Development of a national maternity early warning score: centile based score development and Delphi informed escalation pathways

Abstract

Objective: To derive a new maternity early warning score (MEWS) from prospectively collected data on maternity vital signs and to design clinical response pathways with a Delphi consensus exercise.

Design: Centile based score development and Delphi informed escalation pathways.

Setting: Pregnancy Physiology Pattern Prediction (4P) prospective UK cohort study, 1 August 2012 to 28 December 2016.

Participants: Pregnant people from the 4P study, recruited before 20 weeks' gestation at three UK maternity centres (Oxford, Newcastle, and London). 841, 998, and 889 women provided data in the early antenatal, antenatal, and postnatal periods.

Main outcome measures: Development of a new national MEWS, assigning numerical weights to measurements in the lower and upper extremes of distributions of individual vital signs from the 4P prospective cohort study. Comparison of escalation rates of the new national MEWS with the Scottish and Irish MEWS systems from 18 to 40 weeks' gestation. Delphi consensus exercise to agree clinical responses to raised scores.

Results: A new national MEWS was developed by assigning numerical weights to measurements in the lower and upper extremes (5%, 1%) of distributions of vital signs, except for oxygen saturation where lower centiles (10%, 2%) were used. For the new national MEWS, in a healthy population, 56% of observation sets resulted in a total score of 0 points, 26% a score of 1 point, 12% a score of 2 points, and 18% a score of ≥2 points (escalation of care is triggered at a total score of ≥2 points). Corresponding values for the Irish MEWS were 37%, 25%, 22%, and 38%, respectively; and for the Scottish MEWS, 50%, 18%, 21%, and 32%, respectively. All three MEWS were similar at the beginning of pregnancy, averaging 0.7-0.9 points. The new national MEWS had a lower mean score for the rest of pregnancy, with the mean score broadly constant (0.6-0.8 points). The new national MEWS had an even distribution of healthy population alerts across the antenatal period. In the postnatal period, heart rate threshold values were adjusted to align with postnatal changes. The centile based score derivation approach meant that each vital sign component in the new national MEWS had a similar alert rate. Suggested clinical responses to different MEWS values were agreed by consensus of an independent expert panel.

Conclusions: The centile based MEWS alerted escalation of care evenly across the antenatal period in a healthy population, while reducing alerts in healthy women compared with other MEWS systems. How well the tool predicted adverse outcomes, however, was not assessed and therefore external validation studies in large datasets are needed. Unlike other MEWS systems, the new national MEWS was developed with prospectively collected data on vital signs and used a systematic, expert informed process to design an associated escalation protocol.

Keywords: Critical care; Obstetrics; Pregnancy complications.

Figure 1

Scoring threshold values for new national maternity early warning score (MEWS), Scottish MEWS, and Irish MEWS, for each vital sign. Green areas score 0 points, yellow areas score 1 point, and red areas score 2 points

Figure 2

Distribution of total early warning scores for new national maternity early warning score (MEWS), Scottish MEWS, and Irish MEWS, in all observation sets

Figure 3

Final formatted version of new national maternity early warning score (MEWS): front page

Figure 4

Final formatted version of new national maternity early warning score (MEWS): back page, showing threshold values and triggers. Specialty trainee (ST) 1-2 and 3+ had ≤2 and ≥3 years of obstetric training, respectively. SBAR=situation, background, assessment, and recommendation