Although the assessment of the amniotic fluid volume in pregnancy is part of the fetal wellbeing surveillance, the impact of idiopathic polyhydramnios (IP) on maternal and perinatal outcomes in unknown. The aim of this meta-analysis was to investigate the association of IP with different maternal and perinatal outcomes. We screened five electronic databases until December 2023 and performed data extraction and quality assessment using ROBINS-E in duplicates. Pooled risk ratios and 95% confidence intervals (95% CI) were calculated with a random effects model. 38 studies were included. Patients with IP were at increased risk of perinatal complications including preterm delivery (RR 1.96, 95% CI 1.35–2.86; I2 = 92%), placental abruption (RR 3.20, 95% CI 2.20–4.65; I2 = 2%), delivery via caesarean section (RR 1.60, 95% CI 1.39–1.84; I2 = 95%) and postpartum haemorrhage (RR 1.98, 95% CI 1.22–3.22; I2 = 84%). Similarly, IP was associated with increased risk of adverse perinatal outcomes including low APGAR score (RR 3.0, 95% CI 1.23–7.35; I2 = 95%), stillbirth (RR 4.75, 95% CI 2.54–8.86; I2 = 9%) and perinatal mortality (RR 4.75, 95% CI 2.67–8.48; I2 = 37%). This meta-analysis suggests that pregnant women with IP may be at increased risk of perinatal complications and adverse neonatal outcomes. However, data remains inconclusive considering the low quality and high heterogeneity of included studies.