High Amniotic Fluid (Polyhydramnios) in Pregnancy: Causes & What to Expect

Question
I'm 33 wks pregnant but measuring 38 (1cm dilated/ 20% effaced), so my doc ordered an ultrasound.  The baby was around 5 1/2 to 6 lbs, and the tech said I have too much fluid.  She said the normal range is 5 to 25.  Last time (27 wks) it was 15.  This time is was 25.6.  She said that any number of things could have caused the jump in fluid and that my doc would probably re-test me for gestational diabetes.  What other things might cause it and/or what questions should I ask my doc when she calls?

Answer
In addition to diabetes, excess amniotic fluid can be caused by problems with the stomach or esophagus of the baby (esophageal atresia). If there is a blockage or difficulty in swalling of the fetus, the fetal kidneys continue to produce amniotic fluid, but the baby does not swallow it and it builds up in the amniotic sac. Too much amniotic fluid can cause maternal dyspnea or premature labor. It can be caused by trisomy 18, anencephaly, and spina bifida, placental abnormalities, multiple gestation, and isoimmunization. In 1% of cases, the cause is unknown.