Polyhydramnios occurs when the volume of amniotic fluid that surrounds the baby is more than normal. Amniotic fluid levels change daily, so repeat ultrasounds are recommended. The incidence rate of polyhydramnios ranges from .1% to 3% of pregnancies.
While polyhydramnios occurs as an isolated condition in 50% of cases, a detailed ultrasound of the fetal anatomy is recommended as the condition can occur as a result of other fetal anomalies and chromosomal abnormalities. Polyhydramnios is associated with agenesis of the corpus callosum, anencephaly, cardiac malformations, cleft lip and cleft palate, congenital diaphragmatic hernia, cystic hygroma, Dandy-Walker malformation, gastroschisis, holoprosencephaly, omphalocele, trisomy 13, trisomy 18, Turner syndrome, and skeletal dysplasias such as osteogenesis imperfecta and thanatophoric dysplasia.
Polyhydramnios is associated with an increased risk of preterm labor, with the frequency ranging from 11% to 29. The perinatal mortality rate for polyhydramnios is 4 per 1,000 births. The recurrence risk depends on the underlying cause of the condition, so a detailed fetal anatomy ultrasound, fetal karyotype testing, and a full family history are recommended.