BACKGROUND While Doppler ultrasound screening is beneficial for women with high-risk pregnancies, there is insufficient evidence on its benefits and harms in low- and unselected-risk pregnancies . This may be related to fewer events of abnormal Doppler flow, however the prevalence of absent or reversed end diastolic flow (AEDF or REDF) in such women is unknown . In this systematic review, we aimed to synthesise available data on the prevalence of AEDF or REDF .
METHODS We searched PubMed, Embase, CINAHL, CENTRAL and Global Index Medicus with no date, setting or language restrictions . All randomized or non-randomized studies reporting AEDF or REDF prevalence based on Doppler assessment of umbilical arterial flow> 20 weeks' gestation were eligible . Two authors assessed eligibility and extracted data on primary (AEDF and REDF) and secondary (fetal, perinatal, and neonatal mortality, caesarean section) outcomes, with results presented descriptively .
RESULTS A total of 42 studies (18,282 women) were included . Thirty-six studies reported zero AEDF or REDF cases . However , 55 AEDF or REDF cases were identified from just six studies (prevalence 0.08% to 2.13 %). Four of these studies were in unselected-risk women and five were conducted in high-income countries . There was limited evidence from low- and middle-income countries .
CONCLUSIONS Evidence from largely observational studies in higher-income countries suggests that AEDF and REDF are rare among low- and unselected-risk pregnant women. There are insufficient data from lower-income countries and further research is required.