A review of Idiopathic Hydramnios and Pregnancy Outcomes

Idiopathic hydramnios is defined as hydramnios that is not associated with congenital anomalies of the central nervous system or gastrointestinal tract, maternal diabetes, isoimmunizaton, fetal infection (CMV or toxoplasmosis), placental tumors, or multiple gestations. Hydramnios is diagnosed when the AFI is 2 >= 24 or a >= 25 (2 >= 95 or 2 >= 97.5%), the single deepest pocket (SDP) as being >= 8, or the examiner's subjective assessment of having an increased amount of amniotic fluid volume. The prevalence of hydramnios is 1%-2% with 50%-60% of those cases as being idiopathic. A PUBMED search from 1950 to 2007 and Science Citation search from 2001 to 2007 revealed only 3 studies that compared pregnancies with idiopathic hydramnios to pregnancies without hydramnios, and 4 studies that evaluated perinatal mortality with hydramnios after correcting for congenital anomalies. Idiopathic hydramnios was found in the larger studies to be linked to fetal macrosomia, an increase in the risk of adverse pregnancy outcomes, and a 2- to 5-fold increase in the risk of perinatal mortality. Tests that may be helpful in the antenatal evaluation of these at-risk pregnancies are: Doppler flow velocimetry of the middle cerebral artery, nonstress test, biophysical profile, and contraction stress test. Prospective studies are needed in this area that is understudied where risk of an adverse pregnancy outcome and perinatal mortality are increased.