used cut-offs from 3 to 8. Because the modified table tops out one point lower and scores an anterior cervix as 1, a cervix can fall on the other side of a cut-off depending on the table used.

Worked example: one cervix, two scores

One examination scored with both tables shows how the two versions of the Bishop score can disagree. A woman at term has a cervix that is 1 cm dilated, about 50% effaced and 2.5 cm long, with the head at station −1, a medium (average) consistency and an anterior position. On Bishop's original table she scores 1 for dilation, 1 for effacement of 40–50%, 2 for station, 1 for consistency and 2 for an anterior cervix, a total of 7. On the modified table she scores 1 for dilation of 1–2 cm, 1 for a length of 2–4 cm, 2 for station, 1 for average consistency and 1 for a mid or anterior cervix, a total of 6. The original score is above the NICE split of 6, while the modified score sits in the 6-or-less group. Had her cervix been mid-position, both tables would give 6. Enter her findings in the Bishop score calculator to check the original score.

Other scores called modified or simplified Bishop

The name "modified Bishop score" does not always point to the same table, so check which one a study, protocol or calculator used. The version in the 2008 NICE guideline, with cervical length bands of over 4, 2–4, 1–2 and under 1 cm and a maximum of 12, is the one most often credited to Calder. Some later studies describe a modified Bishop score that runs from 0 to 13, for example a 2024 study of 100 women in Patna, India, in the Journal of Family Medicine and Primary Care, and some online calculators add or subtract points for clinical factors such as parity. A separate idea is the simplified Bishop score of Laughon and colleagues (2011). In 5,610 nulliparous women, only dilation, station and effacement were significantly linked to vaginal birth, so the simplified score keeps those three items and runs from 0 to 9. A simplified score above 5 had a positive predictive value of 87.7%, against 87.0% for the original score above 8.

When you report a score, name the version and the maximum, for example "modified Bishop 6/12" or "Bishop 7/13". The Bishop score calculator on this site uses Bishop's original 0–13 table, the one ACOG reprints.