Introduction
Polyhydramnios is present in approximately 2% of pregnancies and it has been associated with a variety of adverse pregnancy outcomes.

Objectives
The aim of our study was to evaluate the association between polyhydramnios and adverse pregnancy outcomes.

Methods
This was a retrospective case control study of 288 singleton pregnancies delivered in the Rotunda Hospital, Dublin, between 2013 and 2014. Polyhydramnios was defined as: (i) amniotic fluid index (AFI) ≥ 25 cm; (ii) maximal vertical pocket (MVP) of ≥8 cm; and (iii) a gestational age‐specific threshold for AFI. Demographic information, obstetric and neonatal outcomes were obtained by review of hospital databases. Exclusion criteria included gestational or pre‐existing diabetes, multiple pregnancy, carrying a fetus with structural or chromosomal abnormalities, Rhesus factor isoimmunisation, and TORCH screen positive. Outcomes were compared with outcomes of those without polyhydramnios.

Results
A total of 8798 deliveries occurred during the study period. The frequency of polyhydramnios was 1.6%. One hundred and forty‐four women were selected in each group. There was no significant difference in preterm deliveries, low birth weight, low Apgar score at one minute and five minutes and perinatal mortality. However, increase in caesarean delivery rate (43.1% vs 21.5%), number of fetal distresses (17.4% vs 6.9%) and number of neonatal intensive care unit (NICU) admissions (17.4% vs 4.9%) were observed in our study.

Conclusion
In conclusion, idiopathic polyhydramnios is associated with specific adverse outcomes, such as higher rate of caesarean delivery, fetal distress and NICU admissions. Therefore, close surveillance of these pregnancies is required, especially near term.