The normal amniotic fluid index also known as amniotic volume index (AVI) is 12-14 cm. The reading of 18 indicates a mild increase. The causes of this are several and include high blood sugar, fetal malformations and infections. The vast majority of patients with a high AVI do not have any specific cause. A careful ultrasound scan can exclude most (but not all) malformations. Blood tests on the mother are useful to exclude specific infections. Elevated blood sugars are a common cause. These can be assessed be simple blood tests. Once these sinister causes have been excluded the fluid needs to be monitored frequently and a premature rupture of the water bag needs to be prevented by restricting the activity of the patient and treating the underlying cause if discovered. By itself this is not a problem to be alarmed about.