Risk factors for pre-eclampsia in clinical practice guidelines: Comparison with the evidence

OBJECTIVE

To compare pre-eclampsia risk factors identified by clinical practice guidelines (CPGs) with risk factors from hierarchical evidence review, to guide pre-eclampsia prevention.

DESIGN

Our search strategy provided hierarchical evidence of relationships between risk factors and pre-eclampsia using Medline (Ovid), searched from January 2010 to January 2021.

SETTING

Published studies and CPGs.

POPULATION

Pregnant women.

METHODS

We evaluated the strength of association and quality of evidence (GRADE). CPGs (n = 15) were taken from a previous systematic review.

MAIN OUTCOME MEASURE

Pre-eclampsia.

RESULTS

Of 78 pre-eclampsia risk factors, 13 (16.5%) arise only during pregnancy. Strength of association was usually 'probable' (n = 40, 51.3%) and the quality of evidence was low (n = 35, 44.9%). The 'major' and 'moderate' risk factors proposed by 8/15 CPGs were not well aligned with the evidence; of the ten 'major' risk factors (alone warranting aspirin prophylaxis), associations with pre-eclampsia were definite (n = 4), probable (n = 5) or possible (n = 1), based on moderate (n = 4), low (n = 5) or very low (n = 1) quality evidence. Obesity ('moderate' risk factor) was definitely associated with pre-eclampsia (high-quality evidence). The other ten 'moderate' risk factors had probable (n = 8), possible (n = 1) or no (n = 1) association with pre-eclampsia, based on evidence of moderate (n = 1), low (n = 5) or very low (n = 4) quality. Three risk factors not identified by the CPGs had probable associations (high quality): being overweight; 'prehypertension' at booking; and blood pressure of 130-139/80-89 mmHg in early pregnancy.

CONCLUSIONS

Pre-eclampsia risk factors in CPGs are poorly aligned with evidence, particularly for the strongest risk factor of obesity. There is a lack of distinction between risk factors identifiable in early pregnancy and those arising later. A refresh of the strategies advocated by CPGs is needed.