AQP9 and oligohydramnios: In our previous study (Zhu et al. 2009; Jiang et al. 2012), AQP1 and AQP9 expression in the amnion was decreased in pregnancies with isolated oligohydramnios, so pregnancies with oligohydramnios and a normal AF volume were selected to establish the correlation between AQP1 and AQP9 protein expression.