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

Abstract

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.