The etiology of excessive amniotic fluid is complex, some of which can be explained and some of which are still unclear. Fetal malformations are the main cause of excess amniotic fluid, so the choice of whether to do chromosomal testing in patients with unexplained excess amniotic fluid is often a more difficult one for both doctor and patient. If the ultrasound is normal, the risk of chromosomal screening for fetal abnormalities is <1%; however, when the ultrasound suggests two or more abnormalities, further fetal chromosomal testing is required to confirm the presence of fetal abnormalities.