Isolated oligohydramnios is not associated with adverse perinatal outcomes.

OBJECTIVE To examine fetal growth and perinatal outcomes in pregnancies with isolated oligohydramnios. DESIGN A cohort study. SETTING Multiple clinics and hospitals. POPULATION Low risk pregnant women. METHODS We used data from the multicentre clinical trial of Routine Antenatal Diagnostic Imaging with UltraSound (RADIUS), in which 15,151 low risk pregnant women were randomly assigned to the ultrasound screening group or the control group. Women in the screening group underwent sonographic exams at 15-22 and 31-35 weeks of gestation. Both groups could have clinically indicated sonographic exams at any time. MAIN OUTCOME MEASURES We used changes of fetal weight z-score to assess whether fetal growth was compromised from the diagnosis of oligohydramnios until delivery, using a repeated-measures regression. We used a combined perinatal index as an indicator of adverse perinatal outcome, which consisted of severe perinatal morbidity and mortality. RESULTS Oligohydramnios (amniotic fluid index < or =5 cm) was diagnosed in 1.5% (113/7617) of women with ultrasound screening compared with 0.8% (57/7534) among the controls. Approximately half of the oligohydramnios cases in the screening group were isolated with no clearly associated factors (e.g. premature rupture of the fetal membranes, congenital anomalies, diabetes, hypertension, postdate and intrauterine growth restriction). Fetal weight centiles in isolated oligohydramnios cases did not change significantly from diagnosis until delivery. Pregnancies with isolated oligohydramnios had perinatal outcomes similar to pregnancies with a normal amniotic fluid index. CONCLUSION Isolated oligohydramnios is not associated with impaired fetal growth or an increased risk of adverse perinatal outcomes.