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Table 1 Characteristics of included studies

From: Prevalence of abnormal umbilical arterial flow on Doppler ultrasound in low-risk and unselected pregnant women: a systematic review

Study design N %
Case–control study 7 16.7
Cross-sectional study 12 26.2
Cohort study 19 45.2
Randomized controlled trial 4 9.5
Country income level   
 High-income countries 24 57.1
 Upper-middle income countries 13 31.0
 Low-middle income countries 4 9.5
 Low-income countries 0 0.0
 Multiplea 1 2.1
  1. aOne study was a multi-country study conducted in Brazil (upper-middle income country), Kenya (low-middle income country) and the UK (high-income country)