Maternal early warning scores shown to be methodologically weak and at high risk of bias.

Objective: To systematically review and critically appraise the methodology of developing Modified Obstetric Early Warning Scores (MOEWSs).

Study design and setting: We searched Medline, CINAHL, EMBASE and the Web of Science for MOEWS studies published between 01 January 2000 and 31 December 2023. Eligible studies included models predicting maternal death, ICU admission, and/or a composite of two or more maternal morbidities occurring in a hospital setting in women of any gestational age and up to one week after the end of pregnancy. Models were critically appraised using the Prediction Model Risk of Bias Assessment Tool (PROBAST) and adherence to the Transparent Reporting of Prediction Models (TRIPOD).

Results: 20 studies were included: five (25%) were model development studies, five (25%) were model development and validation, and ten (50%) were validation only. Four development studies used statistical methods, and the remaining six studies used clinical consensus (i.e., expert opinion). The four data-driven model development studies did not address key statistical challenges such as repeated measures or missing data, assess the performance adequately or dataset characterises clearly. All but one study (95%) were rated at high risk of bias due to data sources, poor reporting and analysis limitations. The fifteen validation studies were poorly reported and eleven (73%) were at high risk of bias. None of the data-driven models were independently validated, a key step towards implementation.

Conclusions: There is a lack of MOEWS developed using methods that followed recommended statistical guidelines. Substantial problems with the methodological quality of included studies both in development and validation, along with high risk of bias indicating published scores could perform poorly or be potentially harmful if used in clinical practice. Future work should address handling missing data and repeated measures and consider how a MOEWS will perform in different populations and key subgroups.