Maternal factors associated with labor dystocia in low-risk nulliparous women. A systematic review and meta-analysis

Objective: To identify maternal factors associated with labor dystocia in low-risk nulliparous women. Methods: MEDLINE, Embase, ClinicalTrials.gov, Cochrane, and CINAHL were searched for intervention studies and observational studies published from January 2000 to January 2022. Low-risk was defined as nulliparous women with a singleton, cephalic birth in spontaneous labor at term. Labor dystocia was defined by national or international criteria or treatment. Countries were restricted to OECD members. Two authors independently screened 11,374 titles and abstracts, extracted data, and assessed risk of bias using the Newcastle-Ottawa Scale. Results were presented narratively and by meta-analysis when compatible. Results: Seven cohort studies were included. Overall, the certainty of the evidence was moderate. Three studies found that higher maternal age was associated with an increased frequency of labor dystocia (relative risk 1.68; 95% CI 1.43-1.98). Further three studies found that higher maternal BMI was associated with increased fre-quency of labor dystocia (relative risk 1.20; 95% CI 1.01-1.43). Maternal short stature, fear of childbirth, and high caffeine intake were also associated with an increased frequency of labor dystocia, while maternal physical activity was associated with a decreased frequency. Conclusion: Maternal factors associated with an increased frequency of labor dystocia were mainly maternal age, physical characteristics, and fear of childbirth. Maternal physical activity was associated with a decreased fre-quency. Intervention studies targeting these maternal factors would need to be initiated before or early in pregnancy to test the causality of the identified factors and labor dystocia.