Occasionally pregnancies are complicated by excess amniotic fluid or polyhydramnios. This can be diagnosed by ultrasound. In most cases the excess fluid does not harm the baby, but as the uterus (womb) is often much larger than it would otherwise be, the woman may be at increased risk of premature labour, which depending on the gestation carries risks to the baby when it is born. In certain circumstances to try and reduce this risk amnioreduction or removal of amniotic fluid can be performed.
Definition from Leeds Teaching Hospitals NHS Trust: amnioreduction [not working]