A comprehensive overview on idiopathic polyhydramnios and associated complications.Review article.Department of Obstetrics and Gynaecology, First Faculty of Medicine, Charles University and Hospital Na Bulovce, Prague, Czech Republic; Department of Obstetrics and Gynaecology, Second Faculty of Medicine, Charles University and Motol University Hospital, Prague, Czech Republic.Literature search using the databases Web of Science, Ovid, Cochrane, Medline databases and an analysis of articles published in peer-reviewed journals with impact factor in the years 1958-2020.Polyhydramnios occurs in 0.2-2% of pregnancies. Pregnancies with polyhydramnios are more often complicated by abnormal foetal lie or presentation and, moreover, should be associated with adverse pregnancy outcomes, particularly with the higher incidence of intrauterine foetal death, placental abruption, labour induction, caesarean sections, prolonged first stage of labor and shoulder dystocia.The moderate and severe forms of idiopathic polyhydramnios are associated with the higher risk of adverse pregnancy outcomes that implies the need for intensive monitoring of a pregnant woman and the foetus both in pregnancy and during the delivery itself.