Uterine artery blood flow response to correction of amniotic fluid volume

OBJECTIVE: Our purpose was to investigate whether acute alterations of amniotic fluid volume affect uteroplacental perfusion. STUDY DESIGN: Three groups of patients of comparable gestational age were studied in a fetal medicine referral unit: (1) eight pregnancies with severe polyhydramnios because of twin-twin transfusion syndrome undergoing therapeutic amnioreduction, (2) seven with severe oligohydramnios undergoing diagnostic amnioinfusion, and (3) six control women having invasive procedures of similar duration without manipulation of amniotic fluid volume. Color Doppler imaging was used to measure uterine artery impedance index values and quantitative blood flow before and within 15 minutes of the end of the procedure. RESULTS: Quantitative flow measurements increased after amnioreduction (74% median increase of volume flow, range 22% to 329%, p< 0.01) and decreased after amnioinfusion (33% median decrease of volume flow, range 17% to 51%, p< 0.05). Impedance index values increased after amnioinfusion (25% median increase in pulsatility index, range 4% to 71%, p< 0.05) and did not alter with amnioreduction. There were no significant changes in the control group. CONCLUSION: Acute changes in amniotic fluid volume after uteroplacental perfusion. In twin-twin transfusion syndrome amelioration in uterine flow may improve fetal condition and explain in part the success of serial amnioreduction therapy.